VIRUS DISEASES

AND OTHER DISORDERS

WITH VIRUSLIKE SYMPTOMS

OF STONE FRUITS IN

NORTH AMERICA

Agriculture Handbook 10

5DEPART:MENT OF AGRICULTURE
VIRUS DISEASES AND OTHER DISORDERS WITH VIRUSLIKE SYMPTOMS

OF STONE FRUITS IN NORTH

AMERICA

x::

C3

UNITED STATES DEPARTMENT OF AGRICULTURE

Agriculture Handbook 10

UNITED STATES GOVERNMENT PRINTING OFFICE

WASHINGTON : 19Î1

For sale by the Superintendent of Documents, U. S. Government Printing Office

Washington 25, D. C. Price $2.50

UNITED STATES DEPARTMENT OF AGRICULTURE

Agriculture Handbook 10

Washington, D. C. Issued April 1951

VIRUS DISEASES AND OTHER DISORDERS WITH VIRUSLIKE SYMPTOMS

OF STONE FRUITS IN NORTH

AMERICA'

Introduction

Virus diseases of peach

Peach yellows

Little peach

Peach rosette

Red suture

Rosette mosaic

Phony

Peach mosaic

^" X-disease

'-Western X-disease

Yellow bud mosaic

Wart

Peach mottle

Muir peach dwarf

Ring spot

Peach necrotic leaf spot . .

Asteroid spot

Golden-net

Peach calico

Peach blotch

Willow twig

Virus diseases of sweet cherry

-^ Buckskin

Albino

Mottle leaf

Rusty mottle

Mild rusty mottle

Necrotic rusty mottle ....

Lambert mottle

Little cherry

Small bitter cherry

Rasp leaf

Twisted leaf

CONTENTS

Page

V

1

1

4

7

11

14

17

16

1>7

43

53

5Ó

59

63

71

81

84

88

90

93

98

98

103

106

112

116

120

123

126

130

132

135

Virus diseases of sweet cherry—Continued

Black canker

Cherry rugose mosaic

Tatter leaf

Pinto leaf

Rough bark of oriental flowering cherry

Virus diseases of sour cherry

Sour cherry yellows

Green ring mottle

Pink fruit

Necrotic ring spot

Virus diseases of plum and prune ....

Prune dwarf

Prune diamond canker

Line pattern

Plum white spot

Standard prune constricting mosaic. .

Ring pox of apricot

Virus diseases of almond

Almond calico

Drake almond bud failure

Viruslike diseases not proved transmissible

Sweet cherry crinkle leaf

Sweet cherry deep suture

Almond bud failure

Noninfectious plum shot hole

Italian Prune leaf spot

Italian Prune sparse leaf

Peach variegation

Deficiency and excess troubles that resemble virus diseases

Similarity of some nutritional disorders and virus diseases

Page

137

139

141

147

149

152

152

159

162

164

171

171

175

177

183

185

187

189

189

191

195

195

201

205

208

210

212

213

215

215

^ Project under the Research and Marketing Act of 1946. By action of the council in

March 1946 the American Phytopathological Society gave special approval to the handbook

as the type of monographic material it favored for publication.

in
Deficiency and excess troubles that resemble virus diseases—Continued

Key to nutrient deficiencies in peacb

trees 220

Nitrogen deficiency 222

Potassium deficiency 224

Phospborus deficiency 228

Iron chlorosis 230

Magnesium deficiency 233

Manganese deficiency 235

Zinc deficiency 237

Copper deficiency 241

Calcium deficiency 243

Boron deficiency 244

Boron-excess injury 246

Page

Deficiency and excess troubles that resemble virus diseases—Continued

Sodium-excess injury 249

Arsenic injury 250

Literature cited 252

Virus and nontransmissible viruslike

diseases 252

Deficiency and excess troubles that

resemble virus diseases 265

Appendix 269

Common and scientific names of

plants 269

List of authors 270

References to virus diseases described

too late for inclusion of sections 272

Host-disease index 273
INTRODUCTION

At the Second Stone Fruit Virus Conference held at Cleveland, Ohio, in 1944

under the chairmanship of V. R. Gardner, a publication committee, consisting

of Rye members, was appointed and requested to revise the text of the Handbook of Virus Diseases of Stone Fruits in North America (96).'^ This committee was asked also to include ( 1 ) illustrations either colored or black and

white for each disease and (2) sections on certain nonvirus and nutritional

disorders, the symptoms of which might be confused with those associated with

virus diseases.

Stone fruits are necessarily grown in sections affording suitable cultural

factors and markets. These sections, especially in western North America, are

widely separated geographically. Virus diseases affecting stone fruits occur in

all the sections, but they are most prevalent in those where a large number of

different kinds of these fruits are associated.

Since some of the diseases are known to have rapid rates of orchard spread,

a general policy of carrying on investigations only in the districts of occurrence

has been generally followed. The sporadic and wide distribution of the diseases has led to work by a relatively large number of investigators in widely

dissociated districts. To bring the results of these studies together, the

publication committee adopted the policy of requesting the active cooperation

of all investigators known to be working on virus diseases of stone fruits.

The plan was to include sections for only diseases which had previously been

described in the literature. For each disease a subcommittee consisting of

investigators who have been or are actively engaged in research on it was set

up. The chairman of each subcommittee, chosen on the basis of original or

comprehensive reports, was asked to act as senior author for the section on

the disease in question. Except as indicated, associate authors are listed alphabetically without attempt to evaluate the amount of work to their credit.

Previously unreported data on some of the diseases are included. In some

instances individual responsibility and credit for such data are given by footnotes or directly credited statements in the text. Otherwise each group of

authors is responsible for the statements of fact and opinion.

Up to 193 0, only 5 virus diseases had been reported on stone fruits and all

of these affected peach. Since then, in the short period of approximately 20

years, over 40 new ones have been reported—variously aflfecting peach,

nectarine, plum, sweet cherry, sour cherry, apricot, almond, and many ornamental and wild species of Prunus, The discovery of new diseases has been

so rapid that factual information concerning many of them is incomplete.

Information is particularly short on host range, symptomatology, economic

importance, vectors, relative rate of orchard spread, the presence and relationship of virus forms and strains, and other factors important to control.

It is the purpose of this handbook to bring together up-to-date information

and to aid recognition of the diseases by including illustrations of diagnostic

symptoms. It is beUeved that the handbook will be useful to students,

growers, nurserymen, regulatory officials, and others, and will assist investigators, especially those widely separated geographically, in comparing results

and in planning coordinated research. It is hoped that revisions will be made

as new information becomes available.

Since virus diseases are still regarded by some as having a certain amount of

mystery, it seems necessary to include some general statements about the nature

of their causative agents. Viruses are becoming more commonly considered by

^Italic numbers in parentheses refer to Literature Cited, p. 252.
authorities to be very small efficient parasites, which can live and multiply only

in the tissues of their plant or animal hosts. They vary in shape and size: the

largest approximate the size of small bacteria and the smallest are generally

larger than any of the chemical molecules of their hosts. Some of the common

diseases of man caused by viruses are smallpox, mumps, influenza, and measles,

and among those of animals are hog cholera, rabies, and foot and mouth disease

of cattle.

In plants, viruses cause diseases characterized by a variety of symptoms.

Diseases named "mosaic" from their most prominent symptom are common

on many vegetables and weeds and even on shrubs and trees. Other symptoms

of virus infection are yellows, leaf curls, excrescences, rosettes, stunts, tissue

killing, and even killing of the entire host plant.

In nature, plant viruses are commonly spread by insects, most commonly by

those with sucking mouth parts such as aphids, leafhoppers, mealy bugs, and

white flies. These insects feed upon plants infected by a virus and take some

of the juice containing the virus with them when they migrate to healthy

plants, into which they introduce the virus in the process of feeding. Only a

few of the vectors are known for virus diseases of stone fruits. Some viruses

pass from one host generation to the next through seeds. The only experimental method by which viruses have been transmitted mechanically among

fruit trees is some form of grafting.

The incubation period of individual stone-fruit virus diseases varies considerably, depending upon the material and technique. When budding or

some other form of grafting is effected in the fall, symptoms do not usually

appear before the following growing season. In the case of certain virus

diseases, if seedlings or variety trees just breaking dormancy are inoculated

with infected tissue, symptoms may appear within a few days. A few virus

diseases of stone fruits have long incubation periods of more than a year.

Many stone-fruit viruses cause acute, or shock, symptoms and then the host

partially recovers and continues to produce only chronic symptoms. For

others, symptom production is progressive, and there is neither an acute nor

an equilibrium stage.

Since viruses which cause plant diseases are too minute to be seen through

an ordinary microscope and cannot be cultured away from living protoplasm,

their presence can be recognized only by the characteristic symptoms they

produce on their hosts. Thus, the identification of new diseases on the basis

of symptoms only, especially if on a single host, may lead to false interpretations. For instance, different viruses may produce similar symptoms on a

single host or a single virus may produce dissimilar symptoms on different

hosts. Furthermore, a single host may be infected simultaneously by more

than one virus, and the symptoms expressed may be the result of the combined

effect of all or of the effect of only one, the others being latent. Such combinations are difficult to dissociate. The methods for determining such associations consist principally in the establishment of the existence of components

through the use of differential hosts, differential effects of chemical and

physical agents, and dissimilar effects with inoculum from a large number

of sources.

In some virus diseases there is the complication of the existence of forms

or strains of the causal virus capable of producing widely varying symptom

expressions. In such cases and until better methods are developed, there is

bound to be difficulty in establishing identity and mistakes will be made. It

is likely that some of the diseases described in this handbook under separate

names will be found to be caused by the same virus or by strains or forms

of the same virus. Until exact information is available, most workers follow

VI
the practice of describing diseases on new hosts or in new locaHties as new

diseases.

Various systems of naming the causal viruses have been proposed. In most

sections of the handbook names according to Johnson's classification {120)

and those proposed by Smith (211), Holmes {104^ 105), and McKinney

(145) are listed. In some sections names according to the Fawcett (71)

system are also given.

Control is a complex and difficult problem. From a consideration of the

large number of diseases described in the handbook, some of which threaten

the continued culture of stone fruits in some districts, control may present a

dark picture or even appear impossible to some individuals. Without minimizing the difficulties encountered, readers can get encouragement by reflecting

on the outlook of peach growers during the height of the peach yellows

epidemics, when peach growing in some areas seemed doomed. Today, through

unity of effort, peach yellows is no longer considered a major threat to peach

growing.

In general, control can be divided into two phases: (1) Prevention by

exclusion and (2) reduction by diseased-tree removal or application of methods

which reduce the detrimental effects. Individual diseases, often even within

limited localities, present their own problems. Before satisfactory control

measures can be recommended, the nature of the disease, its distribution, host

range, rate and manner of spread, effect on yield, and other facts should be

known.

In the past the general recommendation has been to remove virus-affected

trees from orchards. For certain diseases and in certain districts this procedure

may still be generally recommended. For other diseases there is need for correlated nursery-clean-up and wild-host-removal programs. For certain diseases

already generally distributed and for those which have symptomless hosts,

which spread rapidly, or which have other characters which make diseased-tree

removal impractical, it is necessary to develop other means of control.

Use of resistant or tolerant varieties (varieties which, although infected, are

not materially damaged), use of tolerant or resistant rootstock combinations,

use of mild-symptom-producing virus forms to protect against infection by

more damaging ones, chemotherapy of infected trees, and vector control are

approaches which offer promise as control measures. Heat has been used to

kill certain viruses in infected budwood and nursery trees, and certain chemicals

have reduced infection by others in experimentally inoculated trees. Application of sprays or treatment with chemicals, fertilizers, or other materials has

not resulted in the cure of virus-diseased fruit trees in the orchard.

In view of the evidence that certain virus diseases have been and are still

being distributed in nursery stock, no control procedure is adequate without

provisions to stop such spread. Nurserymen need the assistance of research,

regulatory, and extension men and growers in obtaining virus-free scion wood

and rootstocks and for establishing procedures to keep the growing nursery

stock virus-free. Nursery-improvement programs are under way in various

States but vary in procedure and specifications. There is need for rechecking

and uniformity in some features to cover provisions for interstate shipment.

Plantsmen should be cognizant of abnormalities which are not caused by

infectious agents. For that reason sections describing certain nutritional

deficiencies and excesses and other nontransmissible disorders are included.

Certain of these are easily remedied by application of the deficient elements.

Certain of the bud-perpetuating genetic disorders can be avoided by selecting

bud^vood from unafiected clones.

VII
The report given here is the result of cooperative efforts of the authors of

the respective sections and of others, and it could not have been made except

for their willingness to pool their information and work together. The report

would be incomplete if it were not pointed out that through this cooperative

effort workers have been brought in closer contact, and more opportunity for

comparison of methods of procedure and results and for exchange of ideas has

resulted. It is believed that such association will add much to the solution of

the problems presented by virus diseases.

Special credit is due V. R. Gardner, who, as director of the Michigan Agricultural Experiment Station, called the initial conference in 1941 and who

acted as chairman of subsequent meetings, to J. R. Magness and G. M. Darrow

for suggestions for the manuscript and for assistance in formulating the pubhcation arrangements, and to Annie R. Gravatt and her assistants Lorena

Shannon and Eugene Wooden and other members of the Plant Industry Station

staff for preparing the handbook for publication.

Credit is also due various plant pathologists who contributed ideas and previously unpublished information and to the following who contributed

illustrations for sections of which they are not authors: Harry Andison plate

17, D; L. P. Batjer plate 27, F; Damon Boynton plate 25, C, D; S. R. Cannings

plates 17, B, C, and 18, A; Donald Cation plates 1, C, D, 2, B to D, 24, B, and

25, B, and figures 1 and 2; L. C. Cochran plates 23, A, C, and figure 3;

E. S. Degman plate 16, A; S. B. Fenne plate 1, A, B; W. R. Fisher plate 6, A, JB,

and figure 15; H. L. Garrard plates 23, B, D, and 24, A; A. Leon Havis plate

24, C; Omund Lilleland plate 26, C; Roy C. McCue plates 9, top, 19, and 22;

W. J. Mead plate 1, E, F; H. J. O'Reilly plates 10, B, and 11, D; E. L. Reeves

plate 27, E; A. O. Simonds plate 8, B; Gilbert L. Stout figure 17; Bryce N.

Wadley plate 10, D; F. B. Wann figures 75 and 76; and J. H. Weinberger

plates 2, A, and 23 A, C.

The cuts for plates 9, 19, and 22 were furnished by the Washington State

Department of Agriculture.

The introduction was prepared by the pubhcation committee, composed

of Donald Cation, chairman, G. H. Berkeley, L. C. Cochran, F. P. CuUinan,

and R. J. Haskell. Reference to the handbook should be made directly to

particular authors and sections: for example, Kunkel, L. O., Blake, M. A., and

Manns, T. F. Peach Yellows. In Virus Diseases and Other Disorders With

VirusHke Symptoms of Stone Fruits in North America. U. S. Dept. Agr.

Agr. Handb. 10, pp. 1-3, illus. 1951.

VIII
VIRUS DISEASES OF PEACH

PEACH YELLOWS

By L. O. KuNKEL, M. A. BI.AKE, and T. F. MANNS

Other Common Names of the Disease

None.

Names of the Causal Virus

Peach virus 1, Johnson's classification; Prunus virus 1 (Kunkel) Smith;

and Chlorogemis persicae Holmes.

Geographic Distribution

The disease has been observed from Massachusetts to Virginia on the Atlantic

Coastal Plain and southward along the Appalachian Mountains into the Carolinas; westward to Ontario, Canada, and Michigan; and southward to Indiana,

Kentucky, and Tennessee. Sporadic outbreaks have been reported in New

Hampshire, Iowa, Missouri, Arkansas, Kansas, Texas, and Nebraska, but the

disease has never been established west of the Mississippi or in the South.

History and Economic Importance

This first-known peach virus disease {174, 206, 207, 210) has resulted in

sporadic heavy losses, wiping out entire orchards and even all those in entire

peach districts. Great outbreaks occurred in 1791, 1806-7, 1817-21, 1845-58,

1874-78, 18 86-8 8, and 1920. These periods were followed by periods of relative quiescence. The disease has been of minor importance in recent years

(77, 152). Over most of its range it is now less prevalent than little peach.

Host Range

The following species and varieties are known to be infected: Peach (Prumis

pérsica), all varieties; nectarine (P. pérsica var. nectarina); apricot (P.

armeniaca) ; almond (P. amygdahis) ; Japanese plum (P. salicina) varieties

Abundance, Chabot, and Satsuma; domestica plum (P. domestica) ; myrobalan

plum (P. cerasifera) ; Othello and other ornamental plums (P. cerasifera var.

atropurpúrea) ; and native American plums (P. horttdana and P. americana).

No species of the genus Pruntcs is known to be immune. On myrobalan and

Othello plums the symptoms are masked even though the virus is systemic.

Symptoms

Peach.—Fruits on affected peach trees ripen prematurely (pi. 1, JB), a few

days to 3 weeks or more in advance of normal (pi. 1, A), and are of inferior

quality, usually with a bitter taste ( H ). In varieties that normally develop

red coloring in the skin and around the pit the skin is abnormally highly colored, spotted with red and purple, as shown in plate 1, B, and the flesh is

streaked or marbled crimson with a pronounced red coloring around the pit.

The leaves become chlorotic and yellow, fold upward, and tend to roll and

droop downward. On typically affected trees thin, wiry, willowy shoots

bearing small, narrow, yellow leaves, such as shown in plate 1, C, and figure 1,

are produced and tend to grow upright from the main limbs. Leaf buds

unfold prematurely. In young trees many of the latent buds fail to remain

dormant. These unfold into yellowish leaves, scarcely an inch in length, giv-
2 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

ing the tree a bushy appearance. In advanced cases the ends of the old limbs

die and twigs bearing small yellow leaves are produced from limbs and trunks.

Affected trees normally die in 2 to 6 years, but those affected with mild strains

of yellows may live for a much longer period, particularly if given good cultural treatment.

On greenhouse trees the earliest symptom is the clearing of the veins of the

tip leaves (130). Young leaves at the tips of infected branches stand straight

if healthy and bend over, or are sickle-shaped, if diseased. Production of thin,

upright-growing shoots bearing small, slightly chlorotic leaves is a conspicuous

Figure 1,—Peach tree affected with peach yellow^s (advanced stage), showing clusters

of wiry shoots growing from main arms.
VIRUS DISEASES OF STONE FRUITS Ö

symptom of yellows after the disease is well established. Young trees frequently live 1 or 2 years after infection.

Apricot and other hosts,— On apricot, almond, American and hortulan

plums, David peach (P. davidiana) ^ almond cherry (P. glandtdosa), and

Manchu cherry (P. tomentosa) symptoms are similar to those on peach and

about as severe. On Abundance plum, German Prune (P. domestica), wildgoose plum (P. munsoniana), and Japanese apricot (P. mume) symptoms are

similar to but milder than those on peach. On myrobalan and Othello plums

symptoms are very mild or lacking. On Wickson plum, a hybrid resembhng

P. simonii, symptoms are similar to but more severe than those on peach.

Diagnostic or Unusual Characteristics

Production of slender, upright-growing shoots by affected trees makes peach

yellows easy to diagnose. The disease does not persist in warm peach-growing

districts of the South, probably because of inactivation of the virus by

heat (132).

Transmission

Transmission by budding and grafting has been demonstrated repeatedly

(147). Kunkel (129) demonstrated that the plum leafhopper (Macropsis trimactdata (Fitch) ) transmits yellows; this was confirmed by Hartzeil (79, ^0),

Manns (149), Manns and Davies (151), and Manns and Manns (152),

Kunkel listed negative results for 14 species of sucking insects. Hartzeil

failed to get transmission with 47 species of insects and mites, using 20 species

in significant numbers. Manns listed negative results with several species. A

relatively small percentage of positive transmissions were obtained by the 3

investigators.

Incubation Period

Under orchard conditions the incubation period may be as long as 3 years.

Under appropriate greenhouse conditions it may be as short as 40 days. Peach

yellows virus travels much more rapidly downward than upward; hence, infections produced near the tip of a tree cause symptoms much earlier than

infections occurring at or near the ground level (128). Kunkel (133) showed

that a bud-contact period of 8 to 11 days is necessary for virus transmission.

Control Measures

Care in using only healthy material for propagation and eradication of

diseased trees in orchards as soon as symptoms appear have proved effective

control measures. On the basis of findings by Manns and Manns (153) that

certain infected plum trees Hved for many years and harbored large numbers

of the plum leafhopper, it is suggested that plums not be planted in the

vicinity of peach orchards. Spraying for control of the plum leafhopper is

also suggested.

Remarks

Peach yellows under the present methods of control does not seem to be a

serious disease in well-kept commercial orchards except in isolated instances.
LITTLE PEACH

By T. F. MANNS, M. A. BLAKE, and L. O. KUNKEL

Other Common Names of the Disease

Peach littles.

Names of the Causal Virus

Chlorogemis persicae var. micropersica Holmes; little peach virus; peach

virus 3, Johnson's classification; Prunus virus lA Smith; and little peach strain

of peach yellows virus.

Geographic Distribution

Little peach occurs in eastern United States as far south as North Carolina

and in Ontario, Canada {43, 44), It is found in approximately the same area

as peach yellows.

Economic Importance

Little peach has superseded peach yellows in importance in most districts

in recent years, but in some districts yellows is as potent as ever. It is the most

destructive virus disease of peach in the northern peach-growing districts east

of the Mississippi except in Connecticut, Massachusetts, and New York, where

X-disease is now present.

Host Range and Varietal Susceptibility

The host range of little peach (5, 43, 148, 150, 153) is similar to that of

yellows. Peach {Fntnus pérsica), plums, and apricot (P. armeniaca) are

affected. Manns {150) showed that certain varieties of Japanese plum (P.

salicina), Abundance, Chalco, and Chabot, are symptomless carriers; other

varieties, such as Satsuma and Santa Rosa, and crosses such as Simon may

show symptoms, but live for many years. Myrobalan plum (P. cerasifera),

which is used extensively as a rootstock, is a symptomless carrier. All the

domestica plums and prunes (P. domestica), as well as the wildgoose plum

(P. imtnsoniana) i are susceptible.

Symptoms

On young seedling peach trees the first symptom is a distortion of the young

leaves at the tips of afi^ected branches. Production of an abnormally large

number of short branches along the main stem, especially near the soil level, is

common. These branches are more upright than normal, but not as vertical

as those affected with yellows. Shortening of internodes and general stunting

of the tree result. Newly infected trees are generally of a deeper green color

than is normal for healthy trees. After the disease becomes chronic, the

mature leaves turn slightly yellow and twiggy growth develops along the

branches (pi. 1, D). After 2 or 3 years a smaller number of new shoots are

produced.

On older peach trees the symptoms are at first most prominent on a single

branch or portion of a tree. The foliage is frequently of a darker green color

and appears more compact and bushy than normal. The compact appearance is

due partly to shortened internodes and partly to the increased production of

leaves on short, lateral branches or spurs on the 2- and 3-year-old wood. The

crowded leaves tend to droop, become leathery, bend inward, and curl toward

the branches on which they originate, giving a compact, bushy, and drooping
VIRUS DISEASES OF STONE FRUITS

appearance (fig. 2). An unusual number of short, spurlike shoots frequently

sprout from the bases of the larger limbs. As the disease becomes chronic, the

leaves turn lighter green to yellow. As the disease weakens the trees, the

compact, bushy character of the growth becomes less evident. The fruits on

affected trees or branches (pis. 1, E, and 2, C) are smaller and ripen several

days to 3 weeks later than normal (pis. 1, F, and 2, B). They generally have

an insipid flavor. The pits are reduced in size, and the kernels are either

undeveloped or fail to germinate.

On susceptible plum and apricot varieties the symptoms are similar to those

on peach, but usually much milder.

Diagnostic or Unusual Characteristics

The foliage of diseased trees in the earlier stages is darker than that of healthy

ones and has a heavy leathery appearance. Blake (10) did not regard a darker

green in early stages of little peach as of diagnostic value. The fruits usually

mature several days or more later than is normal and are smaller. Manns has

observed that where Japanese beetles (Popillia japónica Newm.) are abundant

trees affected with peach yellows and little peach are infested by thousands of

the insects, whereas the healthy trees attract few.

Figure 2.—Peach shoot showing drooping, clustered foliage, a symptom characteristic

of little peach, in contrast -with unaffected shoot at right.
6 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Transmission

Transmission is effected by budding or grafting of the root or top with

infected tissue and by means of the plum leafhopper {134, 148, 150, 153).

Incubation Period

The incubation period (13 3, 150) in the field may vary from 1 to 2 years

after budding with infected tissue, but in the greenhouse it may be less than

2 months under optimum conditions.

Thermal Relationships

The little peach virus is inactivated by heat treatment at the same temperature and exposure that proved effective for the control of peach yellows {131),

Immunologie Relationships

Kunkel {13 0, 131) showed that peach trees having little peach virus are

immune from infection by peach yellows virus and that likewise trees having

yellows virus are immune from infection by little peach virus, but that neither

of the causal viruses of these diseases gave any protection against peach

rosette virus. Manns {150) reported that when healthy bearing trees are

budded simultaneously near the growing points with one bud infected with

peach yellows virus and another with little peach virus, the yellows symptoms

will be the first to show, but that very shortly afterward the little peach

symptoms will appear and be the dominating ones. However, Kunkel {13 3)

showed that, when peach seedlings are simultaneously inoculated with peach

yellows and little peach viruses by budding, the bud placed in the top position

determines the nature of the acquired disease.

Blake questioned whether it is correct to say that trees having little peach

virus are imm^tne from yellows, he and associates having occasionally found

trees which had one branch with a distinct case of yellows and another with a

distinct case of little peach {11). On one branch the fruits prematured, while

on another they were immature.

Control Measures

Diseased trees should be removed as soon as discovered. Removal or indexing

of suspected masked carriers (plums and certain other species of Prnmts) and

the use of contact sprays to eliminate the insect vector {Macropsis trimaculata (Fitch)) are suggested {150).

Remarks

Little peach is spread by the same vector, is inactivated by similar heat

treatment, and has a similar host range and approximately the same geographical distribution as peach yellows {134, 148, 150, 153). Little peach virus

also protects a plant against infection by peach yellows virus. For these

reasons, the little peach and peach yellows viruses are considered to be closely

related and strains of the same virus.
PEACH ROSETTE

By J. A. MCCLINTOCK, L. O. KUNKEL, and H. H. THORNBERRY

Other Common Names of the Disease

None.

Names of the Causal Virus

Peach rosette vims; peach virus 2, Johnson's classification; Prunus virus 2

(McCHntock) Smith; Namis rosettae Holmes; and Carpophthora rosettae

Holmes.

History and Geographic Distribution

Peach rosette was first noted in Georgia about 1881 {207, 208), Subsequently the disease was reported in Alabama, South CaroHna, Tennessee, West

Virginia, Missouri, and Oklahoma (143). It has been reported also in Kentucky, Illinois, Indiana, Arkansas, and Kansas.

Economic Importance

Peach rosette has caused serious losses locally in peach orchards, but it is of

minor importance in comparison with peach yellows, little peach, phony, and

peach mosaic. It could become of greater importance if established in native

stands of Pnmus pttmila bordering peach orchards in the Great Lakes area.

Host Range and Varietal Susceptibility

Peach rosette virus causes symptoms on peach (P. pérsica) ; apricot (P.

armeniaca) varieties Moorpark, Royal, and Wilson; almond (P. mnygdahis)^

mazzard cherry (P. avmm)\ sour cherry (P. cerastts) seedlings; chickasaw

plum (P. angustifoUa) \ Japanese plum (P. salicina) varieties and hybrids

Kelsey, Ogon (Botan), Maynard, and Red June; damson plum (P. insititia);

and sand cherry (P. ptimila). Natural infections have been recorded on peach

and chickasaw plum in southern United States.

Thornberry {237) reported that Wilson apricot approaches the category of

a symptomless carrier. Marianna plum, a hybrid variety used principally as a

stock, was shown by McClintock {143) to be immune from infection by the

peach rosette virus.

Tobacco {Nicotiana glutinosa), periwinkle (Vinca rosea), and tomato

{Lycopersicon esculentum) were infected by transmission of peach rosette

virus from affected peach trees through dodder {Ctiscuta campestris

Yuncker) {13 5).

Symptoms

Peach,—Peach-rosette-aifected trees {ûg, 3) are more striking in appearance than trees affected with peach yellows. The disease is more rapid in

progress than peach yellows. Symptoms generally appear with the recurrence

of growth in the spring. The first-formed leaves are normal in size for the

variety, but commonly they fold inward or arch backward. The leaves usually

turn yellow in contrast with the various shades of green in healthy leaves.

On these first-formed leaves red spots develop, and usually the leaves fall in

early summer. As new terminal growth has extremely short internodes, the

newly formed leaves are closely appressed into distinct rosettes (pi. 2, A),

The older of these leaves are progressively shed, leaving only tufts of younger

leaves near the tips of naked twigs.
HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

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figure 3,—Elberta peach tree affected with peach rosette, showing contrast with

a normal branch at far left.

Trees of bearing age usually produce blossoms, but they do not set and

mature fruits on branches which show leaf symptoms. In the majority of

cases peach-rosette-affected peach trees die within the year in which symptoms

first appear, but exceptions to this were observed by McClintock (143) in

peaches growing on peach-rosette-immune Marianna plum stock.

Plum.—On chickasaw plum rosette symptoms are much less striking than

on peach. Shortening of the internodes is less pronounced, and usually there

is less premature defoliation of infected plums. On this species of plum the

virus appears to be less virulent; therefore infected wild plums may survive

for more than a year after symptoms become identifiable. From these observations McClintock concluded that the wild chickasaw plum and related southern

species or hybrids are the native hosts of peach rosette virus. Infected wild

plums in proximity to orchards are suspected of being the major source of

inoculum for cultivated stone fruits. On damson plum symptoms consist of

resetted growth and mottled leaves. Affected Maynard plum trees are stunted,

and the growth is resetted.

Apricot.—On affected Royal apricot the shoots are weak and have shortened

internodes, but they are not resetted as severely as affected peach. The growth

is stunted, and the leaves are mottled. On Moorpark apricot the growth is

stunted, and the leaves are mottled greenish yellow (143). On Wilson apricot

the symptoms are extremely mild. There is a tendency for witches'-brooms

to form and for the number of shoots from main branches to increase. The

leaves are not mottled but are slightly yellowed, and the petioles turn reddish.

The trees may show some stunting of growth, especially when they are infected when small. Otherwise, Wilson apricot approaches the category of a

symptomless carrier (237).

Other hosts.—On affected almond the growth is stunted and the leaves

are yellowish green and resetted.
VIRUS DISEASES OF STONE FRUITS 9

On mazzard cherry afiected with peach rosette the growth is markedly

reduced, and the leaves are smaller and more rolled than normal ones during

the second season. The leaves are yellowish green, and the growth is tufted

as on affected peach. The terminal buds fail to become dormant. Resistance

was indicated in mazzard, as one affected tree remained alive for 23 months

after the appearance of the symptoms.

Symptoms resembling those of peach rosette were seen on seedlings of sour

cherry growing near infected peach {23 6).

On affected sand cherry there was a witches'-broom growth of the new

shoots and the leaves were smaller and lighter green than those of healthy

plants, but affected plants were not killed.

On periwinkle peach rosette virus causes rosettes similar to those on peach.

It causes wilting and death of rapidly growing tomato and tobacco.

Diagnostic or Unusual Characteristics

The quick death of infected peach trees makes peach rosette on this host

partially self-eradicating (243). Evidence to date indicates that apricots and

wild and cultivated plums are more resistant to the lethal effects than are

peaches. Although peach rosette is of southern habitat, the symptoms produced on peach by artificial inoculation in Michigan were characteristic of

those reported in the South.^ These findings, coupled with the northward

progress of natural infections, indicate that this disease could become of

importance in northern orchards.

Transmission

Natural spread from infected wild plums to cultivated plums and peach and

from diseased to healthy trees in orchards is apparent, but no vector is known.

Attempted transmissions with sap and insects were negative (144). Budding

or grafting of tops or roots of peach and plums transmits the virus provided

tissue union results between diseased and healthy plants (209). The virus

was apparently transmitted through dodder from peach trees to periwinkle,

tomato, and tobacco. Serial transmission in these species has been effected by

grafting. The virus has not been transmitted from herbaceous hosts to peach

by grafting or through dodder.

Incubation Period

The first appearance of symptoms varies under field conditions, depending

on the season of the year and the point of inoculation. Kunkel (13 3) determined that a bud-contact period of 8 to 14 days is necessary for virus

transmission from peach to peach.

Thermal Relationships

Kunkel (131) found peach rosette somewhat more refractory to heat treatment than little peach, red suture, and peach yellows. Peach rosette virus in

bud sticks was destroyed by 8- and 10-minute treatments at 50° C. It was

not destroyed in buds exposed as long as 2 hours at 40°.

Control Measures

Systematic eradication of infected trees in orchards and of native wild

Pntnus growing near orchards as soon as symptoms are observed has proved

effective and is recommended. If diseased trees are allowed to remain in the

orchard, peach rosette has been observed to increase rapidly and reach epidemic

proportions, affecting whole orchards in 3 to 5 years. Even under these con-

^ Cation, D. Correspondence with tKe authors.

891793°—n—2
10 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

ditions spread can be reduced to a few trees within 1 or 2 years by prompt

diseased-tree removal in the spring.

Remarks

Kunkel (13 0) showed that peach yellows and Httle peach produce no

inhibiting eflfect in peach against infection with peach rosette virus. Determination of the natural host range and the vectors would contribute to the

control measures that could be recommended.
RED SUTURE

By DONALD CATION and C. W. BENNETT

Other Common Names of the Disease

None.

Names of the Causal Virus

Red suture virus; Prunus virus 4 (Bennett) Smith; peach virus 5, Johnson's

classification; and Chlorogemis persicae var. vtdgaris Holmes.

History and Geographic Distribution

Red suture occurs in Michigan and Maryland (5, 244). Trees inoculated

with the virus from Maryland and Michigan showed that the virus from both

sources produced the same disease. A few suspected cases were reported from

southern Indiana. There is evidence that red suture was present in Michigan

as early as 1911 (23 0), but thus far it has not been reported with certainty

from any other peach-growing section except Maryland, where it probably was

introduced on infected nursery stock.

Economic Importance

Red suture on peach is responsible for annual losses of up to 3 percent of the

trees in districts where it is established, and periodic losses in epidemic years

involve large portions of entire orchards. On the whole, red suture is of less

importance than little peach in Michigan.

Host Range and Varietal Susceptibility

Red suture is known to occur only on peach {?runus pérsica) and Abundance variety of Japanese plum (P. salicina). Results of graft-inoculation

tests made by Cation indicate that sweet and sour cherries (P. avmm and P.

cerasus) are immune. No immune varieties of peach have been found.

Symptoms

Peach.—Symptoms of red suture are found on both the fruits and the

foliage (5, 44). Infection also produces a characteristic type of tree growth.

The fruits ripen several days prematurely, particularly on the suture side,

which softens and may be fully mature while the other side is still green and

hard. The suture side is frequently, but not always, swollen or bulged (pL

2, E). On the side that ripens early, the flesh is rather coarse, stringy, and

exceptionally watery. Many of the fruits have a rough, bumpy contour, more

pronounced on the suture side. The early-ripening side of red-colored fruits

is splashed or blotched with an abnormally dark red to purple, the color being

more pronounced on the apexes of the bumps. Yellow-colored fruits, such as

those of Gold Drop, are not reddened but are deeper yellow on the suture side.

The flavor of the fruits is usually, but not always, insipid. The suture side

tends to bruise or break down in shipment, resulting in a loss in marketing.

Trees with red suture are generally off-color as compared with adjacent

normal trees. A diseased tree as a whole presents a yellowish-green to greenishbronze appearance, but if heavily fertilized with nitrogen it may have a green

color approaching normal. The difference in color of diseased and healthy

trees is more noticeable at certain periods in the season, particularly several

weeks after petal fall and also just prior to fruit maturity. Diseased trees

11
12 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

usually take on autumnal coloration prematurely. In diseased trees many

vigorous 2-year-old branches show a characteristic type of growth. On such

branches buds develop and grow into short spurlike outgrowths with a resulting crowding and clustering of the leaves along the branch (pi. 2, D). On

similar branches of a normal tree some of the buds remain dormant, a few

grow long shoots, and only a few develop into spurlike growths. A tree that

has had the disease for several years shows less dense interior growth than

normal. Diseased trees may live for 8 years or more.

Phí77i.—On the variety Abundance, Cation found that symptoms are

indistinguishable from those caused by peach yellows. Affected trees have a

lighter color than normal, and the fruits ripen a little early. The varieties Red

June (P. salicifia) and Wickson (P. salicina X ^^ shnonii) show severe

symptoms when affected with peach yellows, but these varieties were little

affected with the red suture virus.

Diagnostic or Unusual Characteristics

Peach trees with red suture are very similar to those with little peach in

type of tree growth and in foliage characteristics. Red suture is diagnosed

most readily from fruit symptoms and is distinguished from little peach by a

preponderance of bulged sutures and early, uneven ripening of the fruit.

Diseased trees are most easily detected in orchards receiving good culture.

Peach trees inoculated with both red suture and rosette mosaic viruses or

with red suture and sour cherry yellows viruses will show rosette mosaic or

sour cherry yellows, respectively, the following season, according to Cation.

Peach trees grafted concurrently with buds infected with red suture and peach

yellows viruses will show the symptoms of the disease represented by the uppermost bud.

Transmission

Transmission has been accomplished by grafting with bark tissue, with or

without buds, from diseased trees. Graft inoculations with leaf or fruit tissue

have not been attempted. The results of inoculations by means of the plum

leafhopper (Macropsis trimacidata (Fitch) ) have been negative, but there were

too few of them to be conclusive.

Incubation Period

In the field the symptoms on a mature tree appear the second year, or 22

months after inoculation. Symptoms are not apparent on 1-year-old nursery

trees grown from diseased buds and frequently not in the second year of

growth.

Thermal Relationships

Kunkel (131) found that the red suture virus is inactivated by heat, particularly when bud sticks are immersed in a water bath at 50^ C. for 3

minutes. The thermal-inactivation point is very close to that of the peach

yellows and little peach viruses.

Control Measures

In most places red suture has been kept in check by periodic orchard inspection and removal of diseased trees, but in a few localities it is endemic. The

nursery practice of indiscriminate purchase of propagating material from

growers should be discouraged. Indirect evidence indicates that such practice

was responsible for the spread of the disease from Michigan to Maryland.

Preferably bud sticks should be taken from inspected trees or from those in

orchards containing no disease. Heat treatments could be used to insure
VIRUS DISEASES OF STONE FRUITS 13

freedom from disease if the propagation wood is questionable. Nursery inspection is of little value, since symptoms are not evident on young trees.

Remarks

On the basis of disease symptoms and the thermal-inactivation point of the

causal virus (131), red suture appears to be related to peach yellows and

little peach. It seems probable that the red suture virus may have arisen

from the peach yellows or the little peach virus by mutation. The restricted

distribution of red suture indicates that, if the virus is a mutant in the peach

yellows group, such mutants occur rarely.
ROSETTE MOSAIC

By DONALD CATION

Name of the Disease

The disease was first described on peach and was called "rosette mosaic/'

a name which refers to two of the outstanding symptoms.

Name of the Causal Virus

No Latin binomial has been proposed, and for convenience the virus will be

referred to as rosette mosaic virus.

History and Geographic Distribution

The disease has been present in Berrien County, Mich., at least since 1917

(45, 50) and has been found subsequently in a few scattered orchards in that

county. A few cases have also been reported in New York (S2),

Economic Importance

Rosette mosaic seriously affects production of individual trees, but because

of the relatively few infected trees in Michigan it has not been of great importance. The disease is locally serious in Eau Claire Township, Berrien

County, Mich., where there was a considerable increase in incidence in 1947.

Host Range and Varietal Susceptibility

So far as known the virus of rosette mosaic is limited to peach {Frunus

pérsica) and plums. All varieties and seedlings of peach tested proved

susceptible, the severity of reaction varying with the variety. The following

varieties of peach are listed in the order of the severity of effect of the disease:

South Haven, Halehaven, J. H. Hale, Elberta, Carman, Golden Jubilee, Kalhaven, Ambergem, and Gold Drop. Damson plum (P. insititia) and Burbank,

Red June, and Abundance plums (P. salicina) appear to be symptomless carriers, but Italian Prune (P. domestica) and Wickson (P. salicina X ?*• simonii)

plums express symptoms.

Symptoms

Peach.—-The symptoms on peach may consist of delayed foliation; chlorotic

mottling of early-formed leaves, generally accompanied by distortion (ñg.

4, A); and a shortening of internodes, which frequently crowds the leaves into

a so-called rosette. These symptoms are somewhat variable because there are

forms of the virus, and the peach varieties respond differentially.

When chlorosis of the leaves occurs, it is evident early in the season.

Chlorotic areas vary in size and shape and range from yellow or cream color

to translucent. Tissue growth in these chlorotic areas is retarded, and distortion results. Less definite retardation gives a wavy, or undulating, leaf

margin.

Leaves formed later in the season on afiiected trees appear more normal in

size and shape, but actually they are about two-thirds as wide as leaves on

unaffected trees. Diseased trees have a rosetted appearance due to the crowding

of leaves on twigs with shortened internodes. Affected trees have a darker

green color than normal.

Premature defoliation is not common. A variable number of normal

branches may be interspersed with affected ones on an infected tree (pi. 3, E).

14
VIRUS DISEASES OF STONE FRUITS 15

Figure 4,—A¡ Misshapen leaves with chlorotic areas from peach tree atfected with

rosette mosaic; B, comparable normal leaf.

Inoculation with buds from such normal-appearing branches did not result

in transmission.

Plum.—The Italian Prune variety of plum inoculated with rosette mosaic

virus showed symptoms simulating those of prune dwarf ( S 5 ). Infected

trees varied in response according to the form of the virus concerned, some

having strap-shaped leaves and others leaves that were only süghtly dwarfed,

roughened, and thickened. Wickson plum was slow to express symptoms but

had smaller leaves and definite rosetting in the third and fourth years after

inoculation. Damson plums did not express definite symptoms, but it is

perhaps significant that the nonvigorous trees in one orchard were the only

ones shown to be carrying the virus.

Diagnostic or Unusual Characteristics

The symptoms of rosette mosaic on peach have some similarities to those of

prune dwarf (X5), sour cherry yellows, and peach mosaic {114). Peach is

more severely affected by rosette mosaic than by prune dwarf, whereas Italian

Prune is less markedly affected by rosette mosaic and more severely affected

by prune dwarf. Rosette mosaic virus does not produce the dieback or ring

spot symptoms characteristic of the sour cherry yellows virus complex on

peach. In two cases of attempted transmission rosette mosaic virus did not

cause sour cherry yellows symptoms on Montmorency sour cherry. Sour

cherry yellows symptoms on peach are generally distributed throughout the

tree the year after bud inoculation, whereas the symptoms of rosette mosaic
16 HANDBOOK 10, U. S, DEPARTMENT OF AGRICULTURE

tend to be localized in a few branches during the first season. Rosette mosaic

has not resulted in color breaking of blossoms, in distortion of fruit, in shot

holes or emargination of leaves, or in the marked and general chlorosis frequently caused by peach mosaic virus (114),

Transmission

Transmission of the disease has been effected by grafting, by the transfer

of soil from diseased to healthy trees, or by planting healthy trees in a location

previously occupied by diseased trees. Transmission by means of soil has not

precluded the possibility of transfer by insect vectors, particularly the black

peach aphid (Anurapbis persicae-niger (Smith) ). Some 3 0 attempts to transmit the virus by means of such aphids, however, did not result in disease

expression.

Incubation Period

The incubation period has varied from a few weeks under optimum conditions in the greenhouse to 9 months and even as long as 21 months in the

field. The length of time required depends apparently on the virulence of the

virus, the susceptibility of the variety, and the state of tree growth during

the incubation period. When transmission with contaminated soil was started

by July 15, symptoms appeared 10 months later. Trees planted in diseased

soil in the spring showed symptoms the following spring, but trees planted in

the fall did not show symptoms until the second spring.

On seedlings 18 to 24 inches tall the shortest incubation period was 12 to

16 days when rapid-transmission techniques were used (86). With the

defohation technique 14 to 19 days was required for symptom expression

and with the shading technique 18 to 21 days (97),

Thermal Relationships

Hildebrand ^ was unable to inactivate rosette mosaic virus by soaking the

bud sticks in a hot-water bath at Î0° C. for 20 to 22 minutes.

Control Measures

Removal of diseased trees and avoiding replanting for several years after

their removal are indicated control measures. Peaches should not be planted

immediately after plums unless the plums are known to be free from rosette

mosaic. Plum varieties should be indexed for freedom from virus before being

used as propagating stock by nurserymen.

Remarks

A relationship between the causal viruses of rosette mosaic and prune dwarf

is indicated by the similarity of symptoms on peach and Italian Prune and

by their closely similar thermal relationships.

* HiMebrand, E. M. Correspondence with the author, 1948,
PHONY

By LEE M. HUTCHINS, L. C. COCHRAN, and WILLIAM F. TURNER

Names of the Disease

"Phony disease" and "phony peach disease" are the names that have been

used in recent hterature. In Georgia, where the disease was first discovered, the

names "pony peach" and "collar oedema" are sometimes used by growers.

"Phony" appears to be an adequate name for this well-known disease and is

employed in the present discussion.

Names of the Causal Virus

The following names have been applied to the virus of phony: "Phony peach

virus"; "peach virus 4," Johnson's classification; "Prunus virus 3 (Hutchins)

Smith"; and ^^Namis mirabilis Holmes." Under the Fawcett system of virus

nomenclature the virus might be named ^^Pni^nivir mirabilisJ^ Pending adoption of an international system of virus nomenclature, the authors prefer to use

the name "phony virus."

History and Geographic Distribution

The first-known observation of phony was made on two peach trees at

Marshallville, Ga., about 1885, by Samuel Rumph, who discovered and

introduced the Elberta peach variety. The dwarfed specimens were called

"pony trees" by Rumph and were regarded as a curiosity. Their number

increased, and by 1915 thousands of peach trees were known to be affected

in a limited district in central Georgia. Illustrated papers calling attention

to and describing the disease appeared in 1920 {167) and 1928 {107),

Research into the cause of phony was begun in 1921 by the Bureau of

Plant Industry, United States Department of Agriculture. A fairly exhaustive, well-illustrated account of the research and other information acquired

was published in 1933 {112)^ and is freely used in the present discussion.

Some of the more important information may be found in other publications

{109, 110),

In 1928 phony was definitely attributed to an infective virus {IOS). This

finding was announced at a Federal quarantine hearing in Washington, D. C.,

in the fall of that year, at which time the disease was known to have spread

over a large district in central Georgia and a smaller district in eastern Alabama.

As a result of the hearing, Federal Quarantine No. 67 was promulgated, effective June 1, 1929 {241) ; this restricted movement of peach and nectarine

nursery stock and peach roots within and from affected districts. Also in

1929 a Federal-State cooperative program for systematic survey and removal

of phony-diseased peach trees was inaugurated.

By 1932 about 3 5 million peach orchard trees had been inspected. The

disease had been found in all the South Atlantic States below Virginia, in all

the Gulf States, in Tennessee and Arkansas, and in a few locations in the southern parts of Oklahoma, Missouri, and Illinois {23 8, 253), Subsequent surveys,

from 193 3 to 1947, extended the district of known occurrence of the disease

in most of the States named and discovered the disease in Indiana, Kentucky,

' Publication now out of print.

17
18 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Maryland, and Pennsylvania. However, apparently the disease has now been

eradicated from these last four States and from some other States in the lightly

affected area, as indicated under Control Measures.

These extensive annual surveys established the general area of distribution of

phony as being in southeastern United States. The disease has not been positively reported elsewhere in this country or abroad.

Economic Importance

Phony is first in importance among virus diseases of peach in Georgia and

some others of the Southern States. About 1,657,877 phony-diseased trees

have been removed by control agencies since 1929.^ Previous to that time it

was estimated that over a million orchard trees had been ruined by the disease

in central Georgia.

Phony does not cause early death of the affected trees; but it induces marked

dwarfing of new growth and of fruits, and this results in a smaller crop of

peaches, most of which are undersized. The longer the tree has the disease, the

more pronounced this effect becomes. The bulk of the fruit from phony trees

falls in the smaller commercial grades or is graded out entirely. Trees that

contract the disease before the bearing age never come into profitable bearing,

and mature trees that have had the disease several years produce no commercial

crop of fruit.

Previous to the eradication campaign instituted in 1929, the potential destructiveness of phony was determined in several central-Georgia orchards,

where the incidence of diseased trees was recorded annually on orchard maps.

Where the disease was very prevalent and spread was rapid, it was not uncommon for half of the trees in an orchard to show the disease at the age of 6 to 8

years and for 99 percent to be affected at the age of 12 years. Under such

conditions the orchards are ruined at an age when they should be most

productive.

Host Range

So far as known, phony virus is limited to the genus Prtmus. Knowledge

of species susceptibility is incomplete, but the tests and observations reported

here have been made. Susceptible to natural infection are all varieties, races,

and hybrids of peach (P. pérsica) ; peach trees propagated on rootstocks of

other species, such as almond (P. amygdalus), apricot (P. armeitiaca), Japanese apricot (P. mume), David peach (P. davidiana), and hortulan plum (P.

horttdana) ; and seedlings of apricot, Japanese apricot, chickasaw plum (P.

angmtifolia), and Mexican plum (P. mexicana) (117). Trees of all the abovenamed species on their own roots are also susceptible to artificial inoculation

through root grafting with root pieces from phony-diseased peach trees. Also,

typical phony symptoms are produced on peach following root-graft inoculations from affected trees of the other species; the peach has been used in this

way as a test plant for verifying the presence of phony virus in the other

species.

Although no truly symptomless carriers of phony virus have been found,

the species that tend to produce bushy growth, such as chickasaw plum, are

much less strikingly affected by the disease than are those species that normally

produce vigorous, elongated branches. Where known diseased trees are growing beside known normal trees of such species, differences in growth characters

^ U. S. Bur. Ent. and Plant Quar., Div. Dom. Plant Quar. Phony Peacli and Peach Mosaic

Control Project Annual Reports. [Processed, unpublished.]
VIRUS DISEASES OF STONE FRUITS 19

and seasonal response may be clearly evident, whereas in thickets of wild seedlings visual identification of trees carrying the virus may be extremely difficult

and highly uncertain.

figure 5.—Af Six-year-old Elberta peach tree affected "with phony, shoTving the dense

shadcvr cast by the heavy, appressed foliage, Fort Valley, Ga. B, Comparable normal

tree in same orchard.
20 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Symptoms

The symptoms of phony are most striking when the trees are in full foliage

and in good vigor. With the onset of symptoms, the phony tree develops

shortened internodes, rather profuse lateral branches, and flattened dark-green

leaves, giving the appearance of compact, dense growth with luxuriant foliage.

Decided dwarfing of new growth results, and the periphery of the upper

crown tends to take on a uniform, rounded appearance (fig. 5). Phony trees

may live many years. However, after several years of the disease, the wood

appears brittle and there may be a notable dying back of the terminal twigs

and branches. Vigorous, new terminal growth cannot be forced. As large

limbs die or are broken down, they are not replaced and the tree takes on a

ragged appearance. Even on such trees the foliage tends to be characteristic

of the disease; that is, it is greener and flatter than that of normal trees. In

spring, phony trees flower and leaf out earlier than normal ones of the same

variety, and they hold their foliage later in the fall (fig. 6).

Figtire 6.—Four nursery peach trees of same age, photographed October 24, 1931,

Fort Valley, Ga.: A and D, Normal trees; B and C, trees affected with phony as a

result of a root-graft inoculation, showing d'ïvarfing and retention of foliage.

The fruits on phony trees are well formed and ripen a few days earlier than

normal fruits, but they are reduced both in size and in number per tree (fig. 7;

pi. 3, A, B). They may be somewhat poorer in flavor than normal fruits, but

they are generally more highly colored. Seeds from phony peaches average

smaller than normal seeds, but they give excellent germination and produce

normal seedlings.

Infection with phony virus does not induce spindling growth or rosetting,

does not cause yellowing, rolling, or spotting of leaves, and does not produce

lesions, galls, or hypertrophies.

Identification of the disease in the affected tree is made from the aspects of
VIRUS DISEASES OF STONE FRUITS 21

figure 7.—A, Commercial pack of best-grade (1%- to 2V4-inch diameter) Hiley

peaches from normal tree; B, similar pack of 1'/a- to 1 %-inch-diameter fruits from

a tree affected with phony.

the tree as a whole and should not be attempted from detached specimens.

Phony trees are most easily identified in cultivated orchards, where comparison

with vigorous normal trees of the same age and variety can be made. Identification of the disease in wild seedlings and in orchards of mixed varieties may

be difficult unless the symptoms are very pronounced. Pruning, fertilizing,

and cultivating in keeping with good horticultural practice will induce vigor

and growth that intensify symptoms and bring out strong contrasts between

the diseased and the normal trees.

All of the many peach varieties observed in the States where phony occurs

are susceptible to the disease, and there are no significant differences in symptom manifestation. In Prunus species that tend to produce bushy growth,

such as P. angustifolia, it has been possible to identify phony in artificially

inoculated trees by comparing them with normal trees of the same species,

where the two were growing side by side in nursery rows; but in thickets of

wild seedlings visual identification in place may be unsatisfactory. In such

cases, if identification is important, root inoculation of peach nursery test

trees should be resorted to.
22 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Chemical Identification Test

A useful confirmatory aid to identification of phony is provided by a simple

and rapid chemical test, easily applied in laboratory or field (112).

The test reagent is prepared by acidulating 100 cc. of absolute methyl

alcohol with 15 to 20 drops of concentrated, chemically pure hydrochloric

acid. The degree of acidity required varies somewhat with the source of the

alcohol and with the specimens. Absolute ethyl alcohol may be used, but it

may require higher acidulation and for a rapid test must be hot.

For the test, select unblemished, whole-root sections 4 to 6 inches long, with

a woody cylinder 0.5 to 0.75 inch in diameter, and remote from malformations

or injuries in the root branches from which the specimens are taken. Wash

the specimens, remove excess water, and cut entire transverse sections of

woody cyhnder 0.5 to 1 mm. thick and immerse them in a few cubic centimeters of the reagent in a flat container. Before the test the wood should be

white or nearly so, fresh, and in good condition throughout. If numerous,

well-distributed purplish spots up to 2 mm. in diameter show up against a

background of whitish or faintly purphsh wood after a few minutes in the

reagent, a positive test for phony is indicated (pi. 3, C, D). Parallel check

tests should be run on known normal roots. At the end of the test period for

phony root sections, the normal sections should still be free from color or

should show a fairly even purple tint with no tendency to localization in welldistributed, intensely purple spots. If acidulation is too strong or if the sections are allowed to remain too long in the reagent, the entire surface of the

sections (either normal or phony) may display a purple color.

In well-developed cases of phony it is usual for each suitable root to give a

good positive test throughout the year. In old cases of the disease, brown

flecks may occur in the wood. These will usually turn purple in the reagent,

and numerous additional purple spots will develop during the test. Only the

wood gives the test; the bark shows no reaction. In some cases phony stem

wood may show a positive reaction to the test, but it is much less satisfactory

than root wood.

The test as just described applies to the peach. Other Pnmus species may

give a somewhat variable reaction, the test being excellent in some, as in P.

davidiana, for example, and less striking in others.

Diagnostic or Unusual Characteristics

^ Several characteristics of phony are seldom encountered in other known

virus diseases of peach or other woody plants. The chemical test (pi. 3, D) is

specific for phony and is a valuable confirmatory aid to identification. Localization of the virus in the woody cylinder is very unusual and has been

reported in only one other case, namely, Pierce's disease of grape {106) in

Cahfornia. Phony appears to be the only virus disease of stone fruits in which

symptom manifestation in the shoot, regardless of whether or not the virus is

present there, develops only after the symptomless root system is thoroughly

invaded by the virus; the incubation period is about 18 months. Techniques

for proving suspected virus diseases of woody plants now should include use

of root grafts and of other graft inoculum containing Hving wood, especially

when transmission is not secured by bark or bud grafts.

Transmission and Natural Spread

The early work to determine whether the disease is infectious was confined

to^ the peach. In extensive trials over several years the disease was not transmitted by grafting scions or buds from diseased trees on normal trees, but it
VIRUS DISEASES OF STONE ERUITS 23

was transmitted when a diseased tree and a normal tree were united by a root

graft or when a whole-root section from a diseased tree was grafted on a root

of a normal tree. It was concluded from these results that the virus is confined to the root system of the diseased tree. New data ^ indicate that phony

virus occasionally exists in the tops or portions of the tops of affected peach

and plum trees.

When patches of root bark from diseased trees were grafted on the root or

the root collar of normal trees, the virus was not transmitted, whereas it was

invariably transmitted by root graftage when the inoculum consisted of living

bark and wood. In the peach, therefore, the virus is apparently locaUzed in

the woody cylinder (113), Attempts to transmit the disease by juice from

affected roots were unsuccessful, and transmission by root grafting was accomplished only when there was definite growth union. The theory was

advanced that for transmission of the virus by grafting it was requisite that

a bridge of new wood be formed to connect the woody cylinder of the inoculum with that of the tree undergoing inoculation.

Four species of Cicadellidae have recently been reported as vectors of phony

under experimental conditions (240). These species are Homalodisca triqtietra

(F.), Oncometopia undata (F.), Graphocephala versuta (Say), and Cuerna

costalis (F.). All are members of the subfamily Tettigellinae. The four

species, when feeding on peach, appear to limit their attentions to the twigs

and small branches, usually to 1- and 2-year-old growth. These observations

indicate that the virus is present at times in some portions of the tops of the

trees. Such information as is available on the feeding habits of the subfamily

to which these vectors belong is not at variance with the data suggesting a

localization of the virus in the woody cylinder.

In the light of these discoveries, which furnish valuable information important to the control procedures, renewed and extensive investigations combining

pathological, entomological, and horticultural aspects of the problem are being

carried out. A large part of this work is located at the United States Horticultural Field Laboratory, Fort Valley, Ga.

Incubation Period

The precise length of the incubation period of phony under conditions of

natural infection is not known. However, in young orchards planted with

known normal trees and surrounded by a heavy incidence of disease in older

adjacent orchards, none of the young trees develop the disease the first year.

An occasional tree, perhaps 1 in 200, may develop the disease at the end of the

second growing season; in 1 exceptional case the number exceeded 3 percent.

Under such favorable conditions for natural spread, ordinarily 3 to 5 percent

of the trees may develop the disease during the third growing season after

planting.

The incubation period of the disease in peach nursery or orchard trees

inoculated by root-piece grafts in late winter is ordinarily about 18 months.

Multiple inoculations of large trees may shorten the incubation period by a few

months. "When scions of peach and other species are grafted in the tops of

phony-diseased trees, the growth from the scion develops typical symptoms at

once. When dormant peach nursery trees are grafted by the taproot to large

roots severed from phony-diseased trees but otherwise undisturbed in the

^Hutchins, L. M., Cochran, L. C, Turner, W. F., and Weinberger, J. H. Recovery of

phony virus from the tops of certain affected peach and plum trees. (Manuscript in preparation, )
24 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

soiij the new growth from the nursery tree will display phony characters

immediately.

Symptoms of phony on the shoots of peach are apparently induced directly

by effects of the virus in the roots. Shoot growth from virus-bearing scions

grafted on healthy trees appears normal during the first year of growth but

usually becomes phony along with the remainder of the tree during the second

year. Until the major portion of the root system is invaded by the virus, the

symptom-provoking conditions apparently are not sufficiently developed to

induce symptoms and terminate the incubation period. As soon as symptoms

appear in the shoot, all root pieces taken from a diseased tree will transmit the

disease, whereas a few months before the termination of the incubation period

many of the root pieces will not transmit the disease.

Thermal Relationships

Phony virus can be inactivated in dormant peach nursery trees 1 year after

root-graft inoculation by immersing the trees for 40 minutes in water maintained at 48° C. (12 6).

Control Measures

After the discovery in 1928 that phony is caused by an infective virus,

control activities were instituted through quarantine regulations and a program

for eradication of diseased trees.

Effective June 1, 1929, Federal Quarantine No. G7 (241) forbade the

movement of peach and nectarine trees or peach roots of any variety of tree or

ihrub grafted on such roots from regulated districts to any other part of the

United States except under a special permit from the United States Department

of Agriculture. Such permits were issued only if the nursery and its environs

for a radius of 1 mile had been inspected by Federal or State inspectors and no

phony had been found within the locality for at least 2 years. The Federal

quarantine was revoked in 1934. At present the movement of susceptible

nursery stock is controlled by uniform State quarantines. The requirement fo

certification is that any phony trees found within the 1-mile environs of the

nursery must be eradicated prior to June 3 0 of the current year. As a result

of intensive control activities, phony has been eradicated from the districts

producing most of the peach nursery stock in the Southeast.

Phony peach eradication was originated by the Bureau of Plant Industry in

1929, the work being carried out in cooperation with State agencies and property owners. The initial activities established the approximate boundaries of

the whole affected area, and the districts of heavy, general, moderate, and light

infestation. The program of orchard inspection and diseased-tree removal

that was inaugurated soon resulted in a marked decrease in the total number

of phony trees (23 8, 239).

In 1934, in keeping with a general plan of reorganization that was effected

at that time, direction of the phony peach disease control project was transferred from the Bureau of Plant Industry to the Bureau of Entomology and

Plant Quarantine, United States Department of Agriculture. Activities expanded in succeeding years with the aid of special allotments and increased

State cooperation. Progress of the work is extensively treated in a series of

annual reports ^ and in special publications (^2, 74, 75, 23 8). Phony has now

been found in 17 States, 10 of which have been much less heavily infected

than the others. By 1944 no phony had been found during three or more

^ See footnote 6, p. Í8.
VIRUS DISEASES OF STONE FRUITS 25

consecutive years in Indiana, Kentucky, Maryland, North Carolina, Oklahoma,

Pennsylvania, and Illinois. In Mississippi, Tennessee, Texas, Missouri, Louisiana, Arkansas, and South Carolina the incidence of diseased trees was drastically

reduced from a total of 13,415 affected trees in 1936 to a total of 1,724 affected

trees in 1946, and the disease has apparently been eliminated from a large

number of counties.

After initial decrease in some districts, however, further reductions proved

more difficult. Several factors served to handicap the control activities rather

severely. Among these are the long incubation period and the lack of knowledge as to the time of year when natural spread takes place most rapidly. It

may well be that until eradication of diseased trees can be supplemented by

other means of control, the most that can be hoped for in some of the rapidspread districts is a maintenance of status quo.

The work is continuing under an enlarged program as a portion of a project

entitled "Phony Peach and Peach Mosaic Control" under the general direction

of the Division of Domestic Plant Quarantines, Bureau of Entomology and

Plant Quarantine, United States Department of Agriculture, Gulfport, Miss. '^

^ The project leader, A. E. CavanagK, maintains headquarters at Room Î23, Federal Building, San Antonio, Tex. Local ofiSces are maintained in several other States.

891793 o—îl~3
PEACH MOSAIC

By LEE M, HUTCHINS, E. W. BODINE, L. C. COCHRAN, and GILBERT L, STOUT

Name of the Disease

The name ''peach mosaic"' was appUed to the disease in 1932 by Hutchins

(111), because of the similarity of its symptoms to those of mosaics well

known on other plants. At that time this name served to distinguish the

disease from the other virus diseases affecting peach, and it was not foreseen

that other distinct diseases of the mosaic group would be found on stone fruits.

Since "peach mosaic" is now recognized as the common name of this specific

disease, others of the group in which mosaic is incorporated in the name should

be distinguished by qualifying adjectives or by new names of which mosaic

is not a part.

Names of the Causal Virus

The virus causing peach mosaic has been variously named. The chronology

of the names is as follows: Peach virus 6, Johnson's classification; Prunus virus

5 (Hutchins) Smith; Marmor persicae Holmes; and FlavimactUa persicae

(Holmes) McKinney. Under the Fawcett system the name might be

^^Primivîr flavimacula.'^ Until more complete agreement is attained, it is the

preference of the authors to refer to the causal virus by adding the term ''virus"

to the common name of the disease; thus, "peach mosaic virus."

History and Geographic Distribution

In July 1931 W. F. Turner ^^ called Hutchins' attention (114) to a new

disease on peach at Bangs, Tex., subsequently named "peach mosaic." At

about the same time Bodine (3 0, 31), observed seven affected trees near

Palisade, Colo. Extensive surveys (227)^^ by State and Federal agencies have

shown that the disease exists in southern California, southern Utah, Arizona,

New Mexico, southern Oklahoma, western Arkansas, western Colorado, Texas,

and Mexico.

The widespread existence of the disease in the Rio Grande Valley is evidence

that it had been present there for a long time. It is plausible that the causal

virus could have been carried from there in nursery stock, especially in wild

plums, in which hosts symptoms are usually absent, to sections where peach

varieties, cultural practices, and environment made its presence more evident.

Both the pottawattamie, or wildgoose, plum (Pnmus iminsoniana) and the

American plum (P. americana) are common in the Rio Grande Valley, where

they have been planted along ditchbanks. The fruits are prized for jelly, and

plants have been moved as sucker shoots from one locality to another. Index

tests performed by budding onto peach have shown that a high percentage of

the wildgoose-type plums in certain localities and occasional trees of the

American plum are infected.

Economic Importance

The loss from reduction in quality and quantity of fruit due to the effects

of the peach mosaic virus is sufficient to make culture of peach varieties as

^^ In charge of the phony peach eradication campaign, U. S. Bureau of Plant Industry.

^^ U. S. Bur. Ent. and Plant Quar., Div. Dom. Plant Quar. Phony Peach and Peach

Mosaic Control Project Annual Reports. [Processed, unpublished.]

26
VIRUS DISEASES OF STONE FRUITS 27

severely damaged as J. H. Hale, Elberta, and Rio Oso Gem unprofitable.

Others of the freestone group, particularly those having J. H. Hale or Elberta

heritage, also are severely damaged. Some varieties, including most of the

clingstones and several of the freestones, even though mosaic variably reduces

their yields, are sufficiently tolerant to produce profitable crops. Such varieties

when carrying severe symptom-producing forms of the causal virus are hazardous to less tolerant varieties in mixed or adjacent plantings.

Damage from the disease is nearly negligible on plums, prunes, apricots, and

almonds in southern California, but little is known of its effects on these hosts

in sections with other climates. In cooler sections fruits on some affected

apricot trees were observed to be very bumpy and worthless. The fruits on

certain almond trees were bumpy, but there was no reduction in yield or

quality of the nuts.

Host Range

Extensive studies indicate that the host range of the peach mosaic virus is

limited not only to the genus Pnmus but also to certain species and even to

certain horticultural varieties within the genus. Further specification is indicated by the fact that individual horticultural plum varieties were found

susceptible to one form of the virus but immune from others. The cherry and

cherrylike species generally appear to be immune. The following species have

been experimentally infected: Peach (P. pérsica); nectarine (P. pérsica var.

nectarina) ; almond (P. amygdahis) ; apricot (P. armeniaca) ; domestica plum

(P. domestica) ; Japanese plum (P. salictna) ; Japanese apricot (P. mume) ;

David peach (P. davidiana) ; damson plum (P. insititia) ; American plum

(P. americana) ; chickasaw plum (P. angustifolia) ; wildgoose, or pottawattamie, plum (P. munsoniaita) ; myrobalan plum (P. cerasifera) ; Mexican plum

(P. mexicana) ; Bessey cherry (P. besseyi) ; tangut almond (P. tangtUica) ;

and Manchu cherry (P. tomentosa). All attempts to infect sweet cherry (P.

avium^) varieties growing on mazzard or mahaleb rootstock and mazzard

(P. avium) seedlings, mahaleb cherry (P. mahaleb), sour cherry (P. cerasus)

growing on mahaleb rootstock, western chokecherry (P. virginiana var.

demissa), desert apricot (P. fremontii), desert almond (P. fascicîùlata), and

hollyleaf cherry (P. ilicifolia) have failed.

The peach mosaic virus has been recovered from many naturally infected

horticultural varieties of peach including flowering types. It has also been

recovered from naturally infected French (Agen) prune, several varieties of

apricot, and a few varieties of Japanese plum growing in orchard formation.

The virus has been recovered from naturally infected wild pottawattamie

(wildgoose), chickasaw, American, Mexican, and myrobalan plums; Japanese

apricot, David peach, tangut almond, Bokar plum (P. bokbariensis), hortulan

plum (P. hortîdana), flatwoods plum (P. tcmbellata), and hog plum (P.

reverehonii). Recovery from Japanese plums has been rare and limited to

certain varieties such as Maynard (36), Becky Smith, Flaming Delicious, and

Cain Seedling. Attempts at experimental infection indicate that some varieties

of both Japanese- and domestica-type plums are variably affected with or

immune from some or all of the forms of the peach mosaic virus. Chickasaw

plum is an important host reservoir of the virus in Texas, where it exists in

extensive thickets and has been found generally infected, but without symptoms, in the vicinity of mosaic-infected peach orchards. The pottawattamie

plum, likewise, has been found to be a common reservoir of the virus in New

Mexico, Arizona, and Utah, where it has been planted along irrigation canals
28 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

and fences. Escape seedlings of cultivated plums forming thickets along

fences and irrigation canals in New Mexico have been found generally infected.

Symptoms

Peach.—Symptomatology of peach mosaic is made complex by the presence

of many causal virus forms (32, 3 5, 60, 61, 115), some of which produce

symptoms so mild that diagnosis is difficult and others of which produce ruinous effects on peach varieties like J. H. Hale. Given enough sources of the

virus, a gradient in symptoms can be produced (57). Further, the disease

has been observed to proceed in a sequence of acute followed by chronic phases

in which infected trees show strong symptoms and later appear to recover

partially (56).

On J. H. Hale peach trees inoculated the previous fall and, similarly, on

orchard trees showing first-year symptoms, spring growth is variously retarded;

Figure 8,—Leaves of Early Wheeler peach, a partially tolerant variety, showing summer symptoms of peach mosaic.
VIRUS DISEASES OF STONE FRUITS 29

Figure 9.—A and B, Peach shoots severely affected, "with peach mosaic, showing (A)

small, deformed leaves and retarded foliation in spring and (B) rosetting and

shortening of growth in midsummer; C, unaffected peach shoot in spring.
30 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

retardation corresponds to the virus form involved (pi. 4, D). On severely

affected peach trees, early-formed leaves may wither and fall or may assume

irregular shapes and be variously mottled (fig. 8). On some trees the initial

symptoms are small yellow flecks adjacent to veinlets (veinlet clearing) ;

necrosis and dropping of tissue or whole leaves may be evident later. Usually

Figure 10,—A, Orchard Elberta peach tree affected with peach mosaic, in summer;

Bj comparable unaifected tree.
VIRUS DISEASES OF STONE FRUITS 31

succeeding leaves on such trees are variously and strikingly mottled by irregular patterns of yellow and yellow green (pi. 4, C). Mottling of the severe

figure 11.—J. H. Hale peach trees artificially infected with peach mosaic virus: A,

With retarded foliation the first spring after inoculation; B, dwarfed, but without

retarded foliation, the second spring after inoculation. C and D, Comparable

unaffected trees.
32 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

type is usually accompanied by distortion and reduction in size. On mildly

affected trees both mottling and distortion of leaves are less pronounced. The

degree of mottling, presence of veinlet clearing, and amount of leaf distortion,

retardation, and dwarfing appear to vary with different forms of the virus;

thus the total effect on the tree varies. Some forms produce brilliantly

mottled patterns, but fail to dwarf trees as much as others which produce less

mottle. With some forms only scattered leaves may be affected, but these may

be distorted and brilliantly mottled, whereas with others the majority of the

leaves may be affected, but only mildly mottled and distorted.

As the season progresses, trees in the first year of the disease tend to become

greener in contrast with normal than they were early in the season {46, 114),

The probable reasons are that growing conditions are more favorable for the

host and possibly conditions are less favorable for the virus. Succeeding shoot

growth is less than normal (fig. 9), and affected trees become variably

dwarfed {^g. 10), dwarfing corresponding to the severity of spring symptoms.

By the second year, diseased trees show less shock in the spring and appear to

go into a chronic stage of the disease (fig, 11). In this condition trees have

more leaves than during the acute stages of infection, yet they show welldeveloped mottle, reduced shoot growth, and other symptoms corresponding

to the form of the virus with which they are affected. The veinlet-clearing

symptom occurs only on leaves on newly infected shoot growth and does not

recur in growth diseased more than 1 year.

On varieties severely affected the fruits are usually small, bumpy, and misshapen (pi. 4, B). The bumps usually develop coincidentally with the stonehardening stage. On less damaged varieties the fruits are smoother. Virus

forms producing only mild effects, even on varieties like J. H. Hale, do not

make the fruits bumpy.

Another striking effect of the peach mosaic virus is the production of white

spots and streaks in the pink color in flowers of varieties having large, showy

pink flowers (pi. 4, A). These spots are boat-shaped, and the larger have pink

centers. The overlapping and variation in size of spots produce the appearance

of variously shaped streaks and splashes. Such color patterns have not been

seen on varieties having small or intermediate-sized flowers.

The amount of damage caused by peach mosaic to peach depends largely

upon two factors—the form of the virus involved and the tolerance of the

peach variety. Peach varieties may be divided into three comparative classes

according to the degree they are damaged by forms which produce severe

effects on the J. H. Hale variety. The most important commercial varieties

are classified in table 1. Virus forms which produce only mild symptoms on

J. H. Hale may exist without symptoms in less damaged peach varieties.

Other hosts.—Symptom expression on apricot, almond, myrobalan plum,

Japanese apricot, American plum, chickasaw plum, Bessey cherry, Manchu

cherry, and certain varieties of prunes and Japanese-type plums is sufficiently

uniform for them to be treated as a group. On these hosts some forms of the

peach mosaic virus make brilliant symptom patterns of rings and oak-leaf,

splotchy, and irregular-shaped mottles. Others produce patterns similar to

these in outline but less brilliant in intensity, while still others produce infection without any symptoms. Given enough sources of the virus, a symptom

gradient for these species can be formed, ranging from no symptoms to brilliant, similar to that occurring on peach but without specific correlation with

the effects on peach; that is, forms producing striking mottle on apricot may
VIRUS DISEASES OF STONE FRUITS 33

TABLE 1.—Classification of peach varieties according to the relative severity

of their reaction to peach -mosaic

Severely damaged varieties Medium-damaged varieties Slightly damaged varieties

Afterglow Admiral Dewey Andora ^

Ambergem Alexander Australian Saucer

Belle Babcock Carolyn ^

Bonita Brackett Cortez ^

Dixigem Carman Curry

Dixired Champion Erly-Red-Fre

Duke Hale Cumberland Fisher

Early Halehaven Early Elberta Gaume ^

Elberta Early Rose Greensboro

Fay Elberta Early Wheeler Halford No. 2 ^

Fireglow Eclipse Johnson ^

Gage Elberta Fair Beauty Lukens

Golden State Fortuna^ Mikado

Goldeneast Fredberta Orange Cling ^

Goldenglobe Golden. Jubilee Paloro ^

Halberta Halehaven Peak^

Hiley Herb Hale Phillips ^

Illinois Jerseyland Shasta ^

J. H. Hale Krummel Sims^

Kalhaven Lizzie Stanford ^

Late Elberta Lucas Beauty Stuart ^

Loring Newday Sullivan No. 1 ^

Meadow Lark Ozark Sullivan No. 2 ^

Nectar Redelberta Sullivan No. 4 ^

New Jersey State Rose Redskin Sungold

Pacemaker Rochester Tudor ^

Prairie Rambler Southland Tuskena (Tuscan) ^

Raritan Rose Valiant

Redhaven Walton ^

Rio Oso Gem Williams '

Roberta Zuni

Shippers Late Red

Sunday Elberta

Sunhigh

Vedette

Veteran

White Hale

Wilma

^ clingstone.

produce severe or only mild symptoms on peach and conversely. In general,

the degree of symptom production on apricot (fig. 12, A) and on almond

{iig, 12, B) by the various virus forms corresponds to the behavior of these

forms on the other hosts in this group. Exceptions are certain varieties of

cultivated plums and prunes, some of which develop symptoms with the

apricot-symptom-producing forms, but not with those forms which fail to

mottle apricot. Some plum varieties can be infected and retain any of the

virus forms without symptoms. Some plum varieties appear immune. Plum

and prune varieties that develop symptoms are Becky Smith, Beauty, Shiro,

Flaming Delicious, Cain Seedling, French (Agen) (fig. 13), and Standard.

Transmission and Incubation Period

Transmission of the peach mosaic virus has been effected experimentally

from peach to peach by tissue grafting with the following tissues: Fruit,
34 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

figure 12.—Leaves of (A) Royal apricot and of (B) Ne Plus Ultra almond affected

with peach mosaic. Unaffected Ne Plus Ultra almond leaf at lower right.

leaf, Stem wood, stem bark, root wood, and root bark {63). It thus appears

that nearly all the tissues of a peach tree are invaded. If scions of diseased

tissue are grafted on healthy trees at the time of breaking of dormancy, transmission may result in as short a period as 14 days. If grafts are made when

the leaves are partially expanded, the incubation period may be as long as 6

weeks; and if they are made as late as June, symptoms do not usually appear

until the following season. Kunkel (Í33) showed that a minimum contact

of 2 days between diseased and healthy tissues made at the cambium is needed

for transmission to take place.

Spread in nature has varied with locality and is assumed to be through an

insect vector. Little is known of the incubation period after infection

under natural conditions. Bodine {3}) reported a case in which seedlings

planted in the spring showed symptoms in August. He assumed that they

were probably infected in April or May.
VIRUS DISEASES OF STONE FRUITS 35

Figure 13.—Leaves of French (Agen) prune affected with peach mosaic.

leaf ac lower left.

Unafiected

Thermal Relationships

Heat treatments of infected peach trees and bud sticks were not effective

for the cure of peach mosaic, whereas similar treatments inactivated the

viruses of peach yellows, peach rosette, little peach, and red suture (132).

Control Measures

The control of peach mosaic was first initiated as an eradication program.

Later, survey results showed the disease to be widely existent, especially in noncommercial and marginal sections. In some districts the combined cost of

inspection, removal, and loss from removal of trees of slightly damaged varieties overbalanced the economy of protection of newly planted orchards. In

these districts growers are limited in the choice of varieties to those which

tolerate mosaic with little damage. In some districts where growers desire

Elberta and other nontolerant varieties, spread is being effectively held down

by removal of infected trees. Removal is coordinated with a nursery-inspection and quarantine procedure for prevention of further spread through

nursery stock within the infected districts and to sections outside.

Remarks

The peach mosaic virus comprises a group of many extremely variable forms

which produce a wide range of symptoms that are very hard to delimit (32,

57, 64). New forms, the interaction of which appears to depend on their
36 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

relationship, seem to be arising continually. Symptom expression is further

complicated by the varietal reactions of the hosts. A given form of the virus

will produce symptoms ranging from mild on one host to severe on another.

Conversely, on a given host there will be a range of symptoms because one

form of the virus produces mild symptoms and another severe. A person without experience might confuse with peach mosaic certain other virus diseases of

the mosaic group, especially those caused by some forms of ring spot virus

during the spring season, peach mottle, and yellow bud mosaic.
X-DISEASE 12

By E. M. STODDARD, E. M. HILDEBRAND, D. H, PALMTTER, and K. G. PARKER

Other Common Names of the Disease

The disease has also been called eastern X-disease, yellow-red disease, yellowred virosis, and eastern yellow-red virosis.

Names of the Causal Virus

Marmor lacerans Holmes; Carpophthora lacerans (Holmes) McKinney.

History and Geographic Distribution

X-disease was first reported on peach in Connecticut in 1933 (216), but

reports from growers indicate that it had been present several years previously.

The status of the disease in Connecticut from 1933 to 1939 was discussed by

Stoddard {216, 217, 218, 219, 220, 221, 222). The disease was identified in

Massachusetts and New York in 1938 (41, 99), in Ontario, Canada, Michigan,

and Pennsylvania in 1941 {6, 48, 158), and in Ohio in 1944 (78).

X-disease has been reported on chokecherry in Connecticut (222), IlHnois

(1, 203), Indiana, Maine, Massachusetts (42), Michigan, New Hampshire,

New York (100), Ohio, Pennsylvania (268), Rhode Island, Vermont, and

Wisconsin (222) and in Ontario.

In New York growers reported that the disease was present on cultivated

sour cherries as early as 193 8. The disease was observed by Palmiter in 1942

and detailed inoculation studies were begun in 1946. Transmission to sour

cherry was reported by Palmiter and Parker (171). X-disease has now been

found in at least 36 cherry orchards located in 7 counties, but no definite

survey has been conducted. It has been found in 1 Michigan cherry orchard,

but its full extent on cherry in that State has not been determined.

On cultivated sweet cherry the disease has been observed with certainty on

the Windsor variety in eight orchards distributed in three counties in New

York and on the Bing variety in one orchard. It was considered severe in

three of these orchards. Bud inoculations made from the Windsor variety to

peach seedlings resulted in the development of characteristic symptoms of

X-disease.

Economic Importance

X-disease is a major disease of peach in Connecticut, Massachusetts, and

New York. It is present and potentially important in Michigan and Pennsylvania, but it is not considered of importance in Ontario, where few chokecherries are growing adjacent to peach plantings. Affected peach trees of

bearing age become commercially worthless in 2 to 4 years. The younger the

tree the more severe and rapid the development of the disease; consequently,

trees infected at 3 years of age or less rarely produce fruit. Infected cherry

trees soon become worthless for fruit production. In certain New York

orchards up to 50 percent of the EngUsh Morello trees are not bearing as a

result of this disease, and the disease has made many Montmorency trees unprofitable in other orchards.

^^ The description of symptoms and other characteristics applies to X-disease as it occurs in

eastern United States.

37
38 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Host Range

Symptoms are produced on all observed varieties of peach (Primus pérsica)

(102); on purple-leaved peach (?. pérsica var. atropurptirea); on nectarine

(P. pérsica var. nectarina) ; on chokecherry (P. virginiana) ; on almond (P.

amygdalns) ; on wildgoose plum (P. munsoniana) ; on Chinese bushcherry

(P. japónica); on Bessey cherry (P. besseyi) (223); on cultivated sour cherry

(P. cerasus) varieties Montmorency, English Morello, and Chase; on mazzard

(P. avium) seedlings; and on sweet cherry (P. avitim) varieties Windsor and

Bing. Other Frumts spp. are suspected of being hosts, but studies have not

been completed. Kunkel (13 6) demonstrated transmission of the virus to and

the production of symptoms on various herbaceous plants: tomato (Lycopersicon esculenttim), carrot (Daucns carota), parsley (Petroselimim crispum),

and periwinkle (Vinca rosea).

Wild American plum (P. americana) has been infected, but developed no

visible symptoms. Wild black cherry (P. serótina) and beach plum (P.

maritima) did not retain the virus after inoculation and were thus determined

to be immune.

Symptoms

Peach.—Foliage of affected peach trees appears normal in the spring for

about 7 weeks after growth starts; then suddenly a diffused and blended yellow

and red discoloration, frequently accompanied by a longitudinal upward

rolling of the leaf edges, appears. The discolored spots may occur anywhere

on the leaf blades, are irregular in shape and size, and vary in number from

few to many. At ñrst the spots appear water-soaked, but soon they exhibit

the characteristic coloration of blended red and yellow. Simultaneously the

remainder of the leaf blade becomes chlorotic. The leaves become brittle; and

the discolored areas usually fall out without necrosis, giving a characteristic

tattered appearance to the foHage. Eventually affected leaves except the tip

ones drop; the tip ones are retained to the end of the growing season (pi. 5).

On greenhouse-grown peach trees leaf rolling, chlorosis, and stunting of

growth are very marked but spotting, tattering, and defoliation are less than

on trees grown out of doors. This is also true of seedling trees grown from

so-called wild pits in the greenhouse or out of doors. Purple-leaved peach shows

chlorosis and bleaching of the purple color and finally exhibits a blotchy

yellow-green and purple coloration.

The fruits on affected parts of trees usually shrivel and drop soon after

the foliage symptoms appear. The occasional fruits remaining on the trees

ripen prematurely and are unpalatable in flavor, and seeds do not develop

within the pits. Fruits on healthy growth of infected trees are unaffected.

Trees of bearing age are usually not completely infected at one time;

rather, the affected twigs and branches are scattered indiscriminately over the

tree, standing out in sharp contrast with the healthy portions of the tree.

Viewed from a distance, infected trees have a distinctly hghter color than

adjacent healthy trees. The infected, defohated branches are undoubtedly

weakened and consequently suffer from winter injury, resulting in a certain

amount of dieback. Young trees usually die after infection, but old trees

may live indefinitely.

Chokecherry.—In the first year of infection the foliage of chokecherry

(pL 6, E) shows dull to brilliant yellow, orange, and red coloration of the

foliage by mid-June—6 or 7 weeks after growth starts—intensifying with the

season and reaching its height in August. The briUiant foHage colors in the
VIRUS DISEASES OF STONE FRUITS 39

prevailing green background of the countryside in summer can be seen for

considerable distances. In the second season of infection the symptoms are

different. The leaves have a duller color, and stunted growth or rosettes

appear on some of the terminals; such growth has leaves much smaller than

normal, abnormal in shape, and often very rugose at the shoot tips. By the

third season the most conspicuous symptoms are the duller colors and the

terminal rosettes, on which dark green prevails. Death follows this advanced

stage.

Diseased chokecherries may blossom; but most, if not all, of the ovaries

abort at an early stage. The fruits which are retained at the end of the

season do not mature and have undeveloped flesh and always dead seeds in the

pits. When grown in the greenhouse, infected chokecherries show the advanced rosette stage of disease that frequently results in death during the

second growing season.

Sour cherry.—In New York {171, 172, 173) X-disease has been transmitted from cherry to cherry, from cherry to peach, and from chokecherry

to cherry. The disease is characterized by many different symptoms apparently resulting from a complication of factors, including varietal differences,

the influence of rootstock, soil conditions, and seasonal temperature variations.

The possible complex association of other viruses is also considered. Generally

speaking, the disease is difficult to diagnose by foliage symptoms alone. The

rootstock on which a variety is propagated plays an important part in symptom

expression.

The symptoms on Montmorency on mazzard rootstock show first on a

single branch which bears cherries of smaller size than normal, of lighter

color, and frequently pointed (pi. 6, A, B). Some normal fruits are usually

interspersed on portions of the same branch, especially during the first year.

Figure 14.—Montmorency cherry trees affected w^ith X-disease: A, Tree that had

^Ited 3 to 4 weeks before being photographed; B, tree just beginning to wilt.
40 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

The disease increases progressively each year throughout an individual tree

until finally most of the fruits fail to reach maturity. There is also a tendency

toward rosetting of the shoots and a generally pale foliage.

The same uneven ripening of fruits of Montmorency on mahaleb rootstock

is apparent, but less noticeable. In midseason the symptoms may include

wilting of foliage, and later in the summer on some trees they may include

decline in vigor (fig. 14). Young trees on mahaleb rootstock respond to

inoculation with a rather rapid wilt and decline in the first season after

inoculation. Mature trees on mahaleb rootstock which wilted in midsummer

and showed dead leaves by fall were found to have a large proportion of dead

roots. Root death proceeded progressively from the distal end toward the

base, with dead bark overlying live wood. In contrast, roots dying from

winterkilling or wet feet showed root injury initiated largely from the proximal

end and progressing toward the tips, with wood discolored under live bark.

The symptom pattern of immature fruits of English Morello on mazzard

rootstock follows that of Montmorency. However, the fruits are less pointed

and more spindle-shaped. The fruits on diseased trees have a tendency to

drop early. After a few years few or none remain on the diseased trees at

harvesttime. Diseased trees of English Morello growing on mahaleb rootstock

show wilt and decline and die rather quickly without the other symptoms

developing to any marked degree.

Young English Morello on mahaleb rootstock when infected artifically wilts

and declines as does Montmorency. When it was on mazzard, in one experiment a rosette type of growth (fig. 15), as observed on trees in the orchard,

developed in the second year.

Sweet cherry.—So far, observations have been made on infected cultivated

sweet cherry during only 1 year and in a relatively small number of orchards.

Figure 15.—A, Shoots from English Morello cherry tree affected with X-disease, showing rosette type of growth; B, comparable unaffected shoot.
VIRUS DISEASES OF STONE FRUITS 41

Therefore, the description of symptoms on that host is subject to revision; but

at least part of the symptom complex seems rather well defined.

Diseased trees of the Windsor variety on mazzard rootstock bear fruits that

fail to mature, are Hght red in color, are somewhat pointed longitudinally, tend

to be angular in cross section, and are much smaller than normal (pi. 6, C, D),

Any portion of the tree, from one small branch to the entire tree, may be

affected. Sometimes a branch with nearly all the fruit affected may be

adjacent to a branch with a good crop of normal fruit. Shoot growth on

affected branches tends to be shorter than normal. Late in the fall, part of

the leaves on such branches may exhibit a yellowish-bronze color along the

midrib. Fruit symptoms on the Bing variety were similar but less pronounced.

Diseased trees on mahaleb rootstock have not been observed to exhibit any

of the symptoms just described. They may wilt in midsummer or develop

various degrees of decline. Part or all of the roots on such trees are dead, and

frequently there is a sharp line between dead and live bark at the bud union.

Bessey cherry.—The foliage symptoms on Bessey cherry are somewhat similar

to those on chokecherry, but the colors are less brilliant and conspicuous. The

entire plant, including the foliage, is severely stunted, and there is no significant perforation or dropping of foliage. Bessey cherry does not show the

successive yearly stages of disease development as described for chokecherry.

Wildgoose plum.—^Light- and dark-green mottling of foliage is followed by

dull-red coloration, with no perforation or dropping of foliage.

Nectarine and almond.—The symptoms approximate those of peach.

Chinese bushcherry.—The foliage is stunted, rosetted, and chlorotic; and the

plants have an unthrifty appearance.

American plum.—The symptoms are so mild that usually they are not

visible.

Diagnostic or Unusual Characteristics

Symptoms do not appear on peach and other hosts until mid-June. Order

of appearance of symptoms on peach is the same year after year—spotting,

chlorosis, shot hole, and defoliation. On chokecherry the symptoms change

from year to year, consisting of brilliant red to yellow coloration of foliage,

duller coloring and resetting, and finally resetting and death—the sequence

usually appearing in successive years with some overlapping. Diseased chokecherry shrubs must be within about 200 feet of peach trees for infection to

spread naturally to peach.

Transmission

X-disease has been transmitted with buds, bark patches, and scions, but not

with expressed juice. The virus has not been transmitted in winter from

outdoor trees except by root-bark patches. Transmission has been made

with Cusctita campestris Yuncker from peach to herbaceous plants, but the

reverse has not been accomplished: In 1944 Kunkel {13 6) reported transmission from peach to tomato, carrot, parsley, and periwinkle, and in 1945

Hildebrand (93) reported transmission from peach to tomato. Spread from

peach to peach or peach to chokecherry apparently does not occur or is rare

in nature. Insect transmission apparently has been effected in a few instances,

but it is not yet considered to have been satisfactorily demonstrated. A leafhopper similar to Scaphytopius (Cloanthamis) acuHis (Say) is the suspected

vector.

Incubation Period

Symptoms comparable with those which usually appear after natural
42 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

infection in the orchard can be induced on peach in the greenhouse or out of

doors in 3 to 6 weeks by bud inoculation. A simple pruning technique or other

means such as defoliation, girdling, or shading may reduce the interval between

moculation and visible symptoms (83, 86, 97), The virus becomes established

in the tree within 6 or 7 days after inoculation and can be transmitted for

some time before symptoms appear.

Thermal Relationships

Hildebrand found that the virus is inactivated in bud sticks of peach by

immersion in water at 50° C. for 6 to 7 minutes. A range of treatments from

48.5° for 16 minutes to 53° for 2 minutes in water completely inactivated the

virus without significant injury to the buds in Stoddard's experiments.

Control Measures

Spread of X-disease can be stopped or prevented in peach by complete

eradication of chokecherry to a distance of 5 00 feet from peach orchards (170),

A distance of 100 feet gives good commercial control. New orchards and

nursery plantings of peach should be started at least 5 00 feet from chokecherry

and preferably from all other wild species of Pmnus. Removal of diseased

peach trees is ineffective as a control measure. Eradication of chokecherries is

accomplished better by the use of herbicides than by cutting or grubbing out

the bushes. Ammonium sulfamate (Ammate) or sodium chlorate sprays

applied when the plants are in full leaf at a concentration of % to 1 pound

per gallon of water are effective (107, 103, 169). Sodium chlorate is inflammable, and great care must be taken in using it. Therefore, commercial

formulations of this chemical, such as Atlacide, should be used as directed by

the manufacturers.

Chemotherapeutical treatments on X-disease-infected peach have been

successfully used. Quinhydrone, and other chemicals to a less degree, inactivated the virus in peach bud sticks soaked in water solution of each of the several chemicals {224), Water solutions of several chemicals injected into the

trees or watered on the soil of potted peach trees after inoculation prevented the

appearance of symptoms. Notable among these was ^-aminobenzenesulfonamide; ^-toluenesulfonamide, hydroquinone, maltose, calcium chloride,

and zinc sulfate also gave satisfactory results {22'), 226).

Remarks

The similarity of symptoms on peach suggests a very close relationship of

the X-disease and western X-disease. The recent reports of Palmiter and

Parker {171) and of Richards, Hutchins, and Reeves {198) that both diseases

occur on sour cherry further suggest that they are very similar if not identical.

The sharp difference between the symptoms of infected trees on mazzard and

mahaleb rootstocks is strikingly similar to that associated with buckskin of

sweet cherry in California.
WESTERN X-DISEASE

By E. L. REEVE.S, EARLE C. BLODGETT, T. B. LOTT, J. A. MILBRATH,

B. L. RICHARDS, and S. M. ZELLER

Names of the Disease

Several common names have been applied to the disease caused by the

western X-disease virus on different hosts. '^Western X-disease" was appHed

originally to the disease as expressed on peach (188), and it has been used in

referring to the disease on western chokecherry. In Utah western X-decUne

also has been used for the disease on peach. Red-leaf and western X red-leaf

(201) have been applied to the disease on western chokecherry.

Wilt and decline (196, 199), western X wilt and decline, and decline and

dieback of sour cherry have been applied in Utah to the disease as expressed

on sweet or sour cherry trees growing on mahaleb cherry rootstock.

The name "little cherry" has been commonly used in connection with

various diseases of cherries in which reduced size of fruit is a feature. It was

applied first to a disease of cherries occurring in the Kootenay Lake area of

British Columbia, Canada (73). It has also been commonly employed in

referring to a disease of cherries in Idaho, Oregon, Utah, and Washington (28,

29, 118, 185, 201, 254, 265). There are no data to establish whether there

is a relationship between western X-disease and the little cherry disease that

occurs in British Columbia (described on p. 126). In both Utah and Oregon

experiments have shown that the disease of the little cherry type affecting both

sweet and sour cherry and the western X-disease of peach and western chokecherry are caused by the same virus. In Utah Uttle cherry fruit symptoms

occur only on diseased cherry trees growing on mazzard rootstock, and the

names ''Utah httle cherry" and "western X little cherry" have both been apphed

to the disease. Experiments have likewise shown that a disease of the little

cherry type affecting Montmorency sour cherry and several varieties of sweet

cherry in Washington is an expression of infection with the western X-disease

virus. Interhost-transmission studies are still incomplete, but inoculum from

diseased sweet or sour cherry placed onto healthy peach resulted in the development of western X-disease symptoms, whereas similar inoculum placed onto

healthy sweet cherry resulted in the development of little cherry type symptoms. Tests on attempted transmission from diseased peach to healthy cherry

are incomplete.

In order to avoid confusion with the disease of sweet cherry called Httle

cherry in the Kootenay Lake area of British Columbia, the disease having

symptoms of the Httle cherry type on sweet and sour cherries associated with

western X-disease of peach in Idaho, Oregon, Utah, and Washington is referred

to in this section as "western X Httle cherry," a name previously used in Utah.

Name o£ the Causal Virus

"Western X-disease virus" is the common name proposed. No other name

is suggested for the virus, pending clarification of the possible relationship to

other viruses.

History

Blodgett (12, 13, 18) reported first observing the disease on peach in Idaho

891793°—51—Î

43
44 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

in 1936; and although transmission had not been demonstrated, he indicated

that the symptoms were typical of X-disease as it occurred in the East.

In 1955 and 193 6 Richards {192, pp. 3-4; 193, pp, U-^3) recorded

abnormal reddening of chokecherry leaves in northeastern Washington. Subsequently the disorder was identified as western X-disease. In 1937 Richards

recognized the same kind of red-leaf symptom on chokecherry in Utah.

In 1941 Richards and Hutchins {197) reported artificial transmission of

the disease from peach to peach as a result of graft inoculations performed in

1939 and 1940 in Utah and indicated that symptoms resembled in some, but

not in all, respects the X-disease described first in Connecticut {221).

Zeller and Evans {25^) reported transmission of the disease from peach to

peach in 1941, although the)^ had first recognized the disease in eastern Oregon

in 1939.

Bodine and Durrell {37) and Bodine {34) reported finding the disease in

Colorado in 1940 and transmission from peach to peach in 1941.

In 1940 Reeves and Hutchins (Í^7) published observations made in peach

orchards in Washington and other Western States. They attempted to distinguish the true symptoms of western X-disease from false symptoms

attributable to disorders of known, suspected, or unknown causes. Six groups

were listed; groups 1 and 2 were designations for the disease now known as

western X-disease, and a similarity of expressed symptoms to those of X-disease

in the East {221) and buckskin {HO), or leaf-casting yellows {234), in California was indicated; group 3 designated an unidentified disease; and groups

4, 5, and 6 designated diseases apparently attributable to several understandable

causes, but with symptoms that could easily be confused with those of western

X-disease. In 1941 Zeller and Evans {25^) described marginal leaf spot of

peach as a symptomatic expression of a distinct virus or a strain of the X-disease

virus and indicated that it was doubtless the disease described under group 3 by

Reeves and Hutchins {1S7). Jones {96, pp. 32-33) contributed information

on marginal leaf spot, designating it as the most important peach disease in

Washington and indicating that it was the same as the group-3 disease described

by Reeves and Hutchins {187). In 1942 Lindner and Reeves {139) published

data showing that the group-3 disorder described by Reeves and Hutchins

{187) was not a transmissible disease, but was due to arsenic toxicity.

Rawlins and Thomas {180) recognized two types of buckskin of sweet

cherry, one in Green Valley and another in Napa Valley of California. When

either of these types was transmitted from cherry to peach, symptoms similar

to those of X-disease developed on peach. The peach disease was first referred

to as leaf-casting yellows {234). The possible relationship of western X-disease

to buckskin has been indicated {187, 258) and is further discussed under

Remarks.

Wilt and decline of sweet and sour cherries on mahaleb rootstock described

for Utah {196) in 1945 was shown during 1941 to 1946 to be a virus disease

induced by the virus responsible for western X-disease on peach and western

chokecherry.

Western X little cherry occurring on either sweet or sour cherry on mazzard

rootstock in Utah was attributed to the western X-disease virus {198, 201),

The term "little cherry" was employed because of the failure of the fruit to

reach normal size and maturity rather than because of any known relationship

to the originally described little cherry {73) in British Columbia. The name

"little cherry" was also applied to the disease in Washington {28, 29, 185^
VIRUS DISEASES OF STONE FRUITS 45

254), Idaho (118), and Oregon (263, 265) without reference to the rootstock

on which the trees were growing. In Oregon Zeiler and Milbrath (265)

indicated the possible relationship of western X-disease of Montmorency cherry

which bore small, late-ripening fruits to buckskin of sweet cherry in California

(180).

On the basis of records for 10 years Lott found that in British Columbia

some peach trees became diseased and later showed weakness without leaf

symptoms, while a few affected trees returned to an apparently normal condition. On some trees leaf symptoms reappeared after having failed to appear

for a year or two. Lott (142) described small bitter cherry, a disease of sweet

cherry occurring in orchards adjacent to western-X-diseased peach in British

Columbia, but no definite transmission information has yet been obtained to

connect small bitter cherry and western X-disease.

Zeller (256) indicated that western X-disease of peach in Oregon probably

consisted of at least two forms. In Washington Reeves collected western

X-disease virus from a number of peach trees in different districts and found

considerable variation in the effects of the disease produced on comparable

experimentally infected peach trees; this variation suggested the probability

of different forms of the virus. Some of these forms may be closely related to

or the same as the virus causing other described diseases of the western X-disease group. It is recognized that further investigations are necessary to clarify

satisfactorily the relationship of western X-disease to other named virus diseases

of stone fruits, particularly pink fruit of sour cherry in western Washington,

Httle cherry in British Columbia, albino in southern Oregon, small bitter cherry

in the Okanagan Valley of British Columbia, buckskin in California, and Xdisease in the East.

Geographic Distribution

Western X-disease as referred to in this section has been reported in British

Columbia, Washington, Oregon, Idaho, Utah, and Colorado (34; 37; 96, pp.

29-31; 119; 154; 184; 194; 197; 258; 260). Similarity of the symptoms

described for buckskin to those of western X-disease on both peach and cherry

(180, 234, 265, 265a) indicates that California should be included.

In British Columbia the disease is limited to the southern part of the

Okanagan Valley; in Oregon and Washington it occurs east of the Cascade

Mountains except on the affected cherry trees reported in one location near

Mount Vernon, Wash. (254). The disease is more widely distributed on

western cholcecherry than it is on peach and cherries, because the natural

range of this plant is wider than the planting ranges of peach and cherries.

On peach, cherries, and chokecherry the disease occurs in both northern and

southern Idaho; in Utah it occurs in the great Salt Lake Basin; and in Colorado

it occurs principally in Grand County.

Economic Importance

Western X-disease is considered to be the most serious virus disease of

peaches in British Columbia, Washington, Oregon, Idaho, and Utah.

A survey of Washington peach orchards, conducted in 1942 and reported

by Coe (66), showed that 60 percent of the orchards inspected had western-Xdisease-affected trees and that on an average 2.4 percent of the trees in those

orchards were diseased.

In the Okanagan Valley of British Columbia individual-tree records showed

that 2.7 percent of 2,456 peach trees were diseased in 1940. By 1949 an

additional 6.9 percent of the trees originally surveyed had shown disease. In
46 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

1945 a survey showed that 1.5 percent of 3 5,469 peach trees were diseased and

that in orchards adjacent to wild hillsides up to 12 percent were aííected.

Western X-disease is a serious disease of peach in Baker, Malheur, Wasco, and

Umatilla Counties of eastern Oregon and is particularly serious on sweet and

sour cherries in Wasco County. Recent surveys showed that 2 5 percent infection in sweet and sour cherry orchards is not uncommon and several orchards

have nearly every tree affected. The number of infected cherry trees is

increasing at an alarming rate, and infection in many orchards is doubling each

year,

A survey of Washington cherry orchards made in 1947 (29) showed 1,491

diseased trees located on 295 properties. In a similar survey made in 1948

{254) 1,93 3 diseased trees were found on 344 properties. The percentage of

infection was reported highest in Asotin County and in the suburban districts

of Wenatchee and Yakima {254).

In 1943, 90 percent of the peach orchards in Davis, Box Elder, and Weber

Counties, of Utah, were found to have diseased trees and some orchards had up

to 83 percent of the trees affected {191). Observations in these same counties

during 1947 and later (200a) showed that sweet and sour cherries on mahaleb

rootstock had a high incidence of disease, that many trees were dead, and that

others were economically unprofitable and showed characteristic wilt and decline

symptoms. Sweet and sour cherries on mazzard rootstock also were severely

affected. A few older orchards of cherries on mazzard rootstock had up to 100

percent of the trees affected and, although they were seldom killed by the

disease, the trees were generally unproductive, the vegetative growth was

reduced, and the life of the tree was apparently shortened. The greatest

incidence of diseased cherry trees in Utah coincided with the occurrence of

the disease on both peach {190) and chokecherry.

In Idaho western X-disease is serious on peaches in all the principal peachgrowing districts and several peach orchards have been removed because of the

disease. The disease occurs on cherries in all of the principal cherry-growing

districts, but generally the percentage of infection is low, and many orchards

are not añ'ected. In a few orchards the disease has affected up to 50 percent of

the cherry trees.

Host Range

Western X-disease occurs on peach {Prumis pérsica), all varieties commonly

grown in the Northwest and other varieties and seedlings tested; nectarine

(P. pérsica var. nectarina); sweet cherry (P. aviuvi), all varieties commonly

grown in the Northwest and other varieties and seedlings tested; sour cherry

(P. cerasus) varieties Montmorency, Early Richmond, and Enghsh Morello;

and western chokecherry (P. virginiana var, demissa). In Utah the virus has

been transmitted by grafting to the eastern chokecherry (P. virginiana), Bessey

cherry (P. besseyi), and Manchu cherry (P. tomentosa).

Simonds {204) reported successful transmission to the Jones and Early

Home varieties of apricot (P. armeniaca) and to Big Mack (probably P.

imititia) and Duarte-Satsuma hybrid (probably P. mtinsoiüana X P- saUcina)

plums. Reeves and Hutchins {1^^) and Reeves {U4) reported negative

results in attempted transmission to Moorpark apricot and Itahan Prune (P.

dovtestica). In Utah ^^ apricot growing on peach rootstock was inoculated

with buds from diseased sweet cherry trees. No apparent symptoms developed

^' Wadley, B. N. Unpublished data.
VIRUS DISEASES OF STONE FRUITS 47

on the apricot, but western X-disease symptoms appeared on shoots growing

from the peach rootstock.

Symptoms

Peach.—Specific leaf symptoms generally become apparent on affected trees

from early June through July, depending somewhat on the season. In Washington Reeves found what appeared to be different forms of western X-disease

virus on peach. Trees infected with the severe form exhibited foliage symptoms

2 to 3 weeks earlier than those infected with milder forms. Also trees infected

with the severe form were often killed the second or third year after infection,

whereas those infected with a milder form were seldom killed, but showed a

slow decline over a period of years. Peach trees do not become uniformly

affected during the first year, but some twigs or branches exhibit symptoms

while others appear normal. Plate 7, C, shows a typical example of a Salwey

peach tree with some branches severely affected and others healthy. The initial

expression of the disease during the first year may be evident in only a single

branch or shoot. Affected twigs or entire branches frequently die during the

winter; such dying, together with growth during subsequent years, gives the

tree a one-sided and scraggly appearance.

In plate 8, B, is shown an Elberta peach tree in an advanced stage of the

disease. This is representative of a second- or third-year period of infection by

a severe form of western X-disease virus or of uve or more years after infection

by a milder form.

In general, the initial symptoms in early summer and those occurring on

leaves on rapidly growing shoots throughout the season consist of irregular

pale-green areas of varying size and shape in the lamina of the leaves. These

areas may involve large portions of the leaf blade, which may separate from

the normal leaf tissue and fall out, producing a shot-hole or tattered condition

of the affected leaves ( pi. 7, A). Leaves so affected remain pale green and

seldom develop the red and yellow colors characteristic of the disease later in

the season. Affected leaves become detached readily, and early defohation may

result.

On the leaves developing symptoms later in the season, water-soaked areas

appear in the lamina; these areas develop into necrotic spots of various sizes

and shapes. These necrotic areas may or may not drop out. The necrotic

tissue takes on a tan or dark-brown color, sometimes surrounded by a purphsh

border (pi. 9, top), especially in some varieties having a red fruit color. The

remaining portion of the affected leaf blade turns a greenish-yellow color and

has irregular spots, streaks, or splashes of red. In late season the reddish color

frequently follows the veins. Leaf fall is far less than during the earher

expression of the disease, and retention of affected leaves gives the tree a

characteristic yellowish to yellow-red appearance.

The margins of the leaves of most varieties often roll upward, but on

Lovell seedhng peach the leaves sometimes remain flat and clear yellow with

little mottling or necrosis. The amount of defoliation varies; defoliation may

be complete or nearly so on individual twigs and seriously affected branches.

During the late growing season other branches not so severely affected may

retain considerable foliage, but this foliage becomes prematurely yellow in the

fall. In plate 7, B, a branch of Orange Cling peach with some leaves having

already dropped, but with considerable yellow and orange-yellow foliage

remaining, is shown.

Fruits on severely affected branches usually shrivel and drop shortly after
48 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

the appearance of the first leaf symptoms. Fruits usually remain attached on

less severely affected branches and on branches which do not develop symptoms

until late in the season. Fruits on the less severely affected branches fail to

attain full size, ripen early, and sometimes fall from the tree 10 days to 2

weeks prior to the time of normal harvest. Such fruits are undersized and

somewhat conical in shape, have withered apexes (pi. 8, A), and are insipid

and bitter in flavor. Seeds of affected fruits fail to develop, and pits are

discolored.

Western chokecberry,—Symptoms on western chokecherry develop in late

June and July and show first as a greenish-yellow coloration. Later in the

season the leaves acquire a bright-red coloration. During the second year of

infection the leaves have a duller color, being mostly yellow with a little red.

Growth is stunted, and the leaves are smaller (pi. 8, D). Fruits, when they

occur, are smaller and more pointed than normal and in general exhibit the

little cherry type of symptom found on affected sweet and sour cherries (pL

8, C). Affected chokecherries may die out rather rapidly in some districts or

may persist in a declining condition for many years.

Sweet and sour cherries on mahaleb rootstock. ^^—In Utah western-Xdisease-afífected sweet and sour cherry trees growing on mahaleb rootstock may

wilt at any time during the growing season. The disease may be detected as

early as late April or early May by the light-green or yellow leaf color and by

the flaccid appearance of the leaves (pi. 10, C, D). Wilting may be so rapid

that, as shown by the middle tree of plate 10, D, the leaves die without forming

an abscission layer, become reddish brown, and persist on the tree throughout

the summer and following winter.

Frequently, affected trees wilt slowly and retain their leaves until later in the

season. Such trees may continue to live in a weakened, or declined, condition

for several years. Leaves on slowly declining trees are retarded in development,

smaller in size, more linear in shape, lighter green in color, and more sparsely

distributed on the tree than normal. Defoliation occurs much earlier in the

fall on affected trees than on normal ones of the same variety.

Diseased trees in the early stage of decline have a tendency toward delayed

but excessive blooming and a heavy fruit set (pi. 11, £). Such declining trees

may wilt abruptly and die after this excessive fruit setting. Fruits color earlier

than normal, but they seldom develop full normal color or size and appear to be

more elongated. Roots of severely diseased trees are always damaged. Usually

the small rootlets and the cortex of the root are dead or decayed by late fall and

the xylem is darker in color than that of healthy roots. Affected roots die

progressively from the tips to the trunk.

Sweet and sour cherries on mazzard rootstock.—In Utah the symptoms on

sweet or sour cherry on mazzard rootstock affected with western X-disease are

most evident on the fruits although the foliage and the growth of the trees

are also affected. Affected fruits are seldom more than half normal size and are

inclined to be more pointed than normal and retain the pinkish-red or yellowishgreen color of immature fruits far beyond the normal picking date (pi, 11, A).

Affected fruits often exhibit a dull luster rather than a normal glossy appearance. They also definitely lack the flavor and sweetness of normal cherries.

Affected fruits remain attached to the tree long after normal fruits are

harvested, but they never acquire normal color.

The information given on sweet and sour cherries on mahaleb rootstock is limited to

observations in Utah.
VIRUS DISEASES OF STONE FRUITS 49

In Utah (201) symptoms in addition to reduced size of fruits are often

associated with the disease, particularly on sweet cherry. Stipules may become

elongated and broadened and persist much longer than on healthy trees; bud

scales may remain attached several weeks after the buds open in the spring; and

internodes on new growth may become shortened and thus give the trees a

rosetted appearance. Leaves may be somewhat smaller and paler green than

healthy leaves of the same variety. A few terminal buds break dormancy in

late fall, and thus secondary growth results.

In Washington (29) symptoms in addition to those exhibited by the fruits

are recognized as associated with western X-disease even though positive

diagnosis of affected trees depends upon fruit symptoms. These additional

symptoms become apparent after harvest. They have been found on severely

affected trees and are absent or nearly so on lightly affected trees. The most

noticeable of these symptoms is a fading of the dark-green color of some

leaves to a yellowish green, which later becomes light brown to bronze. The

coloration of the foliage is variable; a few leaves may appear severely sunburned, others are light brown, and about half of the foliage appears nearly

normal or dull green. The bronzing of the foliage on severely affected trees

readily distinguishes them from trees with normal-appearing foliage. Other

symptoms that have been observed are separation of the bud scales (particularly

on spurs previously bearing small fruits), which results in such buds having a

frayed appearance, late blossoming, and a variable percentage of the terminal

buds breaking into secondary growth. In Washington an occasional stipule

may be found slightly elongated and broadened but the shape change is much

less pronounced than in Utah. Also in Washington affected trees are not found

with a pronounced rosetted appearance as they are in Utah.

In plate 9, bottovt, western-X-little-cherry-affected fruits from an affected

Bing tree in Washington are shown in comparison with normal fruits taken

from the same tree. The relative percentage of small fruits on affected treec

varies with variety even when the entire tree is generally affected. Severely

affected Lambert and Black Republican trees have been observed with no fruits

of normal size, but it is not unusual to find a severely affected Bing tree with 20

to 3 0 percent of the fruits apparently normal or nearly so. In plate 11, ß and

C, western-X-little-cherry-affected fruits from affected Napoleon (Royal

Ann) and Lambert trees in Washington are shown in comparison with normal

fruits taken from the same trees. Fruits from a severely affected Lambert tree

are often conical or triangular in shape.

The first year a sweet or sour cherry tree exhibits symptoms of the disease,

it is not unusual to find the small cherries confined to one or two branches. In

other instances, especially on small trees, nearly every fruit is affected the first

year that symptoms appear.

In Oregon the symptoms on sweet cherry are much the same as described in

Washington. There are no reliable foliage symptoms and no appreciable decline

in sweet cherry trees for several years after infection. On the Montmorency

variety of sour cherry there is a rapid decline followed by dieback, a typical

example of which is shown in plate 11, D. An infected tree produces no

marketable fruit the second or third year after infection. The right side of

the tree shown has seriously declined and many small limbs are dead, while

relatively good foliage remains on its left side. In plate 10, B, fruits from an

affected Montmorency tree in Oregon are shown in comparison with normal

fruits from the same tree.
50 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Transmission

Transmission has been reported by grafting or some adaptation of the

grafting process and by the geminate leafhopper {Colladomis geminatus

(VanD.)) {2na),

On peach there is considerable variation in the percentage of positive infections in graft-transmission experiments, depending upon the season of inoculation, the type of inoculum employed, the length of time the inoculum has

been held after removal from a diseased tree before transmission is attempted,

and probably the vigor of the tree being inoculated. The percentage of positive

infections obtained is relatively high with inoculum taken early in the

season as soon as recognizable symptoms appear and relatively lov7 or zero in

late summer, early fall, and the dormant season.

In early work in Oregon, after an incubation period of 2 years, only 4 cases

of western X-disease resulted from Zeller's inoculation of 32 peach seedlings

with inoculum from naturally infected western chokecherry. Later Zeller and

Milbrath {265) made successful interhost transmissions of several diseases

occurring in Wasco County, Oreg., by grafting and decided that western Xdisease of peach, red-leaf of western chokecherry, and "Kttle cherry" of sour

and sweet cherry occurring there are all caused by the same virus. They also

found that peach trees conditioned by prior infection with latent viruses

commonly occurring in cherry trees gave a higher percentage of western Xdisease upon receiving inoculum from western-X-disease-aifected sweet or sour

cherry trees.

In Utah {196, 199) western X-disease virus from western chokecherry has

been repeatedly inoculated into nursery trees of sweet and sour cherries growing

on mahaleb rootstock and wilt and decline has resulted. Wilt and decline has

likewise been induced on English Morello cherry by western X-disease virus

taken directly from peach and indirectly on sweet and sour cherries from the

peach after passage through western chokecherry.

By inoculation with buds and fruit spurs from diseased sweet and sour cherry

trees in Utah (Í98, 201), typical western X-disease symptoms were produced

on peach, typical red-leaf and characteristic small fruits on eastern and western

chokecherries, and wilt and decline on sweet and sour cherries growing on

mahaleb rootstock. The wilt and decline produced appeared identical with

that induced by the western X-disease virus from western chokecherry and

with that occurring in orchards.

In Utah when normal sweet or sour cherry is top-worked on individual

branches of a mahaleb tree and some of the resulting-variety branches are

separately inoculated with western X-disease virus, the branches thus infected

develop wilt and decline but the uninoculated branches remain normal. In

plate 10, A, is shown a tree of mahaleb understock with three arms which had

normal Bing buds inserted near a point indicated by the white tag just above

the crotch on the branch at the right. The two outside branches, subsequently

inoculated with buds taken from diseased western chokecherry show characteristic wilt and decline. The center branch, which was not inoculated,

remained normal.

Incubation Period

Peach trees inoculated with western X-disease virus in late summer by

budding exhibited symptoms the following year at the usual time when

symptoms of the disease appear. In 1941 Richards and Hutchins {197)

reported as follows: "Of 40 Elberta nursery trees inoculated on July 26, 1940,
VIRUS DISEASES OF STONE FRUITS 51

all trees developed the disease within 6 weeks." Peach trees inoculated in late

May by Reeves developed symptoms within 50 days.

In Utah, sweet and sour cherry trees grown on mahaleb rootstock inoculated

in late summer usually showed wilt symptoms the following season from May

to early September. Cherry trees on mahaleb rootstock inoculated by Richards

in early June developed symptoms in 3 ^ months.

In Washington Blodgett and Reeves obtained symptoms on sweet cherry on

mahaleb rootstock in late June 1949 from inoculations made March 25, 1949,

during the late dormant season. Reeves and Blodgett obtained symptoms on

sweet cherry on mazzard rootstock during mid-June from inoculations made

in mid-September of the previous year.

Control Measures

In the Western States western X-disease spreads from peach to peach. The

suggested method of control on peach is destruction of infected trees in order

to keep the disease at a minimum.

Practical measures suggested for control of the disease in cherry vary in

different districts. In some districts in Utah the disease on cherries is in such

high concentration that it is doubtful that a roguing program would be

effective. In certain districts in Washington having a very low concentration

of the disease roguing programs were employed from 1947 through 1949 with

apparently good results. Top-working desirable cherry varieties on mahaleb

framework is being attempted in Utah, but the results are not yet apparent.

Work on chemotherapy is in progress, but no practical results have been

obtained so far.

Preventive measures such as the careful selection of nonaffected propagation

wood for both peaches and cherries is especially recommended. Roguing

programs are also suggested, particularly in districts where the disease on either

peach or cherry is in low concentration.

Remarks

Although the exact relationship of western X-disease to X-disease as described

in the East {100, 172, 226) has not been established, there is considerable

similarity in their symptoms as expressed on peach, chokecherry, and cherries.

Unpublished observations by some of the authors of this section indicate that

possible greater differences occur in the symptom expression of western Xdisease on peach in various localities in the Western States than usually occur

between symptoms of western X-disease and X-disease on this host. One

of the principal differences is apparently the manner of field spread. In the

East natural spread of X-disease is reported to be mostly from chokecherry to

peach (100, 221) while in the West chokecherry is apparently not necessarily

an important factor in the field spread of western X-disease. This difference

might be explained more plausibly as a vector relationship rather than as

differences in the viruses, as judged by the expression of symptoms on peach.

The similarity of symptoms of buckskin or leaf-casting yellows of peach in

California to western X-disease and X-disease in the East has been indicated

(2 50, 1S7, 234). Zeller and Milbrath (265) also indicated a relationship of

western X-disease occurring on several hosts in Wasco County, Oreg., to

California buckskin in the following statements:

The disease transmitted to sweet cherry causes buckskin disease and transmitted to peach trees

causes Western X-disease. A table of 54 cross transmissions of Western X-disease of peach,

red-leaf chokecherry disease, and the "little cherry" found in Montmorency cherry and

several sweet cherry varieties in Wasco county, Oregon, indicates that all of these diseases are
52 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

caused by the same virus, or that the infected trees contain the Western X-disease virus. The

symptoms of this disease of sweet cherry look the same as those of the buckskin disease of

sweet cherry in Green Valley, California. On the other hand, the disease in Oregon has not

been demonstrated to react to Mazzard and Mahaleb rootstocks as reported by Rawlins and

Parker for the buckskin disease of cherry in California.

Symptoms of buckskin on cherry top-worked on mahaleb understock as

reported in California (ISO) are similar to the wilt and decline symptoms of

western X-disease reported in Utah (198), The data available at present and

personal observation by several of the authors of this section indicate that there

is considerable similarity of western X-disease in the Northwest, X-disease

in the East, and buckskin in California. It is recognized that there are

different forms of western X-disease probably, just as two forms of buckskin

have been reported in California (180).

The general policy of not moving virus material to districts where the

disease is not known to occur has not permitted direct comparison under the

same growing conditions. The authors acknowledge similarities and probable

relationships but feel that grouping should await more data.
Agriculture Handbook 10, U. S. Department of Agriculture PLATE 1

A, Normal immature peach fruits; B, comparable fruits affected with peach yellows, showing early maturity; C,

trunk of peach-yellows-affected peach tree, showing wiry shoots with small leaves; D, portion of little-pcachaffected peach tree, showing clustered, drooping leaves; £, immature fruits from Elbcrta peach tree affected

with little peach; F, comparable normal mature fruits.
Agriculture Handbook 10. U. S. Department of Agriculture PLATE 2

A, Elberta peach foliage affected with peach rosette, in contrast with normal at left. B-D, Comparable peach

shoots: B. From normal tree, with slightly immature fruits; C, from little-peach-affected tree, showing drooping

foliage and immature fruits; D, from red-suture-affected tree, showing fruits colored on the suture side. E,

Peach fruits showing enlarged, reddened suture side characteristic of red suture.
Agriculture Handbook 10. U. S. Department of Agriculture PLATE 3

Af Normal Hilcy peach, ß, Comparable fruit from phony-aíTcctL-d truL-. C and D, Transverse serial sections of

root from phony-affected peach tree: C, Before chemical identification test; D, after test, showing color reaction

in the woody cylinder. £, Three-year-old J. H. Hale peach tree affected with rosette mosaic, with a normal

shoot in the center.
Agriculture Handbook 10, U. S. Department of Agriculture PLATE 4

Peach mosaic: A, Florence peach flower showing broken color pattern; B and C, J. H. Hale peach (B) affected fruits,

showing reduced size, bumpy surface, and uneven color as compared with normal at lower right, and CO leaves

showing a gradient of mosaic mottling (veinlet clearing, right; brilliant mottle, center; and marginal striping,

left); D, partially affected J. H. Hale peach tree, showing retardation on affected side.
Agriculture Handbook 10, U. S. Départaient o( Agricultvie PUATE 5

Peach tree naturally affected with X-disease, showing abnormal coloration, leaf rolling, and defoliation of affected

branches as contrasted with unaffected branches.
Agriculture Handbook 10. U. S. Department of Agriculture PLATE 6

A and B, Montmorency sour cherries: A, Normal; B, affected with X-disease. C and D, Windsor sweet cherries: C,

Affected with X-disease; D, normal. E, Chokecherry affected with X-disease, showing brilliant foliage

coloration the first season after infection.
Agriculture Handbook 10, U. S. Department of Agriculture PLATE 7

Western X-disease on peach: A, Elberta leaves showing early-season symptoms; B, Orange Cling branch showing

late-season symptoms; C, Salwey tree showing affected shoots interspersed with normal ones.
Western X-disease; A, Comparable normal and affected Elberra peach fruits; S, severely affected Elberta peach tree having only one unaffected branch; C, comparable normal

and affected western chokecherry fruits; D, normal and affected chokecherries showing second-year symptoms.
Agriculture Handbook 10. U. S. Department of Agriculture PLATE 9

Top: Elberta peach leaves affected with western X-disease, showing greenish-yellow color and

irregularly shaped reddish spots, necrotic areas, and holes in contrast with normal leaf.

Bottom: Normal and western-X-little-cherry-affected Bing cherry fruits.
tti^S

A, Bing cherry top-worked separately on arms of mahaleb cherry understock 2 inches above the crotch; outer branches subsequently inoculated with western X-diseasc virus.

B, Normal and westcrn-X-little-cherry-affected Montmorency cherry fruits. C, Thirty-year-old Bing tree on mahaleb rootstock naturally affected with western "D

X-disease wilt (right and left). D, Young Napoleon cherry trees on mahaleb rootstock inoculated with western X little cherry virus, showing collapse. ^
Agriculture Handbook 10. U. S. Department of Agriculture PLATE 11

..^^^'.

f

-5¿

^, Normal and western-X-little-cherry-afFected Napoleon cherry fruits, Utah; B, similar fruits, Washington;

C, similar Lambert cherry fruits, Washington; D, Montmorency cherry tree severely affected with western

X little cherry ; £, 5-year-old Bing cherry tree affected with western X little cherry, showing excessive fruiting.
Agriculture Handbook 10, U. S. Department of Agriculture PLATE 12

^^^^^^pn^^^^^^*

1

m §5

1i

1!

A, Peach fruits affected with wart

proliferation of leaves; C, compara

bv peach mottle.

B, shoots of Bing cherry affected with peach mottle, showing mottling

irable normal shoot; D, peach leaves showing mottling and puckering ca

and

puckering caused
Agriculture Handbook 10, U. S. Department of Agriculture PLATE 13

A, Rio Oso Gem peach tree affected with ring spot, showing acute symptoms (retarded foliation, bud killing, and

dieback). B, Same tree approximately 1 year later, showing recovery. C-E, J. H. Hale peach affected with

ring spot: C, Early-spring leaves arranged to show a gradient of symptoms; D, trunk of young tree showing

bark splitting below inoculation point; E, inoculated tree showing shock and dieback in contrast with healthy

tree (Ich^. F, Three Fay Elberta peach trees pruned to same height the previous winter, showing reduced

vigor of two trees chronically infected with ring spot as compared with normal tree (left).
Agriculture Handbook iO, U. S. Department of Agriculture PLATE 14

A and B, Cherries from buckskin-affected trees: A, Napoleon; ß, Bing. C and D, Comparable normal fruits.

E-G, Leaves from plants affected with buckskin: E, Western chokecherry, showing carmine color; F, peach,

showing rolled edges and purple and necrotic spots; G, sweet cherry on mazzard rootstock, showing latesummer and fall symptom, orange to red color along the basal portion of the midrib.
YELLOW BUD MOSAIC

By H. EARL THOMAS and T. E. RAWLINS

Other Common Names of the Disease

Winters peach mosaic.

Name of the Causal Virus

Inops consilH Thomas, Scott, Wilson, and Freitag {2} 5),

Geographic Distribution

Yellow bud mosaic has been found in about 50 orchards in Solano and Yolo

Counties, Calif.

Economic Importance

Trees of Elberta, Lovell, and Muir peach, the common varieties in the

affected district, are reduced in a few years to an unprofitable state; and small

trees may be killed in a few months. Almond is injured to an intermediate

degree, but it becomes infected infrequently. Apricot is readily infected, but

it is damaged little.

Host Range and Varietal Susceptibility

Natural infection is known on almond (Pmntis amygdahs), apricot (P.

armeniaca), and peach (P. pérsica) (23 3). Old apricot trees apparently

may be symptomless carriers. The peach varieties Babcock, Elberta, Fay

Elberta, Florence, Lovell, J. H. Hale, Peak, and Rio Oso Gem are about equally

affected when artificially inoculated. Foster is somewhat less susceptible.

Under natural conditions Elberta, Lovell, and Muir varieties are seriously

injured. The causal virus has been transmitted by grafting to the following

species: Almond, apricot, Portuguese iaurelcherry (P. Imitanica), Japanese

apricot (P. mtime), rose {Rosa sp.) variety Ragged Robin, Japanese kerria

{Kenia japónica), desert peach (P. andersonii) on peach roots, sweet cherry

(P. avium), and myrobalan plum (P. cerasifera)—the last by passage from

peach through desert almond (P. fasciculata),

Symptoms

Peach.—At the onset of disease, pale-green to pale-yellow, oblong, featheredged blotches develop along the midvein or larger lateral veins of peach

leaves, with distortion of the leaf blade and frequent dropping out of the

chlorotic areas (fig. 16, A). Leaves which are relatively mature at the time of

invasion may develop only small chlorotic flecks about 1 mm. in diameter. In

advanced stages of the disease the leaves are shed until the basal portions of

affected branches may be bare or nearly so {ñg, 17). Elsewhere the buds often

push out until they are a few milHmeters in length and remain practically at a

standstill for several weeks {ñg. 16, ß). They are pale yellow. Later such

buds die or slowly produce rosettes of small, often distorted leaves with or

without mottUng. Some dwarfing and malformation may occur on fruits of

Muir peach but not on those of Elberta or Lovell. No flower symptoms are

known.

Almond.—In the spring the leaves are mottled {üg. 16, C) and the foUage

is sparse. Later there are terminal tufts of leaves with Uttle or no mottfing.

Apricot.—On the leaves there are occasional circular spots, usually about

891793°—n—6

53
HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

figure 16.—A and B, Leaves (A) and twig with arrested buds (B) of a peach seedling affected with yellow bud mosaic; C, leaves of Texas almond naturally affected

with yellow bud mosaic, early in season.
VIRUS DISEASES OF STONE FRUITS 55

figure 17.—Orchard Lovell peach tree in advanced stage of infection with yellow

bud mosaic.

10 mm. across, with necrotic centers and chlorotic halos. Old trees show no

symptoms, though there is evidence that they supply the virus to peach.

Transmission

The disease can be transmitted by grafting. In orchards spread occurs

typically from infected trees to adjacent trees only (23 5).

Incubation Period

The incubation period varies from 3 weeks to several months, depending on

the growth condition of the tree at the time of inoculation and perhaps on its

size.

Control Measures

A quarantine has been placed on the affected district to reduce the movement

of infected budwood to other districts. Eradication is being attempted in

some orchards, but results thus far are not conclusive. Almond and apricot

grow satisfactorily in place of peach but allow the building up of a reservoir

of infected material. Pear and plum would be even more sure of success in

those parts of the district adapted to them.
WART

By EARLE C. BLODGETT, J. A. MILBRATH, E. L. REEVES, and S. M. ZELLER

Names of the Disease

The disease is most commonly called wart. It was referred to as blister,

however, in the first report of its occurrence (13, sec. 3).

Names of the Causal Virus

The causal virus was named ^^Galla verrucae Blodgett" (21). Under the

system of naming proposed by Fawcett the name would be ^^Prunivir verruca.''

Geographic Distribution

Wart has been reported as occurring naturally in Adams, Washington, Gem,

and Canyon Counties, Idaho (21); in Yamhill (262) and Malheur Counties,

Oreg.; in Chelan, Douglas, Klickitat, and Yakima Counties, Wash. (184);

and in San Bernardino and Riverside Counties, Calif. (228). Infected fruits

were observed in 1948 in an orchard in Twin Falls County, Idaho. Artificially

infected trees occur in Latah County, Idaho (21),

Economic Importance

Generally the number of affected trees is small; but, because of the danger

of spread through nursery stock and of possible orchard spread, wart is a

serious, potential menace to peach orchards. In 1945 an orchard survey of 300

trees of 1 variety, top-worked in 1941, showed that more than 200 of them

bore warty fruits. In this instance all trees of the affected variety were

removed {228). Since most diseased trees show a high percentage of warty

fruits, they are considered useless and also they are hazardous to fruit growing

because they are a source of inoculum.

Host Range

Wart is known to occur naturally on seedlings and the Elberta, J. H. Hale,

Early Crawford, Candoka, and Halberta varieties of peach (Prtmus pérsica)

(21). It was transmitted by bud inoculation also to Early Crawford, Early

Muir, Improved Elberta, Rio Oso Gem, Orange Cling, and Rochester (262).

No natural infection is known on sweet cherry (P. avm7n), but Black

Republican, Napoleon (Royal Ann), and Lambert varieties were artificially

infected by bud inoculation (262). Buds from wart-diseased peach trees

grafted on young Italian Prune (P. domestica) trees produced shoots that

bore warty fruit for three seasons, but no symptoms were observed on the

leaves or fruits of the prune. Tests have not been completed to determine

whether the prune wood carries the virus.

Symptoms

Peach.—The first symptoms appear on the very young fruits, shortly after

the calyxes have fallen, as bleached bumps or raised welts on or near the

stylar end and often involving half or more of the fruit (21, 184). The fruits

are both dwarfed and misshapen if the disease is severe, but slightly afiected

fruits are nearly normal in size (pi. 12, A). The surface of affected tissue

varies in color from light tan to conspicuous red and may be rough with wart^

outgrowths conspicuously raised, or it may be rather smooth or cracked and

russeted (ñg, 18). Gum is usually present and may be extremely abundant.
VIRUS DISEASES OF STONE FRUITS 57

Figure IS.—Peach fruits with wart: A, Rough type; B, smooth type.

The warty tissue is rather superficial, but the underlying tissue is coarse and

filled with gum pockets. In some cases the warty tissue is very hard and

bonelike, but usually it is tough and leathery. Frequently warty tissue occurs

in ringlike patterns near the stylar end.

In the study of peach wart, certain variations were found and described by

such names as "smooth wart," "crease wart," and "beady wart." In recent

tests by Blodgett it appeared that smooth wart is transmissible as such; that

crease wart is not caused by a virus, but is associated largely with certain

varieties (Rio Oso Gem in particular) ; and that beady wart is probably caused

by insects. There appeared to be no constant difference in expression of

symptoms by the different peach varieties.

In most wart-affected trees observed, there are no leaf symptoms visible. In

a few cases, however, there are variable amounts and degrees of mottling, which

is often mild and fleeting. This mottling is essentially indistinguishable from
58 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

that caused by the peach mottle virus (18, 21) and has been easily transmitted. Trees having both wart and mottling may, therefore, be infected by

virus mixtures.

In general, wart-aííected peach trees show no reduction in size, vigor, or

production.

Stveet cherry.—^hck Republican, Lambert, and Napoleon varieties of sweet

cherry showed stem and leaf symptoms when inoculated with peach buds

infected with peach wart virus {262). The symptoms described by Zeller and

Milbrath {262, p. 607) are as follows:

^ In the Napoleon variety the stem symptoms at first are limited to necrosis in the vascular

nng. This necrosis as far as 12 to 15 inches back from the tips results in a general dieback . Sometmies there is more than normal branching. In addition the internodes

of the last few inches near the terminals of the several branches are shorter and considerably

larger in diameter than normal. This condition and resulting "leanness" of the terminals

give a rosetted appearance. There is a tendency toward smaller, narrower leaves as a result

of crowding in the rosettes.

The mottling produced in the leaves of the Napoleon variety is more characteristic and

distinct than that produced in Black Republican or Lambert varieties of cherry. The

mottling seems to start with chlorosis bordering veinlets. This spreads out to form larger ringlike patterns or even somewhat rectangular bands or lines on either side of the veins. , . In May

and June the symptoms are especially prominent on most of the young leaves. As the season

progresses and the leaves mature the symptoms become less conspicuous, until finally in late

August the mottling has disappeared in all of the matured leaves, even though they may have

been mottled earlier.

There is a similarity between mottling produced in cherry leaves by peach-wart virus and

that produced by mild-mottle-leaf virus. Warty fruits, however, are not produced when peach

trees are inoculated with mild mottle leaf of cherry. Cherry trees with the mild-mottle-leaf

disease likewise do not have the stem symptoms described for peach wart in cherry.

Diagnostic or Unusual Characteristics

Peach wart virus produces spectacular symptoms on peach fruits, but affects

the trees very httlc. One of the diagnostic symptoms is the localization of wart

tissue near the stylar end of mildly affected peach fruits or its prevalence there

on severely affected fruits.

Transmission

Artificial infection by peach wart virus has been obtained principally by

budding or inarching. It has been shown that severity of wart symptoms in

one season after inoculation is related to the amount of inoculum used {21).

Zeller and Milbrath obtained severe infection in 4-year-old peach trees by the

insertion of three to uve diseased buds. Inoculations made by Blodgett in

1943 showed by 1945 that transmission of the virus was easily obtained by

grafting warty fruit tissue into young peach tree trunks {26). Wart was

transmitted by Zeller and Milbrath from peach to sweet cherry and back to

peach by bud inoculation (262).

Incubation Period

Diseased peach buds inserted September 7, 1940, produced warty fruits on

some peach trees by June 13, 1941, whereas in other cases evidence of transmission was not visible until the second season. Sweet cherry trees budinoculated in August began to show leaf and stem symptoms the next April

(262).

Control Measures

It is recommended that all diseased trees be removed promptly and that

budwood from wart-free trees be used for propagation.
PEACH MOTTLE

By EARLE C. BLODGETT

Other Common Names of the Disease

None.

Name of the Causal Virus

Peach mottle virus.

Geographic Distribution

Single naturally infected peach trees were found in Gem and Payette

Counties, Idaho, and several experimentally diseased trees are known in Latah

County. On the basis of symptoms on one tree seen by the author the disease

is considered to occur in Malheur County, Oreg. A mottle associated with

peach wart was seen in Canyon County, Idaho. (See 13y sec. 2; 17; 19;

20; 21.)

Economic Importance

Peach mottle is regarded as of minor importance at present.

Host Range

The disease has been seen in orchards only on Elberta peach {Prumcs pérsica).

In experimental-transmission tests mottle symptoms were produced on the

varieties J. H. Hale, Elberta, and Slappey and on peach seedlings; on sweet

cherry (P. avmm) varieties Bing, Napoleon (Royal Ann), Lambert, and

Black Republican and on mazzard (P. av'mm) seedlings; on sour cherry (P.

cerastes) variety Montmorency; and on May Duke (semisweet cherry). The

Moorpark apricot (P. armeniaca) is listed as a possible host of peach mottle,

but it has been inadequately tested. In several inoculation trials no definite

symptoms were produced on the Italian Prune variety of domestica plum (P.

domestica). No tests were made to determine whether this variety is a

symptomless carrier.

Symptoms

Peach.—The original affected Elberta tree presented a ragged appearance

and in general was lighter green than normal trees. Growth was reduced, but

rosetting was not characteristic. The fruits showed no consistent differences

from normal, and no breaking in the color pattern was observed on the

blossoms. The leaf symptoms consist of coarse mottling, slight dwarfing,

rolling of the margin, deformity, and puckering (ñg. 19, A; pi. 12, D).

Leaf symptoms on the different peach varieties are similar, but the amounts of

mottling vary markedly. Young trees bud-inoculated with peach mottle virus

grew poorly, and several died. Symptoms are pronounced early in the season;

later they become partially masked.

Cherry.—The first tests on transmission of peach mottle to Bing cherry

resulted in very marked symptoms, and at first peach mottle was thought to be

similar to cherry mottle leaf (1S3) (üg. 20, C, D). Later, however, much

more extensive dwarfing, mottling, and necrosis of foliage accompanied by

marked tree stunting, shoot necrosis, and dieback showed the disease to be

distinct from mottle leaf (pi. 12, B). Symptoms on the Napoleon variety are

similar to those on Bing except that the effect is generally much less severe.

Inoculated trees of the Lambert variety developed a chlorotic veinlet banding

59
60 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Figure 19.—A, Leaves from a J. H. Hale peach tree artificially infected with peach

mottle virus; B, twigs from a Montmorency cherry tree affected with peach mottle,

showing gum exuded from pockets in the bark.

appearing much like a golden-net pattern. Symptoms on the Black Republican

variety (fig. 20, A) are similar to those on Lambert, but they are much more

severe, giving the foliage a light-green color. This reaction, similar to that on

Lambert, distinguishes cherry mottle leaf from peach mottle. Symptoms of

mottling developed on inoculated mazzard seedling stock and on mazzard

shoots from roots on infected Bing trees.

On the Montmorency variety of sour cherry peach mottle produces mild to

severe mottling (fig. 20, B) and much twig dieback. Associated with this

dieback is an abundant formation and exudation of gum on both old and young

twigs (fig. 19, B). In some cases the gum pockets cause stem swellings,

cracks, or both in the bark. There is a tendency for trees to appear somewhat

rosetted.

Diseased trees of the May Duke variety are dwarfed, principally from the

necrosis and dieback of terminal shoots. Pronounced leaf mottling and vein

clearing also arc present.

Apricot.-—In one test with two Moorpark apricot trees, definite, although

mild, mottling of the foliage appeared the next season after bud inoculation.

No transmission test was made from these trees back to cherry or peach to

determine whether the symptoms on apricot were a result of the peach mottle

virus.
VIRUS DISEASES OF STONE FRUITS 61

figure 20.—A-C, Leaves from cherry trees artificially infected with peach mottle

virus: A, Black Republican; B, Montmorency; C, Bing. D, Comparable leaves from

Bing cherry tree affected with mottle leaf.
62 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Diagnostic or Unusual Characteristics

Peach mottle virus produces severe symptoms on Lambert, Black Republican,

and Montmorency cherries; therefore, it is distinguished from cherry mottle

leaf, which produces only mild symptoms on these hosts. In tests made by

Cochran ^^ in Texas with Idaho peach mottle material, the virus was determined

to be distinct from that causing peach mosaic although on peach both produce

mottle symptoms which are similar in some respects. Peach mottle is further

distinguished from peach mosaic by the production of symptoms on cherries,

which are immune from the peach mosaic virus.

Transmission

Repeated trials have shown that peach mottle is easily and consistently transmitted by means of buds from peach to peach and from peach to cherry (both

sweet and sour) and back to peach (IS).

Incubation Period

Peach or cherry trees bud-inoculated in the fall (September) usually show

symptoms of mottle when they leaf out the next spring.

Control Measures

Infected trees should be removed promptly, and budwood from healthy

trees should be used for propagation.

Remarks

In some peach trees affected with wart a motthng of the leaves similar to

that produced by peach mottle was noted. Transmission from such trees

resulted in both wart and mottle on peach and a reaction on cherry similar to

that caused by the peach mottle virus. Such cases undoubtedly represent

infection by at least two viruses.

' Cochran, L. C. Unpublished data.
MUIR PEACH DWARF

By LEE M. HUTCHINS, C. F. KINMAN, L. C. COCHRAN, and GILBERT L. STOUT ^^

Names of the Disease

'*Muir peach dwarf" is proposed as a good descriptive name of the disease

for reasons that appear under Symptoms. The term ''rosette" was employed in

the earhest mention of the disease by the late W. T. Home in 1920, and the

name "Muir rosette" has been used (213, p, 91)»

Name of the Causal Virus

Muir peach dwarf virus.

History and Geographic Distribution

The disease here called Muir peach dwarf came to Kinman's attention in an

old orchard of the Muir peach variety near Chico, Calif., in September 193 5.

Afiiected trees exhibited symptoms suggesting phony, and Hutchins, who had

worked extensively with that disease in Georgia, was requested to examine the

trees near Chico. This led to the investigational work that yielded the information presented here.

Upon approaching the affected Muir peach trees, the investigator noted the

very striking resemblance of the disorder to phony. Closer observations, however, disclosed points of difference. Also the chemical test for phony (pi. 3, D)

was clearly negative when made on roots of Muir trees showing advanced

stages of the disorder, and the latter was regarded as a new disease.

The information obtained during these examinations and photographs of

affected trees were brought to the attention of Max W. Gardner and Ralph E.

Smith, Department of Plant Pathology, University of California, Berkeley.

They recalled earlier mention of apparently the same disorder and referred to

records left in the Department by Home. With the kind permission of

Gardner, these first-known records of Muir peach dwarf are summarized here.

On April 3 0, 1920, Home observed on Muir peach trees at Suisun Valley,

Solano County, symptoms which he regarded as resembling peach rosette or

phony; the grower stated that the trees had been affected for several years.

Home further noted that Elberta peach trees interplanted with the Muir

trees in this orchard were not afifected. On October 28, 1920, he observed the

same disorder at Mountain View, Santa Clara County, where 2 or 3 acres of

Muir trees showed shortened twigs. Apparently the trouble had been present

for 10 or 12 years and had spread windward. Smith supplemented these

statements with the interesting comment that, in passing the orchard at Suisun

Valley about October 10, 193 5, he observed that the disease was still there.

With the discovery of extremely dwarfed Muir trees at Chico, about 150

miles north of Suisun Valley, the disease assumed new interest and it seemed

desirable to determine whether it was infectious. The results of inoculation

experiments performed by Hutchins and Kinman in 1936 and 1937 placed

Muir peach dwarf in the group of graft-transmissible virus diseases. Various

phases of the work were further developed by these investigators until July

' By mutual agreement associate authorship is not alphabetical.

63
64 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

1941. Since 1941 Cochran and Stout have continued with the research and

observations.''^^

Muir peach dwarf has been seen only in orchards of the Muir peach variety

and is known to occur in several counties of middle California. It has not

been reported elsewhere.

Economic Importance

Muir orchards Hghtly infected or free of the disease may adjoin or be near

heavily infected orchards. Spread tends to be local, slow, and mostly in closecolony formation. Mature fruits on diseased trees are predominantly of good

size and quality except where these are in dense, unthinned clusters at the base

of short whorls issuing from branch terminals of the previous year. With

increasing age of the disease in the tree, annual growth is greatly reduced,

branch terminals tend to die back, the crop is progressively less from year to

year, and in old cases the crop may be almost a total failure.

Muir is a superior drying variety and an excellent dessert peach. In 1946

there were 6,110 acres of Muir orchards in California. In acreage the variety

was third of the freestones and comprised about 10 percent of the freestone

peach acreage in the State. Progressive losses from Muir peach dwarf are known

to have been heavy in the Santa Clara Valley and in some other sections. Muir

peach dwarf may have been one of the factors that discouraged planting of

the Muir variety in recent years. From 1937 to 1946, inclusive, only 395 acres

of Muir plantings were made in California.

Host Range and Varietal Susceptibility

In nature Muir peach dwarf has been noted on only the Muir variety of

peach (Pnums pérsica) and on no other stone fruits. By graft inoculation

with buds from diseased Muir orchard trees the Muir peach dwarf virus was

successfully introduced into nursery trees of several peach varieties, on which

relative injury was as follows: Severe on Muir, Paloro, and Alexander; medium

severe on Lovell; slight on J. H. Hale; and absent on Elberta. It was also

introduced by graft inoculation into nursery trees of the following stone fruits,

all of which proved to be symptomless carriers: Nonpareil almond (P. amygdalus) on almond rootstock, Royal apricot (P. armeniaca) on apricot rootstock, Napoleon (Royal Ann) cherry (P. avhim) on mazzard (P. avium)

rootstock, mahaleb cherry (P. mahaleb) seedlings, and French (Agen) prune

(P. domestica) on myrobalan plum (P. cerasifera) rootstock. The virus was

introduced also into French prune and an unidentified variety of almond,

without producing symptoms, by top-working them on Muir peach trees

severely affected with Muir peach dwarf.

Symptoms

The most striking sj^mptom of Muir peach dwarf is to be seen in the growing

season, when the trees are in full leaf. The dwarfed, diseased trees (ñg. 21, A)

show a profusion of large, flattish deep-green leaves, rather closely appressed on

short twigs. By comparison, in summer a normal Muir tree (fig. 21, B)

displays lighter green leaves that are curved along the midrib and are evenly

disposed on naturally spaced, long twigs.

Shoot characters, apart from the fohage, are best seen in the dormant

season. Affected trees (ñg. 22, A) show a marked tendency to produce a

whorl of three to eight new shoots from branch terminals of the previous sea-

^'^ None of the results have been published. Therefore, the present account is given in

more detail than otherwise would be required.
VIRUS DISEASES OF STONE FRUITS 65

Figure 21.—A, Muir peach tree severely affected with Muir peach dwarf, with most

of the branch terminals, which had weakened and died back, pruned off, showing

large ilattish leaves and a dense foliage mass at base of tree; B, comparable unaffected tree.
Wl

iBK^I^^^^^^Mtf54^%t^ .. ..^:rÙL^%im m f^^^B

Ci

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a

o

o

Ö

H

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figure 22,—A, Old Muir peach tree severely affected with Muir peach dwarf, showing branch and twig characteristics; JB, comparable unaffected tree.
VIRUS DISEASES OF STONE FRUITS 67

son's growth. Lateral twigs are dwarfed and more closely spaced along the

extending limbs than is thecase on a normal tree (fig. 22, B).

After some years of the disease, scattered branch terminals weaken or die,

the dying sometimes extending downward along the limbs for a few feet. When

such limbs are pruned off, they are not replaced by new, upward-growing

shoots. Instead, the pruned trees are apt to produce a quantity of short,

branched, heavily leaved growth from the framework limbs; and sometimes

they produce suckers from the root collar. Such growth produces a very

heavy deep-green foliage mass about the base and framework arms of the tree.

Owing to the short internodes, the flowers on most of the diseased twigs

(fig. 23, A) are much closer together than on normal twigs (fig. 23, B). In

general, the internodes are apt to be extremely short for an inch or two, after

Figure 23.—A, Branch of Muir peach affected 'ïvith Muir peach d"warf showing tw^ig,

bud, and flower characteristics; B, comparable unaffected branch.

which they are somewhat longer and on some twigs may attain the normal

length. Frequently, at the end of the growing season the current season's

growth is considerably thickened and branched and may have extremely short

internodes, from which springs a whorl of twigs the following season (fig.

24, A). The short, diseased twigs are usually thickened throughout their

length and are apt to be pale green as compared with the reddish-brown color

of normal twigs. Failure to develop the brown color is probably due to dense

shade from the compact, heavy fohage.

The leaves from basal buds of diseased twigs are usually smaller than

normal, but are well formed. Leaves along the greater portions of the twigs

are as large as normal leaves or larger. Near the terminals of the season's twig

growth, the leaves on affected trees are not quite full size and tend to be

slender. All leaves on diseased trees are of a uniform green color; they show

no spots, mottling, or deformities whatsoever. They may remain green after
68 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Figure 24,—Muir peach nursery trees of the same age, sho"wing the stunting effect

of Muir peach d-warf: A, Diseased, 3 years after inoculation; B, unaffected.

normal foliage takes on autumnal coloration. Flowering and leafing in spring

may be slightly delayed on diseased trees.

Fruits on diseased trees ripen about the same time as normal fruits, and the

peaches may be of good size and quality if the trees are not too severely
VIRUS DISEASES OF STONE FRUITS 69

dwarfed. On the most severely diseased trees on which dying arms have been

cut back heavily, the peaches are large and misshapen, with a tendency to

develop spht pits. Fruit production is greatly reduced with increasing age of

the disease, and in the most advanced cases there may be only a dozen fruits

per tree.

Transmission and Natural Spread

Laboratory cultures failed to reveal the presence of a bacterial or fungus

parasite in the living tissues of afiiected trees. The disease was readily transmitted by grafting roots, bark, scions, or buds from diseased trees to the roots

or the shoots of normal Muir peach trees. Therefore Muir peach dwarf was

attributed to an infective virus.

Presence of the Muir peach dwarf virus in the varieties or species of peach,

almond, apricot, cherry, and plum graft-inoculated (p. 64) was determined

by budding back to uninfected Muir seedlings, which developed typical

symptoms of Muir peach dwarf. Although the French prune and the unidentified variety of almond top-worked on Muir trees severely affected with Muir

peach dwarf made extensive normal-appearing growth, buds from such growth

when indexed on uninfected Muir seedlings also induced typical symptoms of

Muir peach dwarf on them.

The natural vector of Muir peach dwarf virus has not been determined.

Natural spread of the disease was demonstrated in the Muir variety by annual

surveys in individual orchards.

Attempts were made by Cochran and Stout to recover Muir peach dwarf

virus from symptomless orchard trees of several sorts growing near heavily

diseased Muir orchards. At Morgan Fîill, Calif., a block of old Muir trees

almost 100-percent-affected with Muir peach dwarf was bordered by a row of

healthy-appearing old Elberta trees. Muir peach dwarf spreads in close-colony

formation, and it would be expected that some of the Elberta trees would be

carrying the virus even though they showed no symptoms of the disease. Each

of the Elberta trees in the row immediately adjacent to the diseased Muir

trees was indexed by budding on normal Muir nursery trees. None of the

index trees developed the disease, and it was concluded that at least in such

locations as the one investigated the hazard of natural spread of Muir peach

dwarf to Elberta trees was negligible.

Healthy-appearing old almond trees in an orchard row adjacent to a heavily

diseased Muir peach orchard at Chico were indexed for the presence of Muir

peach dwarf virus. None of the Muir index trees developed the disease.

Similarly, old orchard trees of apricot and French prune adjacent to severely

diseased Muir orchards were indexed. In no instance did the Muir index trees

develop Muir peach dwarf.

Under maximum locational opportunity for natural spread of Muir peach

dwarf, the causal virus did not find its way from heavily diseased Muir

orchards to adjacent orchards of Elberta peach, almond, apricot, and French

prune. Nevertheless, all of these sorts are known to be symptomless carriers

of Muir peach dwarf virus if the latter is introduced by graft inoculation. It

has been shown that some peach varieties other than Elberta will develop

symptoms of Muir peach dwarf following graft inoculation and that symptom

manifestation will vary from mild to severe, depending upon the peach

variety. However, natural occurrence of Muir peach dwarf on any of these

peach varieties has not been reported.

Within the limits of the present knowledge of Muir peach dwarf as it occurs

891793°—51—7
70 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

in nature, this very interesting and unique virus disease appears to be confined

to the Muir peach variety and it has not been reported outside Cahfornia.

Incubation Period

As determined by graft inoculations the incubation period of Muir peach

dwarf is less than 1 year. When diseased scions were grafted on healthy Muir

peach orchard trees in winter, symptoms began to develop in the vicinity of

the inoculum the following spring. Normal Muir nursery trees grafted in

summer with buds or bark from diseased trees developed symptoms of Muir

peach dwarf the next growing season.

Control Measures

Propagating material of the Muir peach variety should be selected at a

considerable distance from diseased Muir trees, and preferably it should come

from districts entirely free of the disease.

In orchards only trees of the Muir peach variety are known to contract Muir

peach dwarf; diseased trees are very easy to identify; spread is slow and occurs

predominantly in close-colony formation; and the incubation period, as determined by graft inoculation, is less than one year. Therefore, under such

favorable conditions for rapid detection of infected trees, well-directed eradication procedures should be very effective in controlling the disease.
RING SPOT

By L. C. CocHRAN, LEE M. HUTCHINS, J. A. MILBRATH, GILBERT L. STOUT, and S. M. ZELLER

Names of the Disease

Ring spot was originally described on peach (62). The name was applied

because ring and spot symptoms are consistently produced on peach and most

other host plants. Probably the first record of the disease was made by

Valleau (242). In working with yellows and an unidentified trouble on plums,

he described symptoms on inoculated peach seedlings which indicate the presence

of forms of the ring spot virus in the complex. The disease was probably also

encountered by Thomas and Rawlins (23 3) in work with the buckskin virus

and recorded as a mosaic of mazzard cherry. Later pubhcations on what may

be the same virus, or forms of it, refer to a disease produced on sour cherry as

necrotic ring spot (91, 163, 164) and to one on sweet cherry as lace leaf

(256),^^ It is possible that tatter leaf on sweet cherry described by Willison

and Berkeley (249) may also be caused by the ring spot virus. The production

of symptoms on midsummer leaves of trees affected with necrotic leaf spot of

peach (49) differentiates this disease from ring spot, which produces symptoms

only on leaves formed in the spring.

Names of the Causal Virus

No Latin binomial has been applied to the causal virus except that the

virus causing ring spot on sour cherry has been referred to as Annulus cerasae

by Hildebrand (91). Under the naming system proposed by Fawcett, the

name would be ''Prtmivir chctcmmacnlum.'' Until an international system of

virus nomenclature is adopted, the authors prefer to use the name "ring spot

virus."

History and Geographic Distribution

The wide distribution of the ring spot virus indicates that it probably has

been present for a long time. One reason why its presence was not recognized

earlier is its habit of chronic existence in most hosts without causing visible

symptoms of the disease. The production of necrosis in various plant organs

in the early stages of the disease has caused confusion with fungus and

bacterial diseases, especiall)^ those of the leaf-spot and shot-hole types. Apparently the ring spot virus is actually a group virus composed of many forms,

which because of their various effects on host plants have been reported in

some cases as the causes of separate diseases.

Ring spot virus is prevalent in commercial peach orchards in western

United States, where it exists in trees mostly without leaf symptoms and

similarly in nursery stock propagated from them. The virus is also very commonly existent in almonds, prunes, plums, apricots, and cherries and has been

recovered from native chokecherry, chickasaw plum, wildgoose plum, American plum, and escape plum seedlings. It is probably most widespread in

cherries, being nearly universal in commercial orchards in western United

States (59, 156, 157), The lesser occurrence in peach and other stone fruits

in sections where cherries are not grown points to cherries as a primary

"^^ Reeves, E. L. Unpublished data.

71
72 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

reservoir ()8). Moore and Keitt (163) reported that the necrotic ring spot

virus is so prevalent in sour cherries in Wisconsin that they have been unable

to find a source of sour cherry yellows virus free from it. Hildebrand reported ring spot on cherries (84, 91, 9^) and on Italian Prune (92) in New

York. Willison and Berkeley (249), in describing symptoms of tatter leaf of

sweet cherry, and WilHson, in describing a line pattern virosis of Shiro plum

(247) and strains of the prune dwarf virus (246), described symptoms produced on peach and other hosts similar to those caused by ring spot.

Economic Importance

The deleterious effect of ring spot is difficult to measure because the different forms of the virus have different effects, because damage on most

hosts is limited to the acute stages of the disease, and because the horticultural

varieties are affected differently. Symptoms are rare and obscure on most

varieties of apricot, plum, and prune. Some forms of the virus diminish the

crop on sweet and sour cherries during the initial stages of the disease and

reduce the vigor of sweet cherries in the chronic state. Milbrath and Zeller

(156, 157) showed that the virus produces dire and serious effects on oriental

flowering cherries. Almonds are often strikingly mottled, but no data are

available on reduction of crop yields. Damage to peaches varies with varieties, and with most forms of the virus it is Hmited to early stages of the

disease. Varieties as severely injured as Rio Oso Gem when affected with

some forms may be so severely killed back that the crop loss extends into succeeding years because of the loss of fruiting wood. Experimentally J. H.

Hale, Early Hale, Rio Oso Gem, Rochester, and Fay Elberta have been shown

to be permanently reduced in vigor when affected with severe symptomproducing forms of the virus.

Host Range

The virus has been recovered from many varieties of naturally infected

peach {Pfîums pérsica), sweet and sour cherries (P. avhim and P. cerasiis),

Japanese plum (P. salicina), domestica plum (P. domestica), almond (P.

amygdalus), and apricot (P. armeniaca). It has also been recovered from

native stands of American plum (P. americana), chickasaw plum (P. angustifolia), wildgoose plum (P. mtmsoniana), sand cherry (P. ptunila), eastern

chokecherry (P. virginiana), and desert apricot (P. fremontii), from escape

myrobalan plum (P. cerastfera) seedlings, from Rosa sp., and from Japanese

apricot (P. imime). Experimentally ring spot virus has infected all the species

of the genus 'Prunus on which it has been tried. The following species have

been graft-inoculated and the virus has been recovered as evidenced by production of symptoms on peach after graft inoculation with affected material from

the respective species: Peach, many varieties; mazzard cherry (P. avitun) seedlings; mahaleb cherry (P. mahaleb) seedlings; chickasaw plum; myrobalan

plum; almond; western chokecherry (P. virginiana var. demissa) ; domestica

plum; Japanese plum; apricot; damson plum (P. insititia) ; Japanese apricot;

desert apricot; flatwoods plum (P. mnbellata) ; tangut almond (P. tangutica) ;

David peach (P. davidiana); Bokar plum (P. hokhariensis) \ Manchu cherry

(?. tomentosa) ; oriental flowering cherry (P. serrulata) ; and apple (Malus

sylvesfris).

Symptoms

The symptoms on stone fruits are variable and can be arranged in a gradient

due to the differential resistance of host varieties and species and to the existence of and differential effects of forms of the virus (57), On some host
VIRUS DISEASES OF STONE FRUITS 73

varieties and species and with some virus forms symptoms are predominantly

chlorosis; on others symptoms include stunting and necrosis of leaf, cambial,

cortical, and bud tissues. In most hosts leaf symptoms, vs^hether chlorotic or

necrotic, include rings, spots, and patterns made up of rings and spots. The

size of rings is usually inversely proportional to the number present. In all

hosts symptoms are more pronounced in the early stages of the disease, and

in many hosts visual leaf symptoms occur only during the first year of infection. Some hosts become infected and retain the virus without any visual

symptoms. Some hosts develop leaf symptoms when infected with certain

forms of the virus but not with others. In some hosts affected with certain

forms of the virus visual symptoms occur annually; in such cases symptoms

are usually more severe during the acute stages of the disease than during

succeeding ones.

Peach.—Peach varieties differ in response to the ring spot virus. In one

series of hybrid seedlings inoculated with a single form by Cochran some

showed only a few obscure rings; others developed numerous rings, shot hole,

bud killing, and tip dieback; and still others were entirely killed. Of the

commercial varieties tested, Rio Oso Gem is one of the most severely injured

(pi. 13, A). Affected trees in the acute stages are retarded; many buds, both

flower and leaf, die when partially open; and past-season terminal growth may

be killed and twig blight similar to that characteristic of brown rot, caused

by Sclerotinia spp., may result. On some twigs not entirely killed, necrotic

cankers form at the nodes and around the base of lateral buds. Leaves arising

from buds partially killed show all grades of patterns from chlorosis to

crowded ring patterns and shot hole {^g. 25),

On varieties having red-colored fruit, like Rio Oso Gem, J. H. Hale, and

Rochester, the borders of rings and necrotic spots develop red margins (pi.

13, C). Initial leaves having necrotic rings or crowded ring patterns are

usually shed during the first few weeks of growth {iig* 26). Trees severely

killed back usually develop sucker shoots on the main trunks or rootstocks

and appear to recover, and those affected with most forms of ring spot virus

are devoid of leaf symptoms during the remainder of the season and in succeeding years (pi. 13, B). Fay Elberta peach trees inoculated by Cochran in

series with forms varying in severity of symptom production were hedgerowpruned 3 years after inoculation and observed for vigor. The trees which

originally were severely affected made only approximately two-thirds the

length of growth after pruning that the checks did (pi. 13, F), whereas those

slightly affected equaled the checks in growth.

Fay Elberta, Late Elberta, Krummel, Rochester, and J. H. Hale are also

severely affected. Nursery trees of these varieties inoculated with virus forms

that had produced a gradient of symptoms were correspondingly affected.

Some forms obtained from sweet cherry completely killed the inoculated

trees. Others caused severe necrosis of buds, tip dieback (pi. 13, £), and

killing of cambial and cortical tissues at the inoculation point, the last resulting in splitting and cracking of the bark (pi. 13, D) and often girdUng

of the entire arm. Trees inoculated with so-called mild forms are usually

slightly retarded and pale in color. They develop scattered leaves with obscure

spot and ring patterns, but they soon recover by shedding or greening of such

leaves.

Some varieties such as Sims, Paloro, Tuskena (Tuscan), and Lovell are

only mildly affected by forms which severely injure J. H. Hale. On these
74 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Figure 25.—A, Ring-spot-afîected leaves of Lovell peach, showing rings, spots, and

chlorotic patterns. B, Affected leaves of July Elberta peach on which the symptoms

are predominantly chlorosis but on wrhich rings and shot hole occasionally occur;

leaves like third to fifth from the left are usually shed during the acute stages,

and ones like the others become green as the season progresses.

varieties symptoms often consist of scattered ring and shot-hole patterns

which may persist late into the growing season. Likewise, leaf symptoms

produced by virus forms that cause mild effects on the more seriously damaged

varieties may persist longer than those accompanying severe injury.

Plum.—On Japanese- and domestica-type plums symptoms of ring spot
VIRUS DISEASES OF STONE FRUITS 75

Figure 26.—Elberta peach in midsummer after showing acute symptoms of ring spot

in spring. The bare twigs and thin foliage show where the buds and twigs have

died and been shed.

are generally absent or mild. Some virus forms produce no symptoms on any

varieties, and others produce them on only certain ones. Rings and chlorotic

patterns were produced on French (Agen) and Hungarian prunes and on

Shiro and Beauty plums. Myrobalan seedlings vary in reaction from no

symptoms to chlorotic ring and fish-net patterns and in a few cases to necrotic

spots and shot hole. No symptoms were seen on either bud-inoculated or

naturally infected wildgoose and chickasaw plums. During acute stages of

infection vivid chlorotic ring and mottle patterns were produced on Bokar

and American plums.
76 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Almond, apricot, and David peach.—On almond most forms of the virus

cause ssymptoms that vary from chlorotic, crowded ring to oak-leaf and

necrotic patterns (fig. 27, B). Expression is most striking in the Ne Plus Ultra,

Figure 27.—A, Leaves of mazzard cherry affected "with ring spot slioTving rings, shot

hole, and chlorotic and necrotic patterns; B, affected Nonpareil almond leaves showing ring spot and chlorotic patterns in contrast ^ï^ith unaffected leaves at left.

Nonpareil, I. X. L., Drake, and Peerless varieties in descending order. The

disease is very prevalent in commercial orchards; and, while symptoms are

always more evident the first year of the disease, they are often persistent in

succeeding years in scattered leaves.

Only a small proportion of the virus forms cause symptoms on apricot.

These vary from sharply defined rings to oak-leaf patterns and necrosis.

Occasionally, forms which cause tip blight and shot hole have been found.
VIRUS DISEASES OF STONE FRUITS 77

On tangut almond and David peach the symptoms were similar to those on

Bokar and American plums.

Cherry.—The ring spot virus is nearly universally present in commercial

orchards of sweet and sour cherries in western United States, as evidenced by

transmission to peach and oriental flowering cherries. Symptoms observed

on sweet cherry in commercial orchards vary from chlorotic ring patterns to

shot hole and lace leaf. On some trees symptoms persist annually, but arc

not as pronounced as first-year symptoms. Most sweet cherry trees from which

transmission was effected were showing no symptoms when the inoculum

was taken. Mazzard and mahaleb cherry seedlings inoculated with diseased

peach tissue in the fall produced typical symptoms at the beginning of growth

the following spring, varying from sharply defined rings and crowded ring

patterns to shot hole and lace leaf (fig. 27, A). Individual seedlings, especially mahaleb, reacted variably when inoculated with material from a single

source. Symptoms like those observed in the orchard have not been obtained

B

Figure 2S.—A Shiro-fugen oriental flowering cherry stem budded with two sweet

cherry buds (upper virus-free and lower infected "with ring spot virus): A, Without

bark removed; B, with bark removed to show necrosis of the tissues adjacent to

the infected bud, the callus union, and the start of growth of the virus-free bud.
78 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

by experimental infection of sour cherry, since no virus-free sour cherry stock

was available to the authors when these studies were made.

Milbrath and Zeller (Í56, 157) described the symptoms of ring spot and

latent viruses on the Kwanzan and Shiro-fugen varieties of oriental flowering cherry. These varieties show promise as excellent diagnostic hosts in that

they are seriously damaged by many if not all forms of the virus. On Shirofugen nearly all forms of the virus are apparently parenchyma-limited. When

trees are inoculated with diseased buds the virus moves slowly from these

diseased buds into the surrounding tissue. The tissue invaded becomes

necrotic (fig. 28), and if left unimpeded the virus will eventually move down

the stem, killing the whole plant. If the branch is removed to a point below

any necrotic tissue, the progress of the disease is stopped; thus apparently

the virus is removed. A single tree of the Shiro-fugen variety can be used to

index a large number of orchard trees by spacing the inoculation buds and

taking readings before girdling takes place. In Kwanzan the virus is more

completely systemic (fig. 29). If buds from a tree under test show no

Figure 29.—A, Branch from normal Kwanzan oriental flowering cherry tree; B—D,

branches from comparable trees inoculated with three forms of the ring spot virus

producing a gradient of symptoms: B, Mild; C, intermediate; D, severe.

reaction on Shiro-fugen they are tested on Kwanzan. Milbrath and Zeller

found a few forms which react on Kwanzan but not on Shiro-fugen and

conversely.

Transmission

Transmission has been experimentally effected only through tissue grafting.

Cochran (58, 59a) showed that the virus passes through a low percentage of
VIRUS DISEASES OF STONE FRUITS 79

the seeds of mazzard cherry and of Lovell and Rio Oso Gem peaches; ring and

mottle patterns were produced on the mazzard seedhngs, but no symptoms

were seen on the peach seedhngs. Cation (^1) found upward of 10 percent of

mahaieb cherry seedhngs grown from commercial seed carrying the ring spot

virus. The infected mahaieb seedlings showed no symptoms, and the presence

of the virus was demonstrated by indexing on peach. Spread recorded by

Cochran and Stout in commercial peach and almond orchards varied in rate in

different years.

When peach buds containing the ring spot virus are budded on healthy

Lovell peach seedlings or trees of various peach varieties, the buds commonly

die without making any perceptible union, yet a high percentage of the

seedlings or trees become infected. Conversely, when healthy buds of a

variety are placed on a stock containing the virus, they likewise often fail

to live. When buds containing the virus are placed on stocks also containing

the virus there are no shock symptoms and no abnormal number of bud

failures. Bud failure when the bud is carrying the virus and the stock is

healthy is somewhat variable, depending largely on two factors: the relative

severity of effect of the form of the virus present as expressed on severely

damaged varieties and the relative susceptibility of the seedling or variety

understock to injury.

A larger percentage of peach buds containing severe-symptom-producing

forms of the virus will fail on all peach varieties than of buds containing only

mild ones. Correspondingly, even buds containing only so-called mild forms

may fail on peach varieties which are strong reactors. Milbrath and Zeller

(156) showed that healthy buds of oriental flowering cherry fail when they

are placed on mazzard seedlings or cherry varieties containing the ring spot

virus. No appreciable difference was noted in the number of failures of

apricot, almond, and plum buds carrying ring spot virus and of those free

from it when they were placed on Lovell peach. The failure of buds is

believed to be due to the killing of newly invaded cells of the stock adjacent

to the diseased bud shield, which prevents union of shield and stock.

Incubation Period

The incubation period varies with the condition of the tree inoculated.

Peach trees inoculated while breaking dormancy sometimes develop symptoms

in new leaves at terminals in as short a time as 10 days. Trees just reaching

full leaf usually require up to 3 or 4 weeks, and the resulting infection is

usually limited to a portion of the tree. Trees inoculated as late as June to

August may not show symptoms in leaves until the following growing season; but, when infected with forms of the virus which cause canker and

bark necrosis, they may develop sunken bark cankers adjacent to and usually

below the inoculation point during the current season. Trees inoculated in

the fall just before the bark becomes tight develop symptoms on the first

growth of the following season. The virus commonly invades all parts of

small nursery trees during the first season, but symptoms on large trees are

often limited to the inoculated arm and the basal portion of adjacent arms.

Control Measures

The almost universal latent occurrence of the ring spot virus, the evidence

of its rapid tree-to-tree spread in many stone-fruit orchards, and the lack

of evidence that the virus is associated with serious general reductions in

yield make the feasibility of control by ordinary methods questionable. Some

workers feel that reduction in crop during the acute stages of the disease and
80 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

the possible reduction in vigor of trees in the chronic stages are worthy of

efforts to furnish foundation stock free of the virus for the nursery trade.

Remarks

The widespread occurrence of the ring spot virus in many hosts^ especially

in the Pacific Northwest, is evidence that it has been present for a long time.

On peach, ring spot has with little doubt been confused with the twig

blight symptom of brown rot, caused by Sclerotinia spp., and the twig blight

stage of peach blight, caused by Coryneum carpophihim (Lev.) Jauch. The

latent character of ring spot in the chronic state in many hosts has allowed

the causal virus to be carried as a contaminant with other viruses in tissue

transmission and has resulted in confusion, especially in host-range studies.

If two viruses exist in a single host, only one of which has effected symptoms,

and both are transferred in tissue to a second host, there is no basis for ascertaining which is responsible for the symptoms in the second (55).

The relation of ring spot and necrotic ring spot of sour cherries needs more

study to ascertain whether they are identical. The virus causing ring spot

as expressed on peach is universally present in sour cherry on the west coast,

and no healthy sour cherry material was available during early studies for

inoculation studies on sour cherry. Sour cherries carrying ring spot virus

without symptoms develop no symptoms after inoculation with peach buds

carrying the virus. Hildebrand (54, 5Í), Rasmussen and Cation (176),

Keitt and Clayton (124), Berkeley and Willison (9), and Willison, Berkeley,

and Chamberlain (250), working with sour cherry yellows, described

symptoms on peach and other hosts similar to those of ring spot; this suggests that the ring spot virus was present in their cultures or is a component

of the cause of sour cherry yellows. Moore and Keitt (163, 164) showed that

necrotic ring spot virus is a single entity but were not able to obtain a culture

of sour cherry yellows free from it. It seems logical, on the basis of wide

occurrence, variation in expression of ring spot, and the interhost-transmission results obtained by various workers, that necrotic ring spot of sour cherry,

tatter leaf of sweet cherry, and possibly others, already described, belong to

the ring spot group.
PEACH NECROTIC LEAF SPOT

By DONALD CATION

Name of the Disease

This disease, originally described on peach (49), was called necrotic spot

to distinguish it from ring spot (62).

Name of the Causal Virus

No Latin binomial has been apphed to the causal virus, but for convenience it may be referred to as necrotic leaf spot virus.

History and Geographic Distribution

Necrotic leaf spot v^as first observed in 1940 on two Liberta and two

Carman peach trees which had been inoculated in the fall of 1939 during a

routine indexing test with buds from a Windsor sweet cherry tree located in

East Lansing, Mich. Further inoculations from these peach and Windsor

cherry trees to additional seedlings and varieties of peach consistently resulted

in the same pattern of symptoms, which were different from the ring spot

symptoms of the types described by Cochran and Hutchins ( 62 ), Berkeley

(8), Willison and Berkeley (249), and Hildebrand (91). Additional indexings from sweet cherries in Michigan indicate that the virus of necrotic leaf

spot is frequently present as a latent virus in sweet cherry and as a result of

distribution by nurseries it may be widespread in that species. The virus is

frequently found in sweet cherries in California as indicated by indexing on

peach. ^^

Economic Importance

The harmful effects on peach and cherry have not been measured, but the

disease appears to be of small consequence.

Host Range

The disease has been transmitted to seedlings and seven varieties of peach

(Pruntcs pérsica), namely, Liberta, Carman, J. H. Hale, Golden Jubilee,

South Haven, Halehaven, and Fertile Hale, and causes symptoms on them.

No symptoms have been observed on the varieties of sweet cherry (P. avium)

and sour cherry (P. cerasus) tested, but the sweet cherry varieties tested were

found to be symptomless carriers.

Symptoms

Peach.—In the orchard, light-brown, membranous, dead areas appear only

on young, unfolding leaves of affected peach trees (ñg. 3 0). The largest

numbers of characteristic necrotic spots occur on unfolding leaves during

July, but a few typical spots may be found earlier. Traces of necrotic spotting are occasionally observed in the spring on the first-formed leaves. The

necrotic spots are usually round and may occur on any part of the leaf blade.

Occasionally a long, narrow area along the leaf margin is affected. Rarely

more than one or two leaves on any particular growing shoot are affected.

The dead tissue soon falls out, leaving a clean-edged margin. Other parts of

the leaves are of normal color. Affected leaves do not drop prematurely.

Occasionally faint chlorotic spots accompanied by leaf distortion are seen

Conversation with L. C. Cochran at Behsville, Md., August 26, 1949.

81
82 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Figure 3 0.—Young leaves from peach trees affected "with necrotic leaf spot.

early in the season, but these symptoms occur on relatively few leaves. Inoculations by budding of peach trees in August do not result in delayed foliation,

dieback, or bark necrosis in the following spring, although such symptoms are

common on peach inoculated with certain strains of ring spot virus ( 8, 62, 91).

In 1947 seedling peach trees in the nursery row inoculated with necrotic

leaf spot virus did not show delayed foliation and dieback of the previous year's

growth as did those inoculated with the strains of ring spot virus, but they

did show dieback of one or more shoots of the current year's growth 2 to 3

weeks after bud break (May 23). In June and July typical necrotic spot

developed on some of the leaves on other shoots.

Inoculation of Fertile Hale peach trees with buds of Windsor cherry containing the necrotic leaf spot virus at the time of growth initiation resulted

in symptoms not unlike those resulting from strains of ring spot virus. The

symptoms on peach in the greenhouse consisted of dieback of some of the new

shoots and chlorotic and necrotic ring spots on leaves. The inoculum may

have been contaminated with strains of the ring spot virus (59).

Cherry.—Certain symptomless Windsor, Black Tartarian, and Napoleon

(Royal Ann) sweet cherry trees were shown to be carriers of the virus by

indexing on peach. Inoculations of the same varieties of cherry did not

result in symptoms. Inoculations of Montmorency sour cherry trees resulted

in no symptoms, but trees from the same lot were later shown to be carrying

ring spot virus similar to that reported by Berkeley (8) and Hildebrand (91).

Diagnostic or Unusual Characteristics

Necrotic leaf spot is distinguished by the necrotic areas on new leaves un-
VIRUS DISEASES OF STONE FRUITS 83

folding in midseason and by the absence of chlorotic rings, bark necrosis, dieback of previous season's growth, and delayed foUation which generally accompany ring spot diseases in peach. The chronic nature of the disease as

characterized by the appearance of symptoms year after year and in midsummer

is also at variance with the ring spot diseases reported (S, 62, 91, 249),

Transmission

Transmission as far as known is effected only by budding or other forms

of the grafting process. Indications of natural spread have not been observed.

incubation Period

Inoculations in August in the field result in symptoms the following season, 9 to 10 months later, but symptoms are obtained in 3 to 5 weeks when

trees just breaking dormancy are inoculated in the greenhouse.

Control Measures

The disease can be avoided in the propagation of sweet cherry by selecting

scion wood from trees previously determined to be disease-free by indexing

on peach. Peach trees affected with necrotic leaf spot should not be used as

a source of propagating material.
ASTEROID SPOT

By L. C. CocHRAN and C. O. SMITH

Names of the Disease

The name ''asteroid spot" was given to this disease because of the similarity

of the leaf spot symptoms on peach to small, star-shaped splotches (65). The

disease is known locally in Texas as stipple spot, but it has no relation to the

noninfectious condition on myrobalan plum seedlings described by Hildebrand

(94) under the name "asteroid spot."

Names of the Causal Virus

Marvtor astri Holmes is the only Latin binomial which has been assigned to

this virus. It is referred to here by adding the term "virus" to the common

name of the disease; thus, **asteroid spot virus."

History and Geographic Distribution

Asteroid spot was first seen on the peach understock of some trees in a

rootstock experiment at the Citrus Experiment Station, Riverside, Calif. The

occurrence in commercial orchards in California was first noted in 1939 and

called to the authors' attention by R. L. McClain, who suggested its identity

with a disease widely existent in Texas and temporarily designated by Lee

M, Hutchins as ''stipple spot." Further studies of asteroid spot showed

variation in symptom expression due to the presence of virus forms, and it

seems likely that stipple spot, as well as others, is the same as asteroid spot.

Asteroid spot is widespread in peach in Texas and westward to southern California. Two affected trees reported in North Carolina were traced directly to

infected nursery stock originating in Texas {')'>)' Occasional affected trees

have been seen in Oregon, Utah, and Colorado. One case was seen in a very

old peach tree, probably a Spanish seedling, growing in the courtyard of the

Convent de Monte Cristo, Puebla, Mexico.

Economic Importance

There is very little evidence that asteroid spot is the cause of any appreciable

damage on any of the hosts. It may exist in certain hosts without causing

symptoms, and it must thus be regarded in the light of a possible contaminant

in host-range studies.

Host Range

Symptoms of asteroid spot have been seen on peach {Vrnnns pérsica),

nectarine (P. pérsica var. nectarina), almond (P. amygdahis), apricot (P.

armeniaca), Japanese plum (P. salicina), domestica plum (P, domestica),

Japanese apricot (P. miime), and ansu apricot (P. armeniaca var. ansu).

Peach, apricot, Japanese plum, and almond have been experimentally infected.

Symptoms

On peach symptoms first show about 6 weeks after growth starts, but they

become most pronounced about August. Spots begin as small, translucent

light-green flecks in the darker green of fully expanded leaves, giving the

appearance of yellowish-green paint on the leaves {£.g. 31). As the leaves

mature, scattered leaves turn yellow but the fully formed spots remain yellowish green, thus reversing the color contrast. Spots vary in size, the size

being inversely proportional to the number present. Occasionally some of the

84
VIRUS DISEASES OF STONE FRUITS 85

Usure 31.—Peach leaves affected with asteroid spot: A, J. H. Hale, showing typical

spots and occasional necrotic ones; B, Lovell.

larger spots have green centers and thus are really rings. On some leaves large,

angular, chlorotic blotches form along the veins as if the veins were ruptured

and had flooded the bordering tissue.

In field comparisons white-fleshed peach varieties appear to develop more

pronounced symptoms than yellow-fleshed ones. Similarly nectarines, which

are white-fleshed, are strongly affected. On orchard trees symptoms are

usually limited to chlorotic spots, but necrosis has been seen on inoculated

J. H. Hale peach trees during acute stages. Symptoms are more pronounced

during the initial year of the disease, but affected trees show symptoms annually. The size, intensity, and number of spots in inoculated peach trees

varied with the sources of the virus, indicating the existence of forms of the

On Japanese-type plum symptoms vary with varieties, but resemble closely

SSIZSJ"—51—s
86 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

those on peach. Late Santa Rosa (fig. 32, A) was strikingly affected, whereas

regular Santa Rosa, Wickson, and Satsuma plums were less affected. On

inoculated almond and French (Agen) prune the symptoms were obscure.

On apricot (fig. 32, ß) symptoms were well developed during the acute stages,

but they failed to reappear after the trees became thoroughly affected. Transmission from naturally affected plums and peaches to apricot gave variable

Figure 32.—Leaves of (A) Late Santa Rosa plum and (B) Royal apricot affected

-witli asteroid spot, except for normal leaf at center of bottom ro^r.
VIRUS DISEASES OF STONE FRUITS 87

results, inoculum from some producing well-defined symptoms and that from

others obscure symptoms or none.

Transmission and Incubation Period

Transmission from peach to peach by inoculation with bark shields in the

fall usually results in symptom expression in fully expanded leaves 6 to 8,

weeks after the beginning of spring growth. Transmission was effected experimentally in 8 weeks when infected scions were grafted on peach trees

which were breaking dormancy. Translocation of the virus appears to be

slow, and initial symptoms may be obscure but may become more intense as

more tissue is involved. The widespread occurrence of the disease in some

orchards is indicative of natural spread, but, if this takes place, the vector is

unknown.

Control Measures

Available data do not show that the asteroid spot causes crop damage of

any consequence, but it is reasonable that it should be avoided in the establishment of nursery foundation stocks.

Remarks

Asteroid spot is chiefly important becaitse of the confusion that may

result in interpretation of experimental work when the causal virus is carried in the cultures as a contaminant.
GOLDEN-NET

By E. W. BoDiNE and L. W. DURRELL

Other Common Names of the Disease

None.

Name of the Causal Virus

Golden-net virus.

History and Geographic Distribution

Golden-net was found first in Colorado in 1937 on apricot and plum and

in 1939 on Elberta peach {36, 40). It has also been observed in California.^'

Economic Importance

Golden-net virus appears to cause little damage to peach and plum. It

does, however, cause severe damage to apricot. To date, however, little

natural spread of the golden-net virus has been observed in apricots.

Host Range

As far as known golden-net has been found only on Elberta peach (Prtmus

pérsica) and its seedlings, on an unidentified variety of apricot (P. armeniaca),

and on Satsuma plum (P. salicina).

Symptoms

Peach.—The characteristic symptom on peach trees is the marginal yellowing

of the veins of the affected leaves (fig. 33). Because of this outstanding

Figure }i.—Elberta peach leaf affected "with golden-net.

constant symptom the disease is called golden-net. Occasionally irregular

primuline yellow areas occur on some leaves. No retardation of twig growth

is apparent, and fruits on affected trees are normal in size, shape, and color.

Apricot.—The disease affects the apricot tree more severely than it does the

peach. The leaves frequently show an abnormal crinkling and mottling along

and between the veins. The current-shoot growth of diseased trees is distinctly stunted. After the stone-hardening period, the fruits become misshapen and exhibit a marked bumpiness.

' Thomas, H. Earl. Unpublished data.

88
VIRUS DISEASES OF STONE FRUITS 89

Phim.—The only symptom on Satsuma plum consists of an inconspicuous

marginal mottle, frequently associated with irregular yellow areas on some of

the leaves on infected trees in the early spring.

Transmission

Transmission has been accomplished only through budding.

Incubation Period

The incubation period after the insertion of diseased buds varied from 9

to 18 months.

Control Measures

It is not felt at present that this disease justifies control by diseased-tree

removal, because of the small amount of damage on affected peach and plum

and the lack of evidence of natural spread among apricots.
PEACH CALICO

By EARLE C. BLODGETT and E. L. REEVES

Name of the Disease

"Leaf variegation" is sometimes used for peach calico, but more properly

this name refers to the nontransmissible, or chimera, type of disease.

Name of the Causal Virus

Peach cahco virus.

Geographic Distribution

One naturally diseased tree (19) and two other trees possibly diseased have

been seen in Canyon County, Idaho. Nursery trees were experimentally infected in Latah County. Peach cahco has also been reported in Washington

(1S4), Two diseased trees have been observed in King County and four in

Chelan and Douglas Counties.

Economic Importance

Peach cahco at present is regarded as of very minor importance. Losses

might result, however, if nursery stock was propagated from an infected tree,

since a goodly portion of the stock might show symptoms and be unsalable.

The total effect of the disease on a tree is minor after the initial stages.

Host Range and Varietal Susceptibility

Rochester, Early Crawford, and Liberta varieties of peach (Pmniis pérsica)

were found naturally affected. Transmission to the Liberta variety and to

peach seedlings has been effected with buds. Three J. H. Hale peach nursery

trees failed to show symptoms when inoculated. Thomas and Rawlins (23 3)

reported that almond calico is transmissible to peach and cherry, but Thomas

stated that he does not believe peach calico found in Idaho is the same as

calico on almond. ^-'

Bing (P. avium). Montmorency (P. cerastis), and May Duke (hybrid)

cherries, Moorpark apricot (P. anneniaca), Itahan Prune (P. domestica),

and Ne Plus Ultra almond (P. amygdahts) were inoculated in limited trials,

but no symptoms developed on any of these. When the inoculation buds grew

into shoots, leaves on them showed typical symptoms. No data are available

to indicate whether the varieties listed are symptomless carriers.

Symptoms

Symptoms of peach cahco may appear as the leaves unfold, showing in the

early stages a motthng, or mosaiclike, pattern. Later the hght-green areas

enlarge, principally along the veins, and eventually the color changes to a

brilhant yellow or almost papery white (fig. 34). Not all leaves show symptoms. Creamy-white streaks or nonuniform patterns develop on affected twigs.

The margins of these streaks or areas may be pink. The difference between

cahco and leaf variegation (nonvirus) is fairly distinct. In leaf variegation

the affected areas are rather sharply delimited with at least three distinct shades

of green, while in cahco the veins are yellow and there is a gradient of color

in leaf tissue from green to yellow or white (24).

Affected trees usually show fewer and less distinct symptoms the second or

^^ Thomas, H. Earl. Correspondence.

90
VIRUS DISEASES OF STONE FRUITS 91

Figure 34.—Peach leaves affected with calico.

third year of the disease and may finally even become symptomless. Fruits on

affected branches may show symptoms when they are about the size of walnuts.

The peaches are smaller, shorter, and more nearly round than normal ones.

There may be irregular patches of creamy-white tissue showing through the

pubescence. In a few cases the affected areas are orange, shading into dull

red.

Diagnostic or Unusual Characteristics

Careful examination of leaf symptoms and comparison with symptoms of

leaf variegation are essential in diagnosis. Of particular interest is the evidence, both on the original tree and on experimental stock, of erratic,

unpredictable behavior of the peach calico virus.

Reeves found that 10 of 11 Elberta peach trees receiving inoculating buds

from an affected Early Crawford tree exhibited leaf symptoms of peach

calico the first year after inoculation; only 1 of the 10 trees showed leaf

symptoms the second year after inoculation and these were meager; and

none exhibited symptoms the third year. Similar results were obtained with
92 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

buds taken from an aííected Rochester tree budded into healthy Elberta trees.

Buds taken from 1 previously inoculated Elberta tree the second year after

infection (a tree which had exhibited symptoms of calico the first year but not

the second) resulted in the reproduction of symptoms on 1 of 10 trees receiving

such inoculating buds. This preliminary test might indicate that the virus

could be latent but of limited distribution in a peach tree not exhibiting

foliage symptoms, but further tests should be made to establish these points.

Transmission

Positive transmission has been obtained by bud inoculation from peach to

peach, but many attempts were unsuccessful. It appears that movement of

the virus in a tree is slow and that the extent of distribution is uncertain.

Incubation Period

Trees budded in the fall with calico-infected buds exhibit symptoms on

the scion early in the spring, but visible infection of the leaves of the stock

may not appear until past midsummer.

Control Measures

Infected trees should be removed, and budwood from healthy trees should

be used for propagation purposes.

Remarks

Observational and experimental evidence indicate that at present peach

calico is of more academic interest than economic importance. Further

study is desirable because of its unusual characteristics and erratic behavior.
PEACH BLOTCH

By R. S. WiLLisoN

Other Common Names of the Disease

None.

Name of the Causal Virus

Peach blotch virus.

Geographic Distribution

Peach blotch has been found on single trees in two widely separated orchards

on Niagara Peninsula, Ontario, Canada.

Economic Importance

Peach blotch is of minor importance.

Host Range

So far the only species known to be attacked by blotch is peach {Frunus

pérsica). The disease has been found on an unidentified variety and on

Marigold in nature, and it has been transmitted experimentally to the varieties

Elberta, Rochester, Vedette, Golden Jubilee, and Peregrine.

To date, transmission experiments with plum, apricot, and cherry varieties

and cherry seedlings have given negative results except for a vague and doubtful blotching on ItaHan Prune. The species and varieties used in these experiments included domestica plum (P. domestica) varieties Italian Prune, German Prune, Reine Claude, and Lombard; Japanese plum (P. salicina) variety

Abundance; myrobalan plum (P. cerasifera) seedlings; apricot (P. armeniaca)

variety Niagara; sweet cherry (P. avium) varieties Black Tartarian and

Napoleon (Royal Ann) and seedhngs; sour cherry (P. cerastis) variety

Montmorency; and mahaleb cherry (P. mahaleb) seedHngs. Whether or not

plums and cherries can act as carriers of blotch has not yet been determined.

Symptoms

The symptoms of peach blotch are well-defined pale-green to yellow-green

variegations of the leaves (fig. 35). Up to the present no symptoms have

been observed on flowers, fruits, or twigs. The variegations may be numerous,

small, angular spots scattered over the leaf surface or less numerous, large,

irregular blotches. Sometimes there is a single chlorotic area arranged

symmetrically along the midrib and having its margins either well defined or

feathered out along the lateral veins. Some leaves are marked only by a

yellowing of the veins, and others may be symptomless. The patterns may

also be reversed, dark-green areas on a chlorotic background. The margins of

some leaves become scorched and soon drop off, leaving a ragged edge, or less

frequently large necrotic spots may develop. On some varieties, such as Elberta, and on some seedlings, most of the pattern types can be found (245),

The feathery-edge pattern predominates on Rochester leaves, while leaves of

Vedette show a few large blotches appearing in some seasons but not m

others. Golden Jubilee is usually symptomless, though in some years a few

early leaves may have a mild mosaic or a yellowing of veins. Some seedUngs

exhibit either faint symptoms or none.

Diagnostic or Unusual Characteristics

Peach blotch is unusual in its isolated occurrence in nature. It differs

93
94 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Figure 3 5.—Peach leaves affected with peach blotch.

from peach mottle in that it causes no symptoms in cherry and from peach

caUco (24) in that there is an absence of symptoms on twigs and fruits.

Transmission

Transmission has been effected only by budding and grafting. There is as

yet no evidence that this disease spreads in the orchard.

Incubation Period

Symptoms appear on trees in the spring after late-summer inoculation.

Control Measures

Selection of disease-free scion and stock material for propagation is recommended.

Remarks

It is still an open question whether diseases like peach blotch are the result

of sporadic infections involving préexistent viruses or originate within the

host as a result of alteration in some part of the host's cellular components.
WILLOW TWIG

By H. EARL THOMAS

Name of the Disease

The death and shedding of a majority of the lateral leaf buds on peach,

resulting in slender, pendulant twigs similar to those of certain willow species,

suggest the name 'Villow twig." A rough bark condition on some branches

of affected trees suggests that this disease may belong to the rough bark group.

Name of tlie Causal Virus

No Latin binomial has been applied to the causal virus.

Geographic Distribution

Willow twig is fairly common from Sutter County south to Merced in

central California and occurs less frequently in certain of the coastal counties

(231).

Economic Importance

Affected trees may live indefinitely, but their fruits are inferior in quality

and quantity, perhaps because of the reduced amount of foUage. The disease

is the cause of local losses. The chief threat is that it may be spread in

nursery stock by undiscerning propagators.

Host Range

The disease has been found to affect peach {Pnmus pérsica) varieties J. H.

Hale, Phillips, and Paloro, flowering peach, and nectarine (P. pérsica var.

nectarina) variety Quetta.

Symptoms

The principal feature of this disease is the dying and shedding of lateral leaf

and fruit buds during the winter and the resultant willowy growth and

sparse foliage {ii^, 36). On J. H. Hale peach, fruit buds are more persistent

than leaf buds, but if leaf buds are lost, the fruits on these spurs do not

mature properly. When a lateral bud grows as much as half an inch during

the season in which it is formed, it is likely to survive and produce a side

branch the following year. The main terminal bud of a branch usually survives but occasionally does not; in such a case progressive dieback results in

loss of the whole branch. Affected branches at 5 years of age may be no

thicker than a normal 1-year-old branch and are more flexible than a normal

branch of the same diameter. On affected trees the first leaves in spring tend

to be shorter in proportion to width than is normal for the variety.

On affected branches of Paloro, leaves tend to persist longer than on normal

ones, often to mid-December, and some have a yellow band around the edge

extending halfway to the midrib. Symptoms vary in severity on different

branches on the same tree.

Symptoms appear to be more pronounced on trees in the warmer parts of

the interior valleys. The effect of temperature is further supported by production of more pronounced symptoms on trees in the greenhouse than on trees

growing out of doors at Berkeley. Heavy applications of nitrogen have produced Httle effect on the symptoms picture. Spring pruning by cutting off

95
96 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

terminals of the current-season growth has not been effective in reducing the

symptoms on new growth.

Transmission and Incubation Period

Willow twig has been transmitted by grafting diseased scions onto nurserysize trees, but three or more years are necessary for characteristic symptoms

to develop. The rate of natural spread appears to be slow.

Figure 3 6.—Twigs of J. H. Hale peach affected with willow twig.
VIRUS DISEASES OF STONE FRUITS 97

Control Measures

The most efifective control measure is the use of healthy budwood sources

for propagation of nursery stock. Although the disease spreads slowly in the

orchard, there is little likelihood that it can be eradicated by diseased-tree

removal. The causal virus may be present in a tree for three or more years

before recognizable symptoms develop. Early-stage symptoms are not clearcut and may be confused with other conditions. The effects of insufíicient

chilhng are very similar to the symptoms of willow twig.

Remarks

The symptoms of willow twig on peach are similar in general to those of

the type of bud failure disease of almond that is reported to be nontransmissible.

Insufficient work has been done to determine the possibihty of any relationship

between these two diseases.
VIRUS DISEASES OF SWEET CHERRY

BUCKSKIN

By T. E. RAWLINS and H. EARL THOMAS

Names of the Disease

''Buckskin" is the name used for a destructive graft-transmissible virus

disease of sweet cherry in California (178). On peach, however, the disease

was called leaf-casting yellows (234) before it was proved that it was caused

by the buckskin virus. X-disease (226), western X-disease (265, 265a), and

yellow-red disease (103) have been used to designate a disease of peach and

chokecherry apparently caused by various strains of the buckskin virus. In

Oregon a disease of sweet cherry called albino cherry may be related to buckskin (266).

Name of the Causal Virus

Buckskin virus.

Geographic Distribution

Buckskin occurs naturally on sweet cherry in Contra Costa, Napa, Solano,

and Sonoma Counties and on peach in Butte, Contra Costa, Glenn, Merced,

Napa, Placer, Santa Clara, Solano, Sutter, and Tehama Counties, Calif. Various

strains of the virus are rather widely distributed in the United States, where

they cause disease on peach, cherry, or chokecherry.

Economic Importance

^ Because of the wide geographic distribution of the various strains of this

virus and the severe loss that they cause over wide areas, buckskin is probably

the most important virus disease of sweet cherry and among the most important virus diseases of peach. Numerous sweet cherry orchards in California

have been removed because of the disease.

Host Range and Varietal Susceptibility

Sweet cherry (Prunus avium) varieties Chapman, Black Tartarian, Bing,

Lambert, Napoleon (Royal Ann), Black Repubhcan, and Rockport are

susceptible to natural infection. Varieties that appear to show some resistance

to natural infection are Long Stem Bing and Coop's Special. Peach (P.

pérsica) varieties known to be susceptible to natural infection in California are

Early Crawford, Elberta, Fay Elberta, Lovell, Muir, Orange CHng, Phillips,

Shahl, Stuart, and Tuskena (Tuscan). Species that have been artificially

mfected are western chokecherry (P. virginiana var. demissa) ; sour cherry

(P. cerasus) varieties English Morello, Stockton Morello, and Early Richmond;

bitter cherry (P. emarginata) ; mahaleb cherry (P. mahaleb) ; almond (P.

amygdalns); and smoothpit peach (P. mira). Various hybrids (P. pérsica X

P. amygdalus, P. mira X P. pérsica, P. davidiana X P. amygdahs, and p!

amygdahis X P. fenzliana) also have been artificially infected."

In preliminary tests desert peach (P. andersonii), myrobalan plum (P.

cerasifera), David peach (P. davidiana), domestica plum (P. domestica)

variety French (Agen), fenzl almond (P. feitzliana), desert apricot (P.

fremonfii), hollyleaf cherry (P. ilicifolia), and klamath plum (P. suhcordata)

were nonsusceptible.

98
VIRUS DISEASES OF STONE FRUITS 99

Symptoms

Sweet cherry.—The symptoms of buckskin on sweet cherry on mazzard

rootstock (P. avmm) are very different from those on the same varieties on

mahaleb (P. mahaleb) rootstock (180). There are at least three strains

(Green Valley, Napa, and Palo Alto) and probably more of the buckskin

virus in Cahfornia alone. These strains can be distinguished by the characteristic symptoms they produce on sweet cherry on mazzard rootstock or

on peach, and therefore these hosts are most useful in the identification of the

disease. The symptoms on trees on mahaleb rootstock are so similar to those

produced as a result of girdling by gophers and various undetermined causes

as to make them of less diagnostic value. Infected trees on mazzard rootstock

ordinarily live for many years after infection, whereas those on mahaleb rootstock quickly show a marked decrease in vigor and often die within 1 or 2

years after infection.

The symptoms produced by the Green Valley strain on sweet cherry on

mazzard rootstock are usually localized at first, but after several years they

occur throughout the trees. Fruits fail to mature, remain small, have short

pedicels, hang on the tree after normal cherries have dropped, and tend toward

a conical form (pi. 14, A, B). Healthy fruits are shown in plate 14, C

and D. The blossom-end half of a fruit loses its natural luster and has the

characteristic buckskin appearance. Dark-colored fruits remain red when

they would normally be of a darker color; Kght-colored fruits remain yellowish

when they would normally have some red color at maturity. Affected trees

appear nearly normal during most of the growing season, but they may show

a faint bronzing of the leaves, retarded growth, and dieback after several

years of infection. During late summer or early fall the leaves have an

orange-red color along the basal portion of the midrib and in the adjacent

lamina (pi. 14, G). Infected trees can accordingly be most readily detected

at two periods in the season, namely, when normal fruits mature and in the

early fall, when leaves of infected trees have the orange-red color along the

base of the midribs.

The symptoms produced by the Napa strain on trees on mazzard rootstock

differ from those produced by the Green Valley strain in the following respects. On the affected portions of the trees the fruits fail to mature but

drop about ripening time. The fruits do not lose their luster or have the conical

form characteristic of infection with the Green Valley strain. The pedicels

are of normal length. The tree symptoms differ in that most spurs produce

terminal growth with short internodes. Such growths carry an excess number of small pale-green leaves and therefore have the rosetted appearance

shown in figure 37, C. The buds on affected portions have loose scales and

a resultant ragged appearance.

When sweet cherry trees are on mahaleb rootstock the symptoms produced

by the two strains of virus are very similar. The first symptom observed is a

general chlorosis of the tree followed by an upward rolling of the leaf edges.

The leaves begin dropping in midsummer, usually showing an orange-red

color along the midrib and lateral veins just before abscission. Much of the

mahaleb root system of an infected tree usually dies rather quickly after infection. If a tree survives into the second year, it usually has sparse foliage

and small pale-green leaves (fig. 37, A). A healthy branch is shown in

figure 37, B. Infected trees produce few fruits. These ripen and are approximately normal in appearance, but are soft and insipid. Infection with
100 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

figure 3 7.—A, Branch of Napoleon cherry on mahaleb rootstock, sho"wing the sparse

foliage characteristic of infection -with the Napa strain of buckskin virus; B,

unaffected Napoleon cherry branch; C, branch of Napoleon cherry on mazzard

rootstock, sho"wing the resetted foliage characteristic of infection -with the Napa

strain of buckskin virus.

the Napa strain occasionally causes the fruits on certain small branches to

remain small, immature, and green. These branches usually die before the

end of summer. June buds taken from these branches produce infection

when used as inoculum.

Schneider (202) found that there are much injury and wound-gum accumulation in sieve tubes of infected trees on mahaleb rootstock. These are

most evident in the tissues near the union. The wound gum becomes red

when sections are treated with phloroglucinol and hydrochloric acid. The

same reaction occurs in the branches of infected peach trees.

Peach.—Peach trees infected with the Green Valley strain show the following symptoms on certain branches. Leaves are pale green to greenish yellow;

those on older portions of affected branches have upward-rolled edges and

are recurved toward the stem. On the more vigorous apical portions of

affected shoots the leaves ordinarily appear normal until May or June, when

few to many red or purplish blotches appear in the leaf blade. These

blotches soon become necrotic (pi. 14, F) and drop out, producing a ragged

appearance of the leaves. Leaves drop from such branches in early summer to

midsummer, in succession from the base of the shoot upward. The fruits on

affected branches shrivel and drop early. Ordinarily the symptoms are seen

first on one or more branches and gradually from year to year symptoms appear

on additional branches until most or all of them are affected. Affected limbs

often die back; when such branches are removed a tree may appear healthy for

a year or more before it again shows symptoms.
VIRUS DISEASES OF STONE FRUITS 101

On peach the Napa strain produces symptoms similar to those produced by

the Green Valley strain. The main difference appears to be that the symptoms

produced by the Napa strain are much milder and tend to disappear the second

year after infection.

A third strain in California, known as the Palo Alto strain (202), causes

continued slow growth of affected peach branches throughout the summer.

Such branches have very short internodes and leaves that are much smaller

than normal.

Sotùr cherry.—English Morello trees on mazzard rootstock when inoculated

with the Green Valley strain of the buckskin virus produced little terminal

growth. The fruits remained small, and they shriveled before ripening. Early

Richmond trees on mahaleb rootstock showed a reddening of the leaves in

June, but the green color persisted in a narrow band around the margin of

the leaf. Such leaves dropped early.

Western chokecherry.—Western chokecherry infected with buckskin virus

shows a conspicuous carmine color on the lower leaves (pi. 14, Ê). This color

is more or less continuous along the edges of the leaves and between the main

lateral veins. The upper side of the midrib, the main lateral veins, and the

adjacent tissues tend to remain green.

Transmission and Natural Spread

Transmission has resulted from use of diseased scions or buds from certain

infected hosts. Best results are obtained by use of scions from infected Napoleon cherry trees growing on mazzard rootstock. Scions of Napoleon

and other varieties of sweet cherry tried on mahaleb rootstock do not provide

effective inoculum. Peach scions are also rather poor inoculum.

It is suspected that the virus is naturally transmitted by insects, but

numerous attempts to transmit it by such means have been unsuccessful.

Under natural conditions the Green Valley strain of the virus spreads

readily from cherry to adjacent peach orchards. Such spread has not been

observed in the case of the Napa strain of the virus in a number of localities

where peaches are adjacent to heavily infected cherries. One instance of

infection of peach in Napa Valley has been seen in a comparatively isolated

location, but the symptoms resembled more closely those of the Green Valley

disease. The peach may be readily infected with the Napa strain by grafting. It is therefore possible that the absence of natural spread of the Napa

strain from cherry to peach may be due to the absence of a suitable insect

vector in Napa Valley.

Incubation Period

Cherry trees inoculated by grafting in February may show symptoms by

the following June. On peach trees grown in the greenhouse the incubation

period may vary from two to many months.

Control Measures

Sweet cherry trees produced by top-working the desired variety on several

scaffold limbs of mahaleb seedUng rootstock have been commercially profitable

in the locahty where the Green Valley strain occurs. Where infection occurs

on individual arms the virus apparently fails to pass to other arms through the

mahaleb {179) and the diseased arms can be removed. Top-working has

therefore been the most satisfactory form of control for the Green Valley

strain of the virus on sweet cherry. Most sweet cherry varieties do not make

an entirely satisfactory union with mahaleb, and this incompatibility has
102 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

caused some difficulty. Bing makes a good union with mahaleb, and doubleworking may therefore prove to be a solution for this difficulty.

A satisfactory control for the Napa strain on sweet cherry has not been

worked out. In several States removal of infected chokecherry has been

recommended as a control measure for X-disease (103, 226).
ALBINO

By S. M. ZELLER, C B. CORDY, and J. A. MILBRATH

Name of the Causal Virus

Albino virus.

Geographic Distribution

The disease was first discovered in Ashland, Oreg., in June 1937 (266),

The local spread of albino has been very rapid, but the known distribution is

limited to the Rogue River Valley in southern Oregon.

Economic Importance

Albino is of great economic importance because it spreads rapidly and kills

affected trees. It has already eliminated several small orchards in the district

where it was first observed and will eventually eliminate commercial cherry

production in the Rogue River Valley. In one orchard without previous

infections, 38 percent of the trees were diseased in the first year of infection

and the following year over 90 percent were infected (67). Should this

disease become generally distributed the losses would be great.

Host Range and Varietal Susceptibility

The disease affects sweet cherry (Primus avmm) on mahaleb (P. mahaleb)

or mazzard (P. avmm) rootstocks. Albino has been found on Bing, Black

RepubHcan, Lambert, Black Tartarian, and Napoleon (Royal Ann) varieties

in orchards. The Bing, Napoleon, and Black Republican varieties are all

severely affected. Napoleon is possibly the most severely affected and most

rapidly killed of these three varieties. The Lambert variety appears able to

endure the disease longer than other sweet cherry varieties so far found

affected with albino, but it gradually succumbs to the disease. Black Tartarian shows considerable resistance. Montmorency sour cherry (P. cerasus)

has been experimentally infected.

Symptoms

All varieties of sweet cherry affected with albino show approximately the

same symptoms. Lambert, however, may be severely affected without showmg the typical fruit symptoms. In orchards the disease kills Bing and Napoleon varieties more quickly than others. All or any portion of the tree may

be affected with dieback, a usual symptom on diseased branches, beginning in

early spring as soon as leaves appear. As early as June leaves become uniformly

golden bronze green to olive brown, and the margins roll upward (pi. Í5, B,

C). Occasionally leaves about to be shed become bright yellow to orange, with

some pinkish tints, especially in a pinnate pattern along the midrib and

lateral veins at the base. In late summer new growth of small, green, rosetted

leaves is produced from terminal buds (pL 15, C). This character is general

on moderately diseased trees, and occasionally it is the first symptom observed

on otherwise vigorous trees. Fruits remain small and immature, even those of

dark-red-fruited varieties turning white (pL H, D-F). A heavy drop may

occur before harvesttime, but some of these small white fruits remain attached

long after normal fruits have dropped.

In the experimental nursery certain varieties infected by inoculation reacted differently from the way they did in the orchard. (See Transmission.)

103
104 HANDBOOK 10, U. S, DEPARTMENT OF AGRICULTURE

Transmission

Nursery trees of Bing, Napoleon, Lambert, Black Republican, and Centennial sweet cherries and Montmorency sour cherry on mahaleb and mazzard

rootstocks in separate series were infected with albino virus by inoculation in

the fall with buds from diseased shoots or by grafting with spurs which had

borne albino fruits. In the same experiment infection was obtained on Black

Tartarian trees growing on mahaleb rootstock.

When the trees were on mahaleb rootstock, all varieties except Black

Tartarian and Montmorency were killed by albino during the summer after

inoculation (pi. 16, A). In contrast, when the trees were on mazzard rootstock, most of them showed a severe shock reaction the first year, but only

a few died. Many of them were still alive 3 years after inoculation. At that

time the trees were dwarfed, the nodes were so shortened that the growth was

rosetted, and the fohage was light in color, often with a bronze cast. All

these trees produced albino fruits. Black Tartarian trees on mahaleb rootstock

reacted just as other varieties did on mazzard rootstock, thus indicating that

this variety has some resistance to albino.

Montmorency sour cherry on both rootstocks showed considerable resistance

to albino. All inoculated trees developed some symptoms of shock, but none

died. Those on mazzard rootstock had a somewhat more severe reaction than

those on mahaleb rootstock, possibly indicating that sour cherry on mahaleb

does not react in the same way as sweet varieties do. Three years after inoculation the trees had declined and died back somewhat. Occasionally fruits

on the most severely affected trees were small and light-colored, resembling

the albino fruits of sweet cherry varieties.

No fruit or leaf symptoms were produced on peach varieties inoculated with

buds from sweet cherry trees affected with albino in numerous tests. Indexing from the inoculated peach to sweet cherry indicated that peach is immune

from the albino virus. In a recent experiment alternate trees in a block of

90 young peach trees of 7 varieties were inoculated in the fall with buds from

sweet cherry trees affected with albino. The summer after inoculation all

uninoculated trees were normal green, but all inoculated ones had developed

a chlorosis similar to that induced by hme. Whether the reaction was caused by

albino virus or by ring spot virus as a contaminant in the inoculation is not

known.

Incubation Period

Sweet cherry trees bud-inoculated in late summer showed symptoms within

10 months.

Control Measures

No particular control measures have been outlined. Since albino is of

limited occurrence in a section where cherries are not of much commercial

importance, eradication should doubtless be attempted. Until such eradication is realized, measures should be taken to prevent the distribution of cherry

scion wood from the section where albino exists.

Remarks

Several of the symptoms described for albino are similar to those of buckskin {180, 257), Among these are the small whitish fruits, the pinkish and

orange tints at the base of leaves extending up the midvein and pinnately into

the lateral veins, and the soft buds and stimulated growth of small rosetted

green leaves late in the growing season. Certain characteristics, however,

distinguish albino from buckskin. The uniform golden-bronze greenness of
VIRUS DISEASES OF STONE FRUITS 105

the leaves, which is generally found associated with albino, is not described

as a symptom of buckskin.

In orchards sweet cherry varieties are killed by the albino virus (pi. 15, A),

but experimentally infected nursery trees reacted differently on mazzard rootstock from the way they did on mahaleb. Cherries on either rootstock are

naturally affected with Green Valley buckskin, according to Rawlins and

Parker (179), but they develop different symptoms; they wilt and die when

on mahaleb rootstock, whereas they produce small buckskin cherries but have

no leaf chlorosis during the growing season when on mazzard. "Western

X-disease (leaf-casting yellows) (234) of peach has been recovered from

cherry trees affected with Green Valley buckskin in California (ISO) and

from diseased cherry trees bearing little fruits in eastern Oregon; but, although

there are many peach trees interplanted with the cherries in the section where

albino occurs, no virus disease of peach has been observed there. Peach trees

inoculated with the albino virus have not developed any known virus disease.

Therefore, Green Valley buckskin, which seems to be caused by the virus that

causes western X-disease of peach, is distinct from albino.
MOTTLE LEAF

By H. R. MCLARTY, T. B. LOTT, J. A. MILBRATH,

E. L. REEVES, and S. M. ZELLER

Common Names of the Disease

The common name ^'cherry mottle leaf," which has come into general use

in the Paciñc Northwest, was first applied by Zeller (255) in 1934. Zeller

and Milbrath gave the name "severe mottle leaf to the rugose type and ''mild

mottle leaf" to the smooth type.

Names of the Causal Virus

The following names have been applied to the virus: ''Marmor cérame

Zeller and Evans" {259), "M. ceraú (Zeller and Evans) Holmes," "Prunus

virus 7 Zeller and Evans" {259), and "mottle leaf virus." Under the system of

naming proposed by Fawcett the name would be ''Pnmivir cerasi"

History and Geographic Distribution

Severe mottle leaf was first noticed in Oregon by Zeller {25 5) in 1920.

The virus nature of the disease was established in 193 5 by McLarty {146) and

Reeves {181). The disease occurs generally in the sweet-cherry-growing districts of Washington, Oregon, and Idaho and of British Columbia, Canada,

and has been observed in CaUfornia, Utah, and Montana. In Washington

severe mottle leaf is most prevalent in the foothill or canyon orchards where

the native wild bitter cherry {Prtmtis emarginata) may be found growing

nearby, and it occurs less frequently in open, wide valleys. In these latter

locations mild mottle leaf is the prevailing type.

Surveys conducted by Coe (66) showed that 1.4 percent of the total bearing sweet cherry trees in Washington and 3.5 percent of the symptom-expressing varieties were affected with mottle leaf. In Oregon mild mottle leaf is

prevalent in all districts where sweet cherries are grown, and severe mottle

leaf is found occasionally, as if introduced in grafting wood or nursery stock.

Economic Importance

Severe mottle leaf is the most important cherry disease in certain foothill

or canyon districts of north-central Washington. It is comparatively minor

elsewhere in Washington and in California. In Oregon certain forms of

mild mottle leaf constitute an important factor in cherry production. In British

Columbia the disease is considered of importance in the Kootenay area,

where the severe mottle leaf type predominates, and of minor importance in

the Okanagan, where mild mottle leaf is the prevailing type. In favorable

locations mottle leaf is considered to be a serious disease of sweet cherries.

Host Range and Varietal Susceptibility

Bing and Napoleon (Royal Ann) are the two varieties of sweet cherry

(P. avmm) most severely affected, but other varieties are susceptible and

suffer injury in varying degrees. Sour cherry (P. cerasiis) and duke cherry

(P. avmm X P. cerastis) are not immune, but they are practically symptomless carriers. Reeves {183) studied the reactions of various species and varieties

and reported the relative intensity of mottle leaf symptoms, shown in table 2.

106
VIRUS DISEASES OF STONE FRUITS 107

TABLE 2.-—Relative intensity of mottle leaf symptoms on species and

varieties of cherry

Pnmus Varietal or

common name

Leaf symptoms

species Mottling Rugosity

r Bing Pronounced

. . do

Severely puckered.

NaDoleon Do.

Waterhouse . . Moderate . . Puckered.

Centennial . ... do Do.

Black Tartarian

Early Purple

Slight, variable

... do

Moderately ruffled.

Do.

1 Governor Wood. ... do Do.

Black Republican

(Republican).

Lambert . .........

. . do Do.

slight, fugitive

... do

Lightly ruffled.

Deacon Do.

Parkhill seedlins ... do Do.

f Montmorency Occasional, slight . . .

... do

None.

P. cerasus Do.

L English Morello

r

May Duke . ......

None Do.

P. avmm X Occasional, slight ....

Very slight, fugitive. .

... do

Lightly ruffled.

Occasional light

ruffling.

Do.

Late Duke . •

McKee

P, mahaleb

P. emarginata . . .

Mahaleb cherry

Wild bitter cherry

Occasional, slight . . .

Medium, fugitive ....

Do.

Do.

Zeller and Milbrath found that the severity of reaction of sweet cherries to

both severe mottle leaf virus and strains of mild mottle leaf virus was in the

order: Bing, Napoleon, Black Republican, and Lambert. Some mazzard

seedlings showed violent reaction to severe mottle leaf virus. Peaches (P.

pérsica) apparently were symptomless carriers of both severe and mild mottle

leaf Virus, but this could not be definitely determined because of the interference of latent sweet cherry viruses. Black Repubhcan and Lambert varieties, when inoculated with mild strains of the mottle leaf virus, were essentially

symptomless except for an occasional chlorotic, elongated spot parallel with

the lateral veins.

Symptoms

The most distinctive symptoms of mottle leaf are expressed on the leaves of

affected trees. When severe mottle leaf occurs on the most susceptible varieties, Bing and Napoleon, there are an irregular, chlorotic mottling and a distortion early in the season and increased puckering of the leaves and variable

mottling as the season progresses {ñg. 3 8, A, B), Leaves are often reduced

in size and show some variable lacerations or shot holes following necrosis,

but there is no leaf casting {ñ.^. 38, C). When leaf symptoms are severe the

fruits may be abnormally small, later than normal in ripening, and insipid in

flavor, but not misshapen. The growth of the tree is stunted; the stunting

brings the spurs close together and gives the tree a rosetted appearance. On

other varieties the symptoms are generally similar in nature to those on Bing

and Napoleon, but they are less pronounced and vary widely from variety to
108 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

figure 3 8.—Cherry leaves affected with severe mottle leaf: A, Napoleon; B, Bing.

C, Branch of Bing cherry affected with severe mottle leaf, showing symptoms in

the new tip growth.
VIRUS DISEASES OF STONE FRUITS 109

Figure 39.—Cherry leaves affected -with severe mottle leaf: A, Black Republican;

B, Lambert.
lio HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

variety (fig. 39, A, B). Mild mottle leaf virus causes similar symptoms of

less intensity (fig. 40), and tree productivity is not materially affected (184).

The different strains appear to be stable, inducing their characteristic effects

through subsequent transfers without attenuation or increment of symptoms.

Figure 40.—Napoleon cherry leaves affected with mild mottle leaf.

Zeller and Milbrath found that inoculations with mild mottle leaf virus

caused considerable dwarfing of young Bing and Napoleon trees. In Oregon,

orchard trees infected by these mild strains showed loss of vitality and much

dieback. It was felt that some of the dieback might have been due to an

induced sensitivity brought about by drought, winter injury, or other factors.

Symptoms of both severe and mild mottle leaf are at least partially masked

by high temperatures. Masking is indicated by the occurrence of characteristic

symptoms on new growth in the spring or fall and the absence or suppression

of these symptoms on new growth in midsummer.
VIRUS DISEASES OF STONE FRUITS 111

Transmission and Incubation Period

Transmission is readily obtained through any tissue union that results from

budding or grafting. The natural vector of the virus is not known.

There is some evidence to indicate that the virus spreads from the wild

bitter cherry to nearby cherry orchards. Surveys showed that there was a

higher incidence of mottle leaf in orchards located close to native stands of

this cherry. Spread in an orchard varies widely in different localities and in

different years. Reeves (183) stated that in north-central Washington in

52 orchards in which at least 1 affected tree was known to be present the

spread over a 4-year period was considered serious in only 7 orchards. In 1

planting of 84 trees 6 showed mottle leaf in 193 5; 1 new infection occurred

in 1936, 0 in 1937, and 21 in 1938.

Zeller and Milbrath transmitted both severe and mild mottle leaf virus

from cherry to peach and back to cherry. In limited tests they showed that the

virus is not seed-borne.

In artificial transfers the period of incubation varies according to the stage

of seasonal development. Reeves (183) reported that in spring inoculations

in the field symptoms were obtained as early as 37 days after treatment,

whereas those made in midsummer and later failed to produce symptoms until

the following spring. In greenhouse tests symptoms were obtained after 14

days.

Control Measures

Control of mottle leaf in future orchards must be through the use of clean

nursery stock or grafting wood. For all propagation work scions should be

obtained only from trees that have been proved to be virus-free.

Since trees affected with this disease do not recover, diseased-tree removal

is recommended in established orchards when productiveness is affected. In

orchards adjacent to stands of wild bitter cherry it is recommended that

tolerant sweet cherries be used. It is not considered practical to eradicate the

wild bitter cherry.

Remarks

The name "mottle leaf" is used to designate a diseased condition caused by

several distinct but closely related virus strains. The symptoms they induce

in infected plants are classified generally into two groups, severe mottle leaf

and mild mottle leaf. All strains of the causal virus may be transmitted

without change in type of symptom expression.
RUSTY MOTTLE 22

By E. L. REEVES

Other Common Names of the Disease

Zeller and Milbrath (264) referred to rusty mottle as severe rusty mottle.

Names of the Causal Virus

Marmor nibiginosum Reeves (1S2) has been used. Under the system of

naming proposed by Fawcett the name would be ''Pnmivir nibiginosum"

History and Geographic Distribution

In 1940 rusty mottle was reported as a new virosis of cherry that had been

repeatedly transmitted during the previous S years by grafting or by some

adaptation of the grafting process (182). It was also referred to as a disease

sometimes confused with mottle leaf of cherries {183). In 1942 Zeller

(256) referred to rusty mottle in Oregon as a bronzed ring spot type of

disease differing from the type described in Washington. In 1947 Zeller and

Milbrath (264) further described the type occurring in Oregon as mild

rusty mottle, made comparative studies of it and the type described by Reeves

(182), and decided that the two types were distinct in several respects. In

1945 Richards and Rhoads (200) described a rusty mottle of the sweet cherry

in Utah, now referred to as necrotic rusty mottle (p. 120), which has some

symptoms closely resembling those of the disease that occurs in Washington

but which affects the tree more seriously. Later Reeves and Richards (189)

described certain differences between the types of rusty mottle in Utah and

Washington, but in the absence of comparative tests reached no positive

decision as to their relationship.

Reeves (184) stated in 1943 that ^'different strains of the virus may

be involved in the problem . . .," but during an orchard survey in Washington, reported by Coe (66), no distinction was made in reporting rusty

mottle as it was first described and the supposedly milder form of the disease.

It is now recognized that probably more than half of the rusty mottle reported

in the 1942 orchard survey (66) is the same as mild rusty mottle described

by Zeller and Milbrath (264). Also, during 1946 in one Washington orchard

a diseased cherry tree was observed with symptoms more closely resembling

those of necrotic rusty mottle in Utah than any disease previously observed

in Washington. Similar symptoms were observed on several trees in two

other orchards near Wenatchee, Wash., in 1949.

Rusty mottle has been found distributed in cherry orchards of Chalan,

Douglas, and Yakima Counties, Wash. In Idaho diseased cherry trees with

symptoms closely resembling those of rusty mottle have been observed, but

no positive statement can be made whether the disease is identical with rusty

mottle.

Economic Importance

Although rusty mottle appears to be somewhat localized in its occurrence

in Washington cherry orchards, it is of economic importance in the orchards

^^ The report given in this section is confined to the type of rusty mottle originally described by Reeves {1^2).

112
VIRUS DISEASES OF STONE FRUITS 113

where it is found. Orchard surveys in Washington, reported by Coe {66)y

showed that 59 out of 810 properties inspected in 3 counties had trees affected

with rusty mottle. While the average of infected trees in the 59 orchards was

only 2.9 percent, a few orchards had 19.4 to 34 percent of the trees affected.

However, as previously stated, in the survey reported by Coe (66) no distinction was made between rusty mottle and mild rusty mottle. How many

of the trees were actually affected with rusty mottle as described in this

section can only be estimated; possibly about 2 5 to 3 0 percent were so affected.

Host Range

In Washington all varieties of sweet cherry {'Prunus avium) commonly

grown in commercial orchards and mazzard (P. avium) seedlings have been

found affected or have been successfully inoculated by budding. Several

varieties of peach (P. pérsica) and sour cherry (P. cerasus) have been successfully inoculated by budding, but they have not been found naturally

infected.

Symptoms

Sweei cherry.—In Washington Reeves {^2, 183) reported that the first

foliage symptom appears 4 to 5 weeks after full bloom as a chlorotic mottling

of the older leaves. All the foliage soon becomes more or less affected, and

various percentages of the leaves develop late-season colors (bright yellow to

red) with islands of green {ñg. 41, B), Leaf casting of the brightly colored

foliage takes place largely during the 2 to 3 weeks prior to fruit harvest. The

mottling of the remaining foliage then becomes more pronounced and the

chlorotic spots and areas become yellowish brown; and a general rusty appearance of the foliage results. On trees affected for more than 2 years fruits

are often smaller than normal ones, retarded in maturity, and insipid in flavor,

but not misshapen {ñg. 41, C). The general effect of the disease on the fruits

is apparently dependent upon the severity of foliage symptoms and the percentage of leaves cast prior to harvest.

Peach.—Reeves observed foliage symptoms on several varieties of freestone

peach inoculated with buds from cherry trees affected with the type of rusty

mottle reported in Washington. Symptomatological patterns on peach leaves

are variable and striking in appearance. During late June and early July a

variable portion of the foliage turns partially greenish yellow, yellow, and

sometimes orange, and the chlorophyll degenerates so as to produce various

ring spots and patterns. Such affected leaves soon fall, and relatively few

leaves with distinctive recognizable symptoms remain on the tree. The period

during which recognizable foliage symptoms may be observed is variable, but

it may be as short as 12 to 15 days.

Transmission

Transmission has been easily effected by means of grafts or some adaptation

of the grafting process with tissues taken from either shoots or roots of a

diseased tree.

Incubation Period

Trees inoculated in late summer by budding exhibit symptoms the following year at the time when symptoms of the disease usually appear. Trees

inoculated during late March and early April by top or root grafting often

exhibit symptoms by mid-June; but sometimes recognizable symptoms do

not appear until the following year.

Control Measures

Diseased trees should be removed if they are affected so much that a
114 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

profitable crop is no longer being produced or whenever their presence is considered a menace to the healthy trees in the orchard. The careful selection of

propagation wood from nonaííected trees is especially recommended as a

preventive measure.

Figure 41.—A, Normal leaf of Bing cherry; B, comparable leaves affected with rusty

mottle, showing various patterns that develop on leaves that are cast prior to

harvesttime; C, branch from a Bing cherry tree affected with rusty mottle, 1 week

before harvesttime, showing that the fruits are not malformed but that the leaf

cast has been heavy.
VIRUS DISEASES OF STONE FRUITS 115

Remarks

While the leaf patterns as exhibited by the affected foliage (ñg. 41) are

variable, there is some resemblance between these symptoms and those exhibited by foliage of sweet cherry affected with each of at least three other

virus diseases: namely, mild rusty mottle (264), Lambert mottle {141), and

a rusty-mottle-like virus disease of the sweet cherry in Utah (189), now

referred to as necrotic rusty mottle. Under field conditions and at particular

periods during the growing season leaves could be found on trees affected with

any one of the four diseases that would exhibit symptoms common to the

other three. However, there are other diagnostic features of each of the four.

These are variable, and, of course, the intensity, extent, or severity of the leaf

patterns of each disease may also vary. This emphasizes the necessity of further

work in comparatively studying these four diseases and the impossibility of

diagnosing accurately any of the four from a few detached specimens or from

photographs of affected foliage.
MILD RUSTY MOTTLE

By S. M. ZELLER and J. A. MILBRATH

Name of the Causal Virus

Mild rusty mottle virus.

Geographic Distribution

Mild riisty mottle (264) occurs in some sections of Oregon, Washington,

and Idaho. In Oregon it has been observed throughout the Willamette Valley

and in Curry, Hood River, and Wasco Counties,

Economic Importance

Mild rusty mottle ranks first among the mottle-type virus diseases of sweet

cherry in Oregon. Surveys (256) showed that 20 percent of the trees in one

orchard at least 3 5 years old had mild rusty mottle and that in another orchard

about 2 5 years old 32 percent of the trees were affected. In some orchards

it was estimated that more than 5 0 percent of the trees were infected. On

the other hand, some of the oldest orchards have little or no mild rusty mottle.

Some young orchards are relatively free of it, but others, originating from

different nursery stock, have scattered trees apparently infected from the

start. Although trees affected with mild rusty mottle continue to produce

fruit for a number of years, the trees gradually decline and the loss from the

disease in northwestern sweet cherry orchards is undoubtedly of considerable

economic importance.

Host Range and Varietal Susceptibility

Mild rusty mottle seems to affect one variety of sweet cherry (Pruniis

avmm) about as much as another. In orchards it has been found affecting

trees of Bing, Black Republican, Black Tartarian, Lambert, and Napoleon

(Royal Ann) varieties. The causal virus has been obtained from Montmorency sour cherry (P. cerasus). A number of other species and varieties

of stone fruits have been found by inoculations to be susceptible. Peach (P,

pérsica) and Italian Prune (P. domestica) proved to be symptomless hosts

of the virus. Mahaleb cherry (P. mahaleb) seedlings, western chokecherry

(P. virginiana var. demissa)^ Indian plum (Osmaronia cerasiformis), and

oriental flowering cherry (P. sernilafa) varieties Amanogawa, Kwanzan,

Shirotae (Mount Fuji), Naden, and Shiro-fugen were inoculated vâth mild

rusty mottle virus, but slight if any symptoms were expressed. No return

inoculations have been made to sweet cherry from the plants just listed.

Symptoms

Sweet cherry.—All varieties of sweet cherry aft'ected with mild rusty mottle

show approximately the same symptoms. Even from a distance afifected trees

stand out because of their general yellowish-green color. The foliage takes on

a rusty or bronzed appearance by late June or early July. Older infected trees

often show considerable dieback and unthriftiness, probably due to the combined efifects of the disease and unfavorable factors such as drought and low

temperatures. At any rate affected trees seem to decHne more rapidly than

healthy ones. Decline is indicated by poorer terminal growth, poorer set on

fruiting spurs, and other symptoms, although it is much slow-er than that

brought about by severe rusty mottle (rusty mottle, p. 112) (182),

116
VIRUS DISEASES OF STONE FRUITS 117

During the first season of infection the disease may be found on only a

single branch, but by the next season it may have spread to the whole tree.

There are no particular leaf symptoms early in the spring. Usually the first

mottling appears in May or June on leaves which have attained a certain

maturity, some distance from the growing tips. There are no symptoms on

the terminal growth throughout the season. The mottling starts as yellowish

or light-green areas in the leaves. These areas are of various shapes (fig. 42).

Figure 42.—Bing cherry leaves affected "with mild rusty mottle.

In individual areas the centers are lighter yellow than the margins, which

gradually become bronzed or reddish. This bronzing or rustiness shows first

on the upper leaf surface, but gradually the leaf becomes rusty below. Bronzing borders the areas whatever their shape or size. At times the bronzing or

rustiness is in the form of tiny stipples. The stippling may be on the veins

or very close to them before it shows in the interveinal tissue, and it usually

starts at the base of the leaf blade. If the rustiness forms a line pattern or

rings, it is usually feathered out on at least one side. At times the older leaves

or those that are shaded, in the center of the tree, may become chlorotic and

develop a bright-yellow or whitish mottle. Such leaves are shed early, but

such shedding does not make the tree look generally defoliated. In unusual

cases certain trees may shed many relatively greenish, mottled leaves even

before harvesttime, but the next year the same trees may have no such leaf

cast during the summer.

Fruits of infected trees are somewhat retarded in ripening. Fruits of the

Napoleon variety are inclined to be clear yellow and usually without the red

cheeks of healthy fruits.

Sour cherry.—Montmorency sour cherry trees from which mild rusty

mottle was recovered had considerable dieback and a peculiar leaf symptom,

891793 0—51—10
118 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

neither of which has been definitely proved to be expressions of this particular

disease. The leaves had a mild mottle, and they were much smaller than

normal. The undersurface of the leaves was mottled with a rusty coloration

brought about by necrosis of the lower epidermis in certain areas; the rustiness may be limited to one side of the leaf or to the central area or may occur

along the veins. A close examination of the rustiness with a lens shows that

it starts with a reddish necrosis along the velnlets. This spreads along these

veins until the whole spot has a reddish-mottled appearance to the naked eye.

At this stage the upper surface appears mottled, and the older chlorotic spots

begin to show necrosis above.

Transmission

Mild rusty mottle is perhaps as easily transmitted as any other woody-plant

virosis. Whenever sweet cherry was inoculated by budding with infected

sweet cherry tissue, transmission was successful with or without apparent

organic union of the two tissues. Inoculum from the following districts was

compared on sweet cherry: Benton, Hood River, Lane, Multnomah, Polk,

Wasco, and Washington Counties, Oreg., and Benton and Yakima Counties,

Wash.

The disease was transmitted to the following varieties of sweet cherry:

Bing, Black Republican, Deacon, Golden, Lambert, Napoleon, and Schmidt;

to mazzard seedlings; and to Montmorency sour cherry. The following species

or varieties showed slight if any symptoms: Mahaleb cherry seedlings; oriental

flowering cherry varieties Amanogawa, Shirotae, and Shiro-fugen; western

chokecherry; and Indian plum. Occasionally Kwanzan and Naden varieties

showed slight leaf symptoms.

Many peach, plum, and prune varieties were inoculated, but none showed

leaf symptoms. Peach and Italian Prune were proved by retiirn inoculation to

sweet cherry to be symptomless hosts of mild rusty mottle virus.

Incubation Period

Trees inoculated by budding or patch grafting in late summer showed

symptoms in 10 to 12 months.

Control Measures

New orchards should be established with clean nursery stock. In established

orchards where few trees are infected, the diseased trees should be removed.

If the removal of infected trees would too greatly deplete an established

orchard, it might be advisable to allow them to remain until unprofitable. If

a thinning program is necessary in a too closely planted orchard, mapping of

the diseased trees should precede pulling and the pulling of trees should be so

arranged as to remove the greater number of diseased trees.

Remarks

Mild rusty mottle (264) is distinct from severe rusty mottle, which is

caused by Marmor rubigmomín Reeves and was described by Reeves in 1940

(182) and 1943 (184). They differ in severity of effect on the trees, in

symptom expression on leaves, fruits, and bark, and in the amount of leaf

cast.

Sweet cherry trees affected with mild rusty mottle do not decline so rapidly

as those affected with severe rusty mottle. The fruits of trees affected with

mild rusty mottle are almost normal in size and quality, whereas those of

trees of the same varieties affected with severe rusty mottle are reduced in

size and insipid. The superficial splitting of the bark on 1-year-old wood
VIRUS DISEASES OF STONE FRUITS 119

caused by severe rusty mottle has never been observed on trees affected with

mild rusty mottle.

Leaf casting of Bing cherry trees affected with severe rusty mottle is usually

sufficient to cause the trees to have a stripped, bare, or defoliated appearance

(184), Such severe leaf casting has never been observed in trees affected

with mild rusty mottle.

Severe necrosis of the chlorotic areas in leaves of sweet cherry affected with

severe rusty mottle is usually apparent by late spring or early summer; in

trees affected with mild rusty mottle bronzing occurs, but necrosis is seldom

if ever seen as a leaf symptom.

After about the first of June symptoms of severe rusty mottle show on

leaves almost to the tips of branches, while on trees affected with mild rusty

mottle there are no leaf symptoms for some distance back of the growing tips.

Certain plants, such as peach, western chokecherry, and some varieties of

oriental flowering cherry, inoculated with mild rusty mottle virus, develop

no particular leaf symptoms, whereas the same varieties and species inoculated

with severe rusty mottle virus show the rustiness and bronzing in the leaves

similar to those described on leaves of sweet cherry.
NECROTIC RUSTY MOTTLE

By B. L. RICHARDS and E. L. REEVES

Other Common Names of the Disease

Rusty mottle {195, 200); rusty-mottle-like disease (189).

Name of the Causal Virus

Necrotic rusty mottle virus.

History and Geographic Distribution

The virus nature of necrotic rusty mottle of sweet cherry was not established until 1944 (189^ 195, 200); however, the disease had been recognized

many years earlier as a destructive factor in Utah orchards and had been

referred to locally by such names as "cherry leaf spot," "cherry leaf drop," and

"cherry leaf rust." In 1945 the disease was discussed in publications entitled

"Rusty Mottle of the Sweet Cherry in Utah" (19 5, 200), because of certain

similarities of the disease in Utah to rusty mottle of sweet cherry in Washington described by Reeves (182) in 1940. In 1946 the disease in Utah was

described as a rusty-mottle-like disease of sweet cherry (189) in recognition

of the fact that the similarities of the diseases in the two States were not as

clear-cut as formerly assumed. Subsequent studies of the various types of

rusty mottle disease expressions throughout Utah and in the Northwestern States

indicate definitely that, even though the disease in Utah has many characteristics in common with the rusty mottle described by Reeves (182) and also

with the mild rusty mottle reported by Zeller and Milbrath (264) in Oregon,

there are certain critical symptomatological differences which justify considering the trouble in Utah a distinctively different disease. It is reported

here for the first time under the name "necrotic rusty mottle." So far as

known, necrotic rusty mottle of sweet cherry occurs only in Utah.

Economic Importance

Necrotic rusty mottle is a major problem in sweet cherry production in

Utah. In a preliminary survey during 1944, 2 0.9 percent, or 27, of the

129 orchard blocks visited in 4 counties showed the disease (200). In 10 of

the 27 affected orchards 10 percent or more of the trees were diseased. In

5 of these orchards 22 to 46 percent of the living trees were affected. Pronounced leaf necrosis, bud killing, devitalization, and frequent death of

affected trees emphasize the seriousness of the disease.

Host Range and Varietal Susceptibility

Necrotic rusty mottle occurs principally on Bing, Lambert, and Napoleon

(Royal Ann) varieties of sweet cherry (Pnmus avinvi). The disease has

been found occasionally on Windsor and once on an unidentified early blackfruited variety of sweet cherry. Black Tartarian is known to be a symptomless carrier of the necrotic rusty mottle virus. The disease has been transmitted to mazzard (P. avhun) seedlings.

Symptoms

Trees affected with the necrotic rusty mottle virus show a delayed development of leaves and blossoms in the spring (pi. 16, C). Leaves on diseased

trees appear healthy during the first 3 to 5 weeks after petal fall. After this

period brown necrotic spots of varying size, shape, and distribution develop

120
VIRUS DISEASES OF STONE FRUITS 121

rather abruptly in the more mature leaves throughout the tree (pi. 17, A).

The portion of the leaf blade that is necrotic is greater on some trees than on

others. In mazzard seedlings and in the Lambert variety the initial necrosis

may be so extensive that severe defoliation may result.

Two to three weeks after the onset of the initial symptoms many of the

remaining leaves become prematurely senescent (pi. 17, A) and fall. This

second partial defoliation reaches peak expression some 2 or 3 weeks before

harvest. It may cause losses of 2 5 to 85 percent of the remaining leaves on

the tree.

About the time the fruits ripen yellowish to rust-colored chlorotic areas

appear in the older surviving leaves. These areas may be generally distributed,

resembling closely the chlorotic area described for mild rusty mottle (264)

and for the type of rusty mottle described by Reeves (184). Late in the

season, usually after harvest, the necrotic areas in the remaining leaves frequently fall out, and produce a conspicuous shot-hole effect. These rusty

chlorotic areas, the brown necrotic spots, and the shot holes constitute the

most important diagnostic symptoms of the disease during the latter part

of the season. Except for a comparatively few necrotic spots and rustcolored areas, the apical leaves on branches and water sprouts (suckers)

seldom show any of the late-season symptoms.

Autumnal senescence of the leaves on diseased trees occurs 2 to 4 weeks

earlier than that of leaves on healthy trees. It is characterized by prominent

rings and line patterns of dark green on a background of yellow, brown, or

brilliant red (fig. 43).

As the disease develops part of the buds and leaf spurs are killed. This

killing results in bare, rangy branches with terminal tufts of fohage, as shown

in plate 16, B. In the more advanced stages of the disease, the older branches

Figure 43.—Late-fall, senescent leaves from Lambert cKerry tree inoculated with

necrotic rusty mottle virus, showing rings and line patterns.
122 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

of the tree are killed and numerous water sprouts may develop from the trunk

or from the lower portions of the main branches (pi. 16, B). On the

cortex of young branches of some cherry varieties there occur numerous

cankers, or bhsterlike lesions, which as growth continues cause pronounced

roughening of the bark. Frequently this feature is so prominent that it provides a very significant symptom of the disease.

Transmission

The virus of necrotic rusty mottle has been transmitted by budding with

equal facihty to mazzard seedhngs and Bing, Lambert, and Napoleon varieties

of sweet cherry. Transmissibihty by this method is high, approaching 100

percent. Peach (P. pérsica), western chokecherry (P. vhginiana var.

demissa), Itahan Prune (P. domestica), and certain varieties of sour cherry

(P. cerasiLs) failed to produce visible symptoms when grafted with buds from

diseased sweet cherry trees.

Incubation Period

Trees inoculated in late August and early September exhibit symptoms the

following spring.

Control Measures

Diseased nursery stock provides the most common means of distribution of

necrotic rusty mottle, but there is some evidence of natural spread in orchards.

The use of virus-free budwood, both for propagation and for estabhshing pollinizers in orchards, offers the most effective method of control. Late-season

inspection and roguing of nursery stock just before leaf fall or before frost in

the fall may prove to be an additional safeguard in preventing the distribution

of the disease in nursery stock.
Agriculture Handbook 10, U. S. Department of Agriculture PLATE 15

^:

A, Dying albino-affected sweet cherry tree, contrasting with nearby normal trees. B, Branch of albino-affected

sweet cherry tree, showing late-summer symptoms. C, Terminal from a similar tree, showing small green

and older greenish-bronze leaves. D-F, Sweet cherry fruits affected with albino, contrasting with normal

fruits: D, Lambert; £, Napoleon; F, Bing.
Agriculture Handbook 10. U. S. Department of Agricukure PUATE 16

A, Bing cherry trees on iiialuleb rootstock, showing dying ol alternate trees, whieh were inoculated with albino

virus the previous fall; B, 14-ycar-old Lambert cherry tree showing bare, rangy limbs and tufted terminals

characteristic of advanced stage of necrotic rusty mottle; C, young Lambert tree inoculated with buds from tree

in B. showing retarded leañng and blossoming.
Agriculture Handbook 10. U. S. Department of Agriculture

rPLATE 17

A,

O

Lambert chcrrv leaves affected with necrotic rusty mottle,

ééé

showing early stage (left) and senescent stage (right);

B, Lambert cherry leaves affected with Lambert mottle, showing early stage (left) and senescent stage (right);

C, shoot from Lambert cherry tree affected with an apparently virulent form of Lambert mottle; D, Lambert

cherry fruits affected with little cherry, showing gradient in size as contrasted with normal fruit (left).
Atïricuhurc Handbook 10. U. S. Department of Agriculture PLATE 18

A, Bing cherry normal fruits (left) and spur from tree affected with small bitter cherry, showing two normal fruits

and five affected ones; B, Italian Prune leaves arranged to show a gradient ot Italian Prune leaf spot symptoms,

in contrast with normal leaf (upper left).
Agriculture Handbook 10. U. S. Department of Agriculture PLATE 19

Top: Bing cherry leaves and fruits affected with twisted leaf. Bottom: Bing leaf and fruits

affected with sweet cherry deep suture, in contrast with one normal fruit at left.
Agriculture Handbook 10. U. S. Department of Agriculture PLATE 20

A-C, Sour cherry yellows on Montmorency cherry: A, Leaf showing irregular pale-green or yellowish mottling;

B, leaf showing retention of green along main veins; C, branch showing willowv type of growth. D, Comparable normal branch with fruit spurs.
Agriculture Handbook 10, U. 5. Department of Agriculture PLATE 21

A. Montmorency cherry leaves showing symptoms o( green ring mottle, B, Montmorency cherry fruits affected

with pinli fruit, in contrast with normal fruits.
Agriculture Handbook 10. U. S. Department of Agriculture PLATE 22

Wenatchee Moorpark apricot showing symptoms of ring pox on

the fruit.
LAMBERT MOTTLE

By T. B. LoTT

Name of the Causal Virus

Lambert mottle virus.

Geographic Distribution

Scattered affected sweet cherry trees occur in various parts of the Okanagan

Valley, British Columbia, Canada. The disease {141) has not been observed

in the Kootenay area of British Columbia, but was transmitted by Napoleon

(Royal Ann) cherry budwood obtained in that area.

Economic Importance

In most orchards the percentage of affected trees is low, though individual

trees may be seriously affected.

Host Range and Varietal Susceptibility

Sweet cherry (Primus avium) variety Lambert is affected, and symptoms

develop on it. The Bing variety is infected, but there is little or no symptom

expression. The Napoleon variety is probably a symptomless carrier.

Symptoms

The terminal shoots of Lambert trees on which the disease is well established

appear normal in the early spring; but as the season advances, all the buds on

the upper portion of many of these shoots either fail to open or swell and

figure 44.—A, Shoots of Lambert cherry affected with Lambert mottle, showing

death of upper buds and delayed and irregular development of flowers; B, comparable healthy shoot.

123
124 HANDBOOK 10, ü. S. DEPARTMENT OF AGRICULTURE

ultimately die (fig. 44). The development of the other leaf buds and of the

flower buds is both late and irregular. The one symptom which can be

observed at all times is the form of branching that results from the production of new shoots part way down the previous season's growth.

In late spring the foliage appears slightly thin, but individual leaves are

normal in appearance and most of them are full-sized. In early June a yellowish interveinal mottle begins to appear on the older leaves (pi. 17, B),

This is soon followed by numerous small spots of a purplish or chocolate color,

which later becomes brownish. These spots form lines alongside the veins

and also irregular lines and rings or partial rings without relation to the veins.

The lines of minute purplish spots are usually surrounded by a poorly defined

greenish-yellow border. In some leaves a similar greenish-yellow pattern

occurs without any purple spots.

In addition to these symptoms, and occurring without apparent relation

to them, there are areas of the leaf up to 3 cm. in length which become brown

and torn, but do not usually separate cleanly at the margin. Typically these

spots are irregular in outline, but sometimes they extend as a narrow line along

a vein. The brown areas occur on any part of the leaf blade except the midrib.

In midsummer the normal green of the older aflfected leaves changes to

yellow and the greenish-yellow pattern becomes slightly more green. At this

time defoliation of these leaves commences. The amount of defoliation varies

from year to year. Half of the leaves may fall prematurely.

Diseased trees set only a light crop, and sometimes many of the fruits do not

reach maturity. In some cases fruits of normal size and color have abnormally

short and curved pedicels. On some trees nearly all the fruits arise from single

buds on the lower part of the 1-year-old wood or a few surviving spurs on

the outer part of the 2-year-old wood. The number of fruit spurs may be

very greatly reduced.

The disease becomes progressively more serious for several years, and twigs

and larger branches die. Trees affected when young may die, but in older trees

the disease appears to become stabilized.

Diagnostic or Unusual Characteristics

The type of branching that results from the death of successive terminal

buds and the subsequent growth from lateral buds is characteristic.

Transmission

The disease is transmitted without fail to Lambert trees by budding or

grafting when the diseased inoculum makes union. It has also been transmitted by cambium scrapings placed under the barkr'^

Incubation Period

Leaf symptoms appear the first year after bud inoculation. Twig symptoms

do not appear until the second or third year.

Control Measures

Since Lambert mottle does not appear to spread rapidly in the orchard, it

is likely that it can be eliminated by removal of affected trees. Care should

be taken to use healthy budwood of all varieties for production of nursery

stock.

Remarks

In recent years a disease which may be caused by a virulent and quickacting strain of Lambert mottle virus has been observed in several places in

^* McLarty, H. R. Unpublished data.
VIRUS DISEASES OF STONE FRUITS 125

the Okanagan Valley and also in one orchard in the Kootenay area. No

transmission results are available. Trees aifected with this disease have leaf

markings similar to those caused by Lambert mottle. Leaf burning commences

at the tip and margins and may affect most of the blade (pi. 17, C). Extensive twig, branch, and limb killing occurs, and within a few years a tree is dead

except for a few scattered twigs and water sprouts which arise from the bases

of the limbs. In one 5-acre orchard nearly all the trees of the Lambert variety

were rendered worthless in about 10 years, but trees of several other varieties

showed no visible effect.

Symptoms of the above-mentioned disease closely resemble those of a disease

in Utah {1S9) now referred to as necrotic rusty mottle, according to Reeves.^^

Reeves reported observing similar symptoms on sweet cherry trees in three

orchards near Wenatchee, Wash. He indicated that the disease in Washington

and that in the Kelowna district of the Okanagan Valley are similar in their

effect on the tree, particularly in regard to the necrotic leaf areas and general

foliage symptoms; the extensive twig, branch, and limb killing; and the roughened bark that develops on many branches.

Reeves, E. L. Correspondence.
LITTLE CHERRY

By W, R. FOSTER, T. B. LOTT, and M. F. WELSH

Name of the Causal Virus

Little cherry virus.

Geographic Distribution '^^

Little cherry was first observed in 193 3 in a single orchard near Nelson,

British Columbia, Canada. It is now widely distributed in the scattered cherry

plantings in the mountainous southeastern part of the Province, along Arrow

Lakes and to the east of them. It has not yet been found in the Okanagan

Valley, where the main cherry plantings occur. A httle cherry disease has also

been reported in Washington (185), Idaho (168), Oregon (265), and Utah

(198), but its relationship to the one in British Columbia is not known.

Economic Importance and Natural Spread

Little cherry is the most important virus disease of sweet cherry in British

Columbia, because it reduces the vakie of the crop and its natural spread is

extraordinarily rapid. When the disease becomes established some cherries are

unmarketable. The majority can be processed into crystahzed fruit, which is

likely to be a somewhat inferior product. Some cherries can be marketed as

fresh fruit, but they lack the flavor, sweetness, and attractive appearance of

normal cherries.

The rate of natural spread of Kttle cherry is phenomenal. Usually all the

trees in an orchard are affected 2 or 3 years after the disease is first observed.

Information received from several sources (69) indicates that the disease first

appeared in 1 orchard in 193 3. In 1934, 3 nearby orchards were affected.

By 1940 the disease had spread in an area about 20 miles in diameter. In 1947

it was found in all the fruit-growing districts of the Kootenays, an area about

a hundred miles in diameter. This rapid spread took place in spite of many

natural barriers such as high mountains and large lakes and often considerable

distances between orchards, in one case about 3 0 miles. Few of the 30,000

cherry trees in the widely scattered orchards of the Kootenays are still healthy.

No little cherry was detected in 1947, 1948, and 1949 in an annual inspection

of the 68,000 cherry trees in the Okanagan Valley, just over a hundred miles

west of the original infection.

Host Range and Varietal Susceptibility

Sweet cherry {'Pninus avimn) varieties Bing, Black Tartarian, Deacon,

Lambert, Napoleon (Royal Ann), Black Republican, and Windsor are susceptible. Lambert and Black Republican are the most severely affected; Bing,

Black Tartarian, Deacon, and Napoleon are moderately affected. Sour cherry

(P. cerasiis) has not been included in transmission tests but has been observed

showing symptoms similar to those on sweet cherry. Other Vrnmis species

are not known to be susceptible and have not been observed with suspicious

symptoms.

-^^ In the present state of knowledge ît is impossible to know îiow many different diseases

or manifestations of the same disease are involved; therefore the description given here

applies to the disease as it occurs close to the first-observed infection near Nelson, British

Columbia.

126
VIRUS DISEASES OF STONE FRUITS 127

Symptoms

The known symptoms on sweet cherry are confined to the fruits. Diseased

trees set and retain large numbers of fruits. These apparently grow normally

until the end of the green growing stage. Development is variously retarded

from the time the fruit-ripening processes should commence. On diseased

trees many cherries are still readily visible above the leaves at picking time,

while on healthy trees the cherries are largely hidden under the leaves. Cherries

may hang on diseased trees for months without ripening fully. At picking

time many or all of the cherries on affected trees are half or less than half

normal size and retain the light red of immature cherries (17, D). Even those

cherries which are more nearly normal in size and color lack normal flavor and

sweetness and are usually dull in appearance, without normal gloss.

There is some difference in symptom expression on different varieties. From

year to year the severity of the disease varies a little in most varieties and

noticeably so in the Bing. The fruits of the Lambert variety in the second

and subsequent years of infection are rather uniformly affected, being about

half normal size, dull red at picking time, angular, and pointed, usually with

three flat sides tapering toward the distal end (fig. 45). On the Bing variety

B

Figure 45.—Lambert cKerry fruits affected with little cherry, showing a gradient in

size as contrasted with normal fruits at right: A, Side view; B, stylar-end view.

symptom expression is very variable. Usually the Bing is less affected than

other varieties, but sometimes Bing trees have very small cherries almost

lacking in color and dropping readily at about picking time. In mapped

orchards a number of Bing trees which had definite symptoms of little cherry
128 HANDBOOK xO, U. S. DEPARTMENT OF AGRICULTURE

for the first time in 1946 produced apparently normal fruits in 1947. There

is a tendency for affected cherries of the Bing variety to be somewhat lumpy

or irregular.

Symptoms of little cherry vary considerably in individual districts in the

Kootenay area and often even in individual orchards in a given district. In

certain orchards the effect of the disease on fruit size and color is very shght,

even on the Lambert variety.

Diagnostic or Unusual Characteristics

The fruits are small in spite of the good fohage and the apparently healthy

condition of the affected trees. Symptoms have been observed only on the

fruits. Diagnosis is most certain close to normal picking time. Lack of

flavor and sweetness even in fruits that appear normal is characteristic in all

varieties. Pointed cherries with three flat sides tapering toward the distal end

are typical in the Lambert variety. Natural spread is phenomenally rapid.

Transmission

Foster was the first to report definite transmission of little cherry in 1941,

on 2 Lambert trees which had been budded with diseased buds in 1940 {70,

73). Check trees remained healthy. Foster and Lott (73) reported that 4

Black Republican (Republican) trees and 16 Lambert trees were budded in

1943 with buds from diseased trees. In 1944 all the Black Republican trees

and 12 Lambert trees showed definite symptoms of little cherry, while 3 Lambert trees were highly suggestive of little cherry and 1 remained apparently

normal Check trees remained healthy. On most budded trees the part most

distant from inserted buds was apparently normal at the time of the first crop

after budding. Little cherry was evident throughout these trees the following

year.

Welsh attempted to obtain the little cherry virus from untreated trees of

Italian Prune (P. domestica). Vedette peach (P. pérsica), and two native

species (P. efnarginata var. mollis and P. virginiana var. demissa) by budding

to healthy cherry. No definite transmission has been obtained. Attempts to

transmit from cherry to these species and to Rochester peach and Moorpark

apricot (P. armeniaca) also have given negative results. P. eniargiîiafa var.

mollis budded in 1943 into a diseased Lambert tree produced apparently normal

leaves and fruits up to 1949 even though the Lambert tree on which it was

growing had been diseased for years.

Incubation Period

Trees bud-inoculated in the summer exhibit symptoms the following year.

Control Measures

The manner in which little cherry spreads is unknown. The rapidity of

spread in an orchard and from one orchard to another is so great that an insect

vector seems to be indicated. Prevention by tree reinoval is not certain to be

successful in the absence of vector control. Control is not being attempted

in the Kootenay area, where the disease is already prevalent. Control is being

attempted, however, in the Okanagan Valley, where the disease has not yet

been found. In 1947 there was begun a system under which the trees are

inspected twice and, if any trees having little cherry or suspected of having

it are found, they must be removed. The first inspection determines which

trees are normal and which require further checking. The second inspection

is made by those who are conversant with little cherry and other abnormalities

which might be confused with it.
VIRUS DISEASES OF STONE FRUITS 129

Remarks

No relationship is known to exist between little cherry and buckskin of

sweet cherry or western X-disease of peach. Furthermore, in the Kootenay

area of British Columbia the last has not been found in peach orchards, even

though the peaches are growing adjacent to cherry plantings which have had

little cherry for years. The little cherry that is present in the Kootenay area

is distinct from small bitter cherry, which occurs in the Okanagan Valley

always in proximity to peaches affected with western X-disease. A comparison

of the symptoms of little cherry with those of small bitter cherry is given on

page 130. The troubles known as western X little cherry in Washington,

Idaho, Oregon, and Utah resemble in their fruit symptomatology the little

cherry of the Kootenay area. However, no relationship with the Kootenay

little cherry has been established.

The seriousness of little cherry is due to the severe reduction in quantity and

quality of the fruit together with its unusually rapid natural spread. Experimental work has been rendered difficult by the inability of the investigators

to detect the disease other than in the fruit.

891793°—51—12
SMALL BITTER CHERRY

By T. B. LoTT

History and Geographic Distribution

Small bitter cherry has been present to a small extent in the southern part

of the Okanagan Valley, British Columbia, Canada, since 1940 and probably

somewhat longer.

Economic Importance

The effect of small bitter cherry is serious on some individual trees, but the

disease is of negligible importance in the Okanagan Valley.

Host Range

Small bitter cherry was observed on only the Bing variety of sweet cherry

(Pnimcs av'mm) before 1947. Three trees of the Lambert variety with symptoms apparently identical with those on Bing have now been found. Symptoms

have not been observed on any other variety, and symptomless carriers are not

known.

Symptoms

Small bitter cherry can be diagnosed most easily about normal picking time.

Earlier diagnosis is not possible, and after picking time diagnosis becomes

increasingly unreliable. Affected trees set about the usual number of cherries.

These are of two kinds with few intergrades. Small cherries may be few, or

they may constitute more than half the crop. Usually normal and small

cherries occur together, but on some branches all the cherries may be normal

and on others all may be small. It is common for only a small portion of a

large tree to bear affected fruit. There may be little or no evidence of increased distribution of the disease in an affected tree for as long as 4 years.

On the other hand, extensive increase in distribution may occur one year in

a tree in which there was no increase in the preceding year.

On affected trees of the Bing variety the normal-appearing cherries are

normal in size, shape, color, taste, and date of maturity. Most of the affected

cherries are less than half normal size and are more oval than normal ones

(pi. 18, A). At picking time they are bright red like immature cherries and

somewhat bitter, with an objectionable flavor reminiscent of the smell of stagnant ditch water. They may hang on the tree for a month or more without

ripening. After normal picking time they lose their bitterness and may taste

somewhat fermented. On some trees the smallest fruits are pink or almost

white and much underdeveloped at picking time.

Only three trees of the Lambert variety affected with small bitter cherry

have been observed. The symptoms on the Lambert variety appear to be

essentially the same as those on the Bing variety.

Diagnostic or Unusual Characteristics

Optimum conditions for diagnosis occur only within a few days of normal

picking time. The main diagnostic problem is differentiation between small

bitter cherry {142) and little cherry {7}), so that little cherry can be recognized if it appears in the Okanagan Valley.

Trees of the Bing variety when affected with small bitter cherry produce

fruits of two distinct types, some normal and others uniformly small, oval, and

130
VIRUS DISEASES OF STONE FRUITS 131

positively objectionable in flavor. Comparatively few fruits are either intermediate in size or exceedingly small. Trees of the Bing variety when affected

with little cherry produce cherries with a more even gradient from the best

to the worst. The best cherries are lacking in flavor and sweetness, and the

worst are small, irregular in shape, and lacking in flavor and sweetness, but not

positively objectionable in taste. Differentiation of these diseases is difficult

and sometimes uncertain on trees of the Bing variety.

Differentiation of these diseases appears to be less difficult on trees of the

Lambert variety. On Lambert trees affected with small bitter cherry, fruits

are of two types: normal; and uniformly small, oval, light in color, somewhat bitter, and positively objectionable in taste. Lambert trees experimentally

infected with the little cherry virus produced cherries that were uniformly

undersized, flat-sided, triangular in outline when viewed from the distal end,

dull in appearance, and lacking in flavor and sweetness, but not positively

objectionable in taste.

Other differences between the diseases are that little cherry virus is easily

transmitted and spreads rapidly within a tree whereas small bitter cherry virus

moves slowly through a tree and the incubation period is long.

Transmission

Transmission of small bitter cherry has been obtained in only one tree,

though eight trees were inoculated in 1941 and two in 1944. All these trees

fruited after inoculation, and some are still under observation. Transmission

was first obtained in 1949 in a tree that was inoculated in 1941. On this tree

two branches have grown from scions from a diseased tree, and the third

branch is part of the original inoculated tree. In 1947, 1948, and 1949 small

bitter cherry was definitely present on the larger branch resulting from on^

of the inserted scions. Small cherries were few and scattered, and most of

the cherries were normal. The smaller branch resulting from the other inserted

scion has consistently produced only normal cherries. In 1949 small bitter

cherry first became evident on the inoculated tree below the graft union, but

most of the original inoculated tree continued to produce only normal cherries.

Control Measures

The removal of infected trees is recommended. Material for propagation

purposes should originate from mature disease-free trees.

Remarks

Small bitter cherry has been found only in places where the western Xdisease is fairly common on peach, but limited experimental work has produced

no evidence of connection between the two diseases {142a).
RASP LEAF

By E. 'W. BoDiNE, EARLE C. BLODGETT, and T. B. LOTT

Other Common Names of the Disease

Rasp leaf has been called leaf enation, ruffled leaf, and cockscomb.

Name of the Causal Virus

Rasp leaf virus.

History and Geographic Distribution

Rasp leaf was first observed in Colorado in 193 5 by Bodine and Newton

(39), and evidence of its virus nature was reported in 1942. Lott and

McLarty (96) observed what is apparently the same disease in British

Columbia, Canada, transmitted it, and called it leaf enation. Blodgett (23)

reported its occurrence in Idaho and demonstrated its transmissibility. Reeves

(184) in 1943 stated that rasp leaf had been observed in Washington for several years although not previously reported. Rasp leaf was reported to be

present in Montana, Utah, and California (184).

Economic Importance

Observations in 1940 and 1941 indicated a rather rapid spread of the

disease within orchards in Delta County, Colo., and many severely affected

trees were found. In other districts where rasp leaf has been reported there is

no evidence of rapid spread, and therefore in such districts it may be considered

of minor importance. However, even in such districts (23, 184) individual

trees that are severely affected are markedly reduced in vigor.

Host Range and Varietal Susceptibility

So far rasp leaf has been reported on Bing, Black Tartarian, Lambert, and

Napoleon (Royal Ann) varieties of sweet cherry (Prumi^s avinm), on mazzard

(P. avmm) seedlings, and on Montmorency sour cherry (P. cerastes). The

Napoleon variety appears to be the most severely affected. On some of the

other varieties, and on mazzard trees especially, a milder manifestation of the

disease is frequently encountered.

Symptoms

The most characteristic symptom of rasp leaf is the production of abnormal

outgrowths on the lower surfaces of the leaves. These outgrowths (fig. 46)

vary from elongated protuberances to leaflike growths. On a given leaf the

growths usually occur between the veins and radiate from the midrib toward

the margin of the leaf blade. On the upper surface of a diseased leaf there are

depressed, roughened areas lighter in color than the normal green of the leaf.

Since the majority of the growths on the lower surface of affected leaves resemble the teeth of a coarse rasp, the name '*rasp leaf" was given to the disease.

Severely affected leaves are small, narrow, and markedly distorted. The leaf

blade frequently has a tendency to fold in upon itself. Trees may be completely or partially affected; it is not uncommon to find an uneven expression

of symptoms on a branch or a tree. Damage to diseased trees consists of

retardation in growth and the consequent reduction in the size of the crop.

Transmission

Transmission has been effected only through graft and bud inoculations.

Trees inoculated in the fall may show symptoms during the following growing

132
VIRUS DISEASES OF STONE FRUITS 133

figure 46,—Napoleon cherry leaves affected with rasp leaf, showing enations and

distortions.

season, but the virus appears to be limited to parenchyma tissue in that it

moves only a few inches from the inoculation point.

Incubation Period

The incubation period after inoculation may range from 9 months to ¿

years.

Control Measures

Since the productiveness of severely affected trees is markedly reduced, it

is recommended that such trees be removed. Furthermore, since the rasp leaf

virus is transmitted by bud and graft inoculations, extreme care should be

taken to obtain virus-free budwood for propagating nursery stock.

Remarks

Reeves (ÍS4) stated that it is not unusual to find casual leaf enations on

cherry leaves scattered throughout healthy trees. This is true particularly of

young trees and to some extent of older ones. The casual enations are not
134 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

readily noticed unless the foliage is closely examined, whereas the leaf symptoms of rasp leaf are usually very striking in appearance. So far as known,

these casual leaf enations are not of virus nature and therefore should not be

confused with rasp leaf.
TWISTED LEAF

By T. B. LoTT and E. L. REEVES

Name of the Causal Virus

Twisted leaf virus.

Geographic Distribution

Twisted leaf occurs in the Okanagan Valley, British Columbia, Canada, and

Chelan and Yakima Counties, Wash. A mild form of the disease, difficult to

identify with certainty, probably occurs occasionally in Idaho and may occur

in Oregon.

Economic Importance

Though twisted leaf does not have a wide distribution, it has caused considerable losses in a few orchards. According to surveys in Washington, reported by Coe (66), 147 infected trees out of a total of 199 were found in 1

orchard. However, in this orchard infection was largely due to the operations

of the orchardist, who followed the practice of budding in pollinizer varieties.

One of the pollinizers so employed was a mazzard seedhng that exhibited only

very meager symptoms and until indexed on Bing cherry could not be positively identified as affected with twisted leaf. Twisted leaf has, seriously

reduced production in 3 other orchards in Chelan and Yakima Counties, Wash.,

but insufficient information is available concerning the rate of spread of

twisted leaf to indicate its threat to the section.

Host Range and Varietal Susceptibility

The Bing variety of sweet cherry {Prumis av'mm) is severely affected.

Lambert, Napoleon (Royal Ann), Black Republican, and Black Tartarian

varieties, mazzard (P. avmm) seedhngs, and an unidentified variety of sour

cherry (P. ceram^) have been observed with very meager symptoms, but an

insufficient number of affected trees of these have been discovered to permit

conclusive statements regarding them. Limited experiments at Summerland,

British Columbia, indicate that peach (P. pérsica) is also affected. A few

Lambert and Napoleon trees remained symptomless after being budded with

diseased buds.

Symptoms

Cherry.—Affected Bing sweet cherry trees are usually severely stunted, with

shortening of the internodes particularly on the lateral branches. The spurs

form compact clusters or tufts of leaves. Individual leaves are small and much

distorted (pi. 19, top). Abrupt kinks occur in the midribs and petioles.

Leaf blades are frequently bilaterally unequal. The severest distortion is accompanied by necrosis of parts of the midribs or lateral veins. Mottling may

occur either as a peppering of small yellow spots with minute brown centers

or more rarely as rather bright yellow Hnes close beside some of the lateral

veins. Severe defoliation is sometimes observed (MO). Reeves (184) reported

severely misshapen fruits (pi. 19, top) on many trees in the Yakima Valley.

Distinctive fruit symptoms have rarely been observed in the Okanagan Valley.

Necrosis of the pedicel occurs when the fruit is misshapen. On cherry varieties other than Bing thus far observed, symptoms of twisted leaf have been

either very meager or absent. With the information now available, identifica135
136 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

tion of twisted leaf on cherry varieties other than Bing would be considered

doubtfuL

Peach,—At Summerland, British Columbia, twisted leaf has been transmitted from Bing sweet cherry to peach and back to Bing. The peaches

showed a marked reduction in vigor and a cankering of the bark on the trunks

and lower branches. Reeves has shown that peach trees inoculated with buds

from some twisted-leaf-affected cherry trees produced no symptoms, yet when

inocidating buds from other afiected trees were used splitting and cankering ot

the bark resulted; the bark-cankering symptom is interpreted by Reeves as

evidence that the cherry trees furnishing such inoculum were probably also

carrying ring spot virus. Thus, the peach can be infected by the twisted leal

virus, but the symptoms if any have not yet been definitely determined.

Diagnostic or Unusual Characteristics

Twisted leaf can be clearly diagnosed on Bing cherry by the characteristically

abruptly bent and twisted leaves. This eft'ect is caused by necrosis and differential inhibition of normal growth of tissue in the petioles and main and lateral

veins as compared with the leaf blade. Diagnosis on other varieties can be

made by indexing on Bing.

Transmission

Transmission has been effected experimentally by budding and grafting.

Preliminary-survey results indicate that spread usually takes place in the field

at a slow rate. An exception was noted in one Yakima Valley orchard where

a survey in 1946 showed a 15-percent increase of the disease during the preceding 3-year period.

Incubation Period

When inoculations Vv^ere made on cherry early in the growing season, symptoms appeared within 2 months. When inoculations were made in the fall,

symptoms appeared on the first growth formed in the spring.

Control Measures

Since the disease is known in only a relatively few orchards and there is

little evidence of rapid orchard spread, diseased trees should be removed. Evidence indicating spread by grafting pollinizer arms of mazzard carrying the

virus without recognizable symptoms onto Bing suggests the advisability o±

testing such polhnizer trees by indexing on Bing cherry before general use.

Budwood sources in affected districts should similarly be tested lest the disease

become widely disseminated in nursery stock.

Remarks

Severely and mildly affected Bing cherry trees have been observed in orchards.

When transfers were made from such trees to Bing nursery trees, symptom

expression agreed with that on the source material, indicating the presence

of strains of the virus capable of producing different degrees of symptom

expression. Serial transmission tended to reduce the severity of symptoms.
BLACK CANKER

By S. M. ZEILER, J. R. KIENHOLZ, and J. A. MILBRATH

Name of the Causal Virus

Black canker virus.

History and Geographic Distribution

Black canker has been known in Oregon for about 25 years, but its nature

was not determined until recently (267). It has been found in Hood River,

Polk, Union, Wasco, and Washington Counties, Oreg. Reeves ^^ reported

"what appears to be the same disease" in Douglas and Yakima Counties, Wash.

Lott ^^ found a similar canker on a number of Napoleon (Royal Ann) trees

in Okanagan Valley, British Columbia, Canada.

Economic Importance

Black canker is of little economic significance, because relatively few trees

are affected. Most affected trees bear about as well as normal ones, but in

certain instances black canker does considerable damage by causing severe

dieback and thereby reducing fruiting wood.

Host Range

Black canker is known positively on only the Napoleon variety of sweet

' Reeves, E. L. Unpublished data.

' Lott, T. B. Unpublished data.

Figure 47.—Two- to four-year-old twigs of Napoleon cherry affected with

black canker.

137
138 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

cherry {'Prunus avhim) in Oregon. The disease that Reeves -^ reported occurs

also on the Bing, Black Republican, and Deacon varieties.

Symptoms

Cankers start on 1-year-old twigs, first as slightly swollen areas in which

the bark splits lengthwise. These areas grow into rough black cankers, of

which the ultimate size is more or less determined by the size of the affected

branch {ñg. 47). Some infected trees are very severely cankered, while others

may have very few cankers. In severe cases dieback results indirectly from

the cankers. No abnormal fruits and no leaf symptoms have been observed.

Transmission and Incubation Period

Transmission was brought about by graft inoculation, after a 2-year incubation period. No natural spread of the disease has been observed, but there is

considerable evidence of spread through diseased propagation wood (buds or

scions).

Control Measures

Budwood should be selected from uninfected trees.

Remarks

Many attempts to isolate a causal organism have failed.

^*^See footnote 26, p. 137.
CHERRY RUGOSE MOSAIC

By H. EARL THOMAS and T. E. RAWLINS

Other Common Names of the Disease

Cherry mosaic 1.

Name of the Causal Virus

Festina lente Thomas.

Geographic Distribution

Occasional trees affected with cherry rugose mosaic have been seen in

Alameda, Butte, Napa, Riverside, Santa Cruz, Solano, Sonoma, Sutter, and

Tulare Counties, Calif.

Economic Importance

Observations begun in 193 5 indicate that damage to infected trees is not

great in any short period of years {23}). The disease does not seem to be

spreading readily in orchards.

Host Range

Natural infection is recognized on the Black Tartarian, Burbank, Napoleon

(Royal Ann), Black Republican, and Rockport varieties of sweet cherry

{Prunus avium). The virus was transmitted artificially to almond (P. amygdalus), peach (P. pérsica), and mahaleb cherry (P. mahaleb), and mild symptoms resulted.

figure 48.—Napoleon cherry leaves naturally affected with cherry rugose mosaic.

139
140 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Symptoms

The most obvious symptom is in the leaf blade and consists primarily in a

general chlorosis typically midway between the midvein and the leaf margin

and accompanied by considerable distortion (fig. 48). Smaller lenticular

chlorotic areas often appear along the lateral veins. Such affected leaves usually

shrivel and drop by late June or July. The yield of fruit seems to be somewhat reduced, and certain individual fruits appear somewhat flattened on the

suture side and more angular than normal.

Transmiission

The disease is transmitted by grafting.

Incubation Period

Small Napoleon and mazzard trees inoculated by buds or scions from

diseased trees in May and June developed symptoms early the following spring.

Control Measures

No specific measures have been undertaken to control cherry rugose mosaic.

The use of buds from disease-free trees is advised.
TATTER LEAF

By R. S. WiLLisoN, G. H. BERKELEY, and E. M. HILDEBRAND

Other Common Names of the Disease

The names "shredded leaf," "lace leaf," "ring spot," "necrotic ring spot,"

and "shot hole" have also been applied in various parts of the United States to

similar, but not necessarily identical, viroses of sweet cherry.

Name of the Causal Virus

Tatter leaf virus.

Geographic Distribution

Tatter leaf has been found on sv^eet cherries on the Niagara Peninsula,

Ontario, Canada, and in New York. A lace leaf condition has also been reported on sweet cherries in Washington (183) and Oregon (256).

Economic Importance

In Ontario tatter leaf is regarded as being of considerable importance on

sweet cherry and of potential importance on sour cherry. Most of the susceptible sweet cherry varieties do not appear to be seriously affected by the

disease, but field observations, supplemented by information from growers,

indicate that the fruits of infected trees of certain varieties fail to ripen properly and that the general vigor of other varieties is impaired. In a survey

conducted in Ontario in 1947 the incidence of tatter leaf was found to range

from 0.6 to 41.3 percent in 24 of 26 sweet cherry orchards selected at random.

In all, 2,649 trees were examined; of these 226, or 8.5 percent, were definitely

affected with tatter leaf. An additional 371 trees, or 14 percent, showed mild

symptoms suggestive of tatter leaf.

In New York (95) reduced vitality, accompanied by winter injury and

reduction in yield and longevity, is associated with a tatter leaf condition in

sweet cherry.

Host Range

The disease has been found in nature only on sweet cherry {Frumis aviuft^),

The known range of susceptible hosts comprises sweet cherry varieties Bing,

Giant, Black Tartarian, Deacon, Elkhorn, Governor Wood, Lambert, Napoleon

(Royal Ann), Schmidt, Seneca, Stark Gold, Windsor, Vernon, and Yellow

Spanish and seedlings; sour cherry (P. cerasus) variety Montmorency; peach

(P. pérsica) varieties Elberta and Rochester and seedlings; and mahaleb cherry

(P. -mahaleb) seedlings.

Transmission experiments indicate that domestica plum (P. domestica)

varieties Itahan Prune, German Prune, Lombard, and Reine Claude and Japanese plum (P. salicina) variety Abundance can also become infected, but

symptoms are frequently masked.

Symptoms

Sweet cherry.—At the beginning of the growing season in Ontario, fine

brown hnes appear on many of the expanding leaves, outlining narrow interveinal areas, which later become necrotic, drop out, and give the typical lacy

effect. Other leaves are mottled with yellow green or marked with oak-leaf

and line patterns or rings {£.g. 49). These symptoms usually persist throughout the summer but are found only on leaves formed early in the season. The

141
142 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Figure 49.—A, Twig of Yellow Spanish cherry affected with tatter leaf; B, affected

leaves of the same variety.
VIRUS DISEASES OF STONE FRUITS 143

later leaves are normal in appearance and tend to hide the symptom-bearing

leaves. Lacerations and patterns may reappear year after year, but in general

there seems to be some reduction in the amount of symptom expression after

the disease has become well established so that in time afifected trees may

sometimes become almost symptomless. Though observations on varietal

susceptibility are not yet complete, some differences in the reaction of diflierent varieties have been noted; for example, lacerations are less pronounced and

less numerous on Napoleon than on Black Tartarian, while on Bing the necrosis

often involves areas of the leaf surface larger than those just described and

the affected leaves are distorted and rugose. On the variety Deacon an additional symptom is the failure of the fruits to ripen properly, while afifected

trees of varieties Elkhorn and Seneca visually show reduced vigor and dieback.

A second form of the disease also has been observed in one orchard on the

Niagara Peninsula. Its symptoms differ from those already described in that

the stages preceding the appearance of necrosis and laceration are characterized

by red markings in place of the fine brown lines.

In New York severe terminal dieback was noted on Black Tartarian and

Napoleon cherry trees within 6 weeks after inoculation by means of dormant

diseased scions. Killing of young, vigorously growing Napoleon trees within

1 year was also recorded by Hildebrand.

Sour cherry.—In Ontario the first symptoms in the spring after artificial

inoculation of Montmorency sour cherry resembled those of necrotic ring spot

of sour cherry and consisted of fine translucent to dark-brownish, etched rings

up to about 2 mm. in diameter and frequently confluent. There were also

fawn-colored, red-rimmed necrotic spots of various shapes and sizes, which

usually dropped out. The other markings either remained unchanged or gradually faded out. These symptoms, which were present only on the first few

leaves to emerge, represent the initial, acute phase of infection.

In the second season there were some shiny lines and a trace of mottle and

etched rings on a few of the first leaves. The foliage put out before the end

of June was slightly rugose and undulant, but the later leaves developed

normally and gradually obscured the early-season symptoms. In early July

a few leaves turned yellow toward the base and dropped. A similar sequence

occurred in the third year, but during the last 10 days of June there was considerable casting of yellow leaves marked with green pin spots. While the

general effect was that of sour cherry yellows, the leaf markings were not

quite characteristic of that disease.

In the third and subsequent years the leaves were shed 2 to 3 weeks earlier

than usual in the fall.

The New York strains did not induce yellowing and premature dropping

of Montmorency leaves except when mixed with a strain of the prune dwarf

virus (92), but they caused severe terminal dieback of young trees inoculated

by dormant grafting in the field. In the greenhouse Montmorency responded

to some of these strains with terminal dieback and foliar symptoms very

similar to those of necrotic ring spot of sour cherry.

Peach.—The initial, acute phase of the disease on peach was characterized

by small green or yellow-green rings and by chlorotic and necrotic spotting of

the first leaves to emerge the spring after inoculation. Slight superficial bark

necrosis also occurred at this time, and more or less laceration of a few leaves

appeared later in the season.

In later stages of infection the acute phase did not occur, but about the
144 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

middle of the summer of the second and subsequent years scattered leaves

throughout affected trees sometimes showed faint but definite mosaic markings, oak-leaf patterns, rings, or a premature aging of the upper leaf surface,

which looks as if there were a very thin, finely checked, dull, dirty-yellow

encrustation on it. On seedlings budded with tatter-leaf-affected material in

the fall and cut back to the bud in the spring, the acute phase did not occur

and the midseason symptoms appeared during the first season.

On peach, in New York, some strains of the virus induced terminal dieback

and shortening of internodes, followed by recovery. Stem cankers appeared

on peach after inoculation with a strain from a Yellow Spanish sweet cherry

tree which had shown effects of winter injury only.

Peach trees inoculated with the Oregon strain sustained severe initial shock

and showed lacy leaves scattered over the tree, dieback of branches, and large,

sunken cankers around the inserted cherry buds (256).

Vlum,—The plum varieties tested so far in Ontario and New York were

little affected by tatter leaf; German Prune was symptomless, and Italian

Prune, Lombard, and Reine Claude sometimes showed only very faint mottling

or oak-leaf patterns. Scattered pinholes were observed in some of the midseason leaves of Abundance.

The virus strain associated with the second form occurring in Ontario

induced symptoms on Italian Prune and peach that were indistinguishable

from those associated with prune dwarf on these hosts, suggesting the presence

of the prune dwarf virus in this bud source.

A New York strain which induced prune dwarf symptoms on Italian Prune

{92) was shown to be much more heat-sensitive than the other strains.

Diagnostic or Unusual Characteristics

The laceration and chlorotic pattern on the first-formed cherry leaves in

the early stages of infection are diagnostic of tatter leaf in Ontario, but in

later stages the disease may sometimes be more or less masked. The disease is

characterized by acute and chronic phases on most of the susceptible hosts.

Severe dieback, sometimes followed by death of young trees of certain

varieties of sweet cherry, is regarded as characteristic of the disease in New

York.

Transmission

Tatter leaf is easily transmissible by budding or grafting. No insect vector

has yet been discovered, although considerable work has been done on this

phase in New York.

Incubation Period

In outdoor experiments symptoms were not apparent on any of the hosts

until the beginning of the next growing season after inoculation by budding

or patch grafting even when the trees were inoculated as early as June. Two

or more years may be required for the disease to become systemic in sweet

cherry trees more than 2 years old.

Hildebrand found that in the field the incubation period on sweet cherry

could be shortened to 1 month or less by grafting with dormant diseased

scions just before growth starts. In the greenhouse symptoms appeared on

rapidly growing seedhngs of this species h\ 2 or 3 weeks after budding at

different times during the growing season.

Control Measures

Roguing of diseased trees or seedlings is practicable in nursery rows, but not
VIRUS DISEASES OF STONE FRUITS 145

in orchards more than 2 years old. The iise of indexed disease-free sources of

scion and stock is recommended for propagation purposes.

Remarks

Although the symptoms induced on Montmorency sour cherry in the first

year more or less resembled those of necrotic ring spot of sour cherry and in

the third those of sour cherry 3^ellows, the reactions of the differential hosts

distinguish the tatter leaf virus with which Willison and Berkeley {249)

worked from both of these sour cherry viruses as found in Ontario. Briefly,

the separation is based on the following considerations.

In the first season the necrotic ring spot virus strains worked with in Ontario

caused necrotic flecking on prune leaves and on peach a number of acute

symptoms including delayed foUation and dieback, but they caused no annually recurring, chronic symptoms hke those of tatter leaf. The symptoms

induced on peach by return inoculations from Montmorency sour cherry

artificially infected with tatter leaf were those described for tatter leaf, not

for necrotic ring spot. Furthermore, in the Ontario trials the necrotic ring

spot virus produced neither the typical tatter leaf, or lace leaf, conditions on

sweet cherry nor the accompanying leaf markings; nor did it alone cause on

Montmorency the sequence of symptoms described for tatter leaf.

It would also appear that the sour cherry yellows virus is not involved.

The cherry yellows virus strains in Ontario and for that matter in eastern

United States have all been found in combination with necrotic ring spot.

The symptoms caused by combinations of sour cherry yellows and necrotic

ring spot viruses also differ from those caused by tatter leaf virus. In the first

place, these virus combinations induced internode shortening and persistent

rosetting on peach, symptoms not associated with tatter leaf on peach in

Ontario, as well as the acute symptoms characteristic of necrotic ring spot. In

the second place, they did not cause typical tatter leaf markings and lacerations on sweet cherries.

In spite of the resemblance of the respective symptoms on sweet cherry, the

tatter leaf condition found in New York was obviously caused either by a

virus, or a strain of virus, differing in many important details from that found

in Ontario or by a mixture of viruses. It is agreed that the diflerential-host

reactions obtained by Hildebrand with the New York strains were very similar

to, if not identical with, those obtained with the virus or virus complex causing

necrotic ring spot of sour cherries. The reaction of peach to lace leaf of sweet

cherry in Oregon {256) suggests affinity between that virus and the ring spot

complex. Cochran and Hutchins {62) also obtained lace leaf symptoms on

sweet cherry by inoculating with ring spot virus of peach. It seems probable

therefore that at least two viruses are involved; their identities cannot always

be readily distinguished by inspection of their symptoms either on sour or on

sweet cherry, but they can be separated by differences in their effects on a

range of differential hosts.

Furthermore, the possibility that the tatter leaf virus can be contaminated

with other viruses such as necrotic ring spot and prune dwarf or vice versa

should not be overlooked. From the practical point of view it may not matter

much which virus is present, since neither virosis is desirable in an orchard or

nursery, but their separation and recognition is important to the fundamental

knowledge of the highly complex cherry virus problem. However, much

remains to be done—both in continuing the differential-host-range studies

and in supplementing them by other methods—before complete clarification

is reached.

891793 0—51—13
146 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Since prune dwarf virus strains may be carried more or less masked in sweet

cherries (92, 246), the appearance of prune dwarf symptoms on Itahan Prune

or Lombard plum upon inoculation with the tatter leaf virus can be attributed to a mixture of tatter leaf and prune dwarf viruses in the affected

sweet cherry under investigation.
PINTO LEAF

By J. R. KIENHOLZ

Other Common Names of the Disease

None.

Name of the Causal Virus

Marmor pintofolium Kienholz (126).

History and Geographic Distribution

Pinto leaf was discovered at The Dalles, Greg., in June 1943 on Napoleon

(Royal Ann) cherry. Later it was found at Hood River, Greg., on mazzard

seedlings. It is known definitely at these two localities only, but there is an

unconfirmed report that it was seen at Kennewick, Wash.

Economic Importance

Pinto leaf is of very minor importance because of its limited occurrence.

It is potentially dangerous if spread occurs, the degree of injury being about

the same as that from mottle leaf.

Host Range

The disease has been found occurring naturally in the field on sweet cherry

{Prunus avium) varieties Napoleon, Black Republican, and Stark Gold and on

mazzard (P. avium) seedlings. Attempts have been made to transmit the

trouble to sour cherry (P. cerasus), peach (P. pérsica), domestica plum (P.

Figure 50.—Napoleon cherry leaves affected with pinto leaf.

147
148 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

domestica) ^ apricot (P. armeniaca) ^ western chokecherry (P. vhginiana var.

demissa), rose (Rosa sp.), apple {Malus sylvestris), and pear {Pyrus commtmis) • but the difficulty of budding in the dry Dalles district makes these

tests somewhat inconclusive.

Symptoms

Pale-green or yellowish patches on the leaves (fig. 50) soon change to bright

yellow or white. No specific pattern is formed, but the small to large patches

occur on any part of the leaf. Leaf symptoms are sometimes meager or

obscure, particularly on mazzard seedUngs, on which they often appear merely

as a coarse stippling. Leaves on terminal shoots are rarely affected until late

in the season when a few of the basal leaves may show the symptoms. A

slight stunting of the trees occurs after several years, presumably because of

the reduction of chlorophyll in the leaves.

The fruits never quite reach full maturity in color or taste, being rather

insipid, like the fruits from trees affected with mottle leaf.

Transmission

So far pinto leaf has been transmitted by budding only.

Incubation Period

Trees bud-inoculated during the early fall show leaf symptoms early the

following spring.

Control Measures

At present no control measures have been tried.
ROUGH BARK OF ORIENTAL FLOWERING

CHERRY

By J. A. MiLBRATH and S. M. ZELLER

Names of the Causal Virus

In accordance with Holmes' system of classification the name ^^Rhnocortms

kwanzani Milbrath and Zeller" was applied to the virus and 'Trunus virus 9

Milbrath and Zeller" was assigned in accordance with Smith's system {15 5),

Geographic Distribution

The disease has been reported from Oregon only.

Economic Importance

Serious losses were sustained in nurseries from poor bud set and the production of misshapen, dwarfed trees until rough bark was eliminated from the

stock. Affected trees do not recover and are therefore a complete loss.

Host Range and Varietal Susceptibility

Only the Kwanzan variety of oriental flowering cherry {Pnmus serrulata)

is known to be naturally affected. Shirotae (Mount Fuji), Naden, and Shirofugen varieties have been artificially infected. Mazzard (P. avhun) seedlings,

the Bing, Napoleon (Royal Ann), and Lambert varieties of sweet cherry (P.

avmm), and the J. H. fiale peach (P. pérsica)^ all of which also have been

artificially infected, retain the rough bark virus without symptom expression.

Normal vigorous shoots of mazzard often grow from the base of infected

Kwanzan trees. Such mazzard understock retains the virus.

Symptoms

Nursery trees of oriental flowering cherry variety Kwanzan propagated

from infected stock are dwarfed by extreme shortening of the internodes,

which makes the leaves close together in clusters. Areas on the midribs of the

leaves become necrotic and crack, causing the leaves to arch downward (üg.

51, A). The dwarfing of the growth and the curving of the leaves cause an

effect similar to that caused by aphid injury. The bark of current-season

growth becomes deep brown and roughened by longitudinal splitting (fig. 51,

JB). This splitting often originates at lenticels. On wood 2 years old or older

this splitting and the rough bark condition become more pronounced and new

growth continues to be much reduced. Shiro-fugen develops much the same

symptoms as Kwanzan except that the bark splitting is not so evident. Naden

develops only a slight cupping of some of the leaves as a result of necrosis and

splitting of the midrib and main lateral veins. The growth is not dwarfed,

and no bark splitting occurs. Shirotae does not show any definite symptoms.

Transmission

The virus is readily transmitted by budding or grafting. Complete organic

union is not necessary, and in many cases the virus is transmitted even when

the bud dies shortly after budding. Many mazzard seedlings budded in the

nursery were infected even when there was no apparent union between the

Kwanzan bud shield and the mazzard rootstock.

149
150 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Incubation Period

Kwanzan bud-inoculated in August or September shows

throughout the tree as soon as new growth develops in the spring.

symptoms

Figure 51.—A, Current-season branch of Kwanzan oriental flowering cherry affected

with rough bark, showing characteristic cupping and arching of leaves; B, older

branch showing severe splitting and rough bark caused by the virus.
VIRUS DISEASES OF STONE FRUITS 151

Control Measures

The disease has been eHminated from the nurseries in Oregon by removing

infected trees from the mother block and by using budwood from only Kwanzan trees showing good growth without rough bark.
VIRUS DISEASES OF SOUR CHERRY

SOUR CHERRY YELLOWS

By G. W. KEITT, G. H. BERKELEY, DONALD CATION, C. N. CLAYTON,

E. M. HILDEBRAND, J, DUAIN MOORE, and E. J. RASMUSSEN

Other Common Names of the Disease

Yellow leaf (76, 177, 215), physiological leaf drop {68, 96), physiological

yellow leaf (175), physiological yellows (177), boarder tree (124) and virus

leaf drop (159).

Names of the Causal Virus

The common name is ''sour cherry yellows virus or viruses" (124), Hildebrand (91) proposed the name "Chlorogenus cerasae7'

Geographic Distribution

Sour cherry yellows or diseases with symptoms closely conforming to those

of sour cherry yellows have been reported in the United States in California,-^

Idaho (20),^^ Indiana,^! lowa,^^ Michigan (175, 176), Missouri,^^ Montana,^^ New Hampshire,^^ New York (68, 76, 98, 21 5), North Carolina (54),

Ohio,^^ Oregon,^^ Pennsylvania (137, 13 8), Utah,^« Washington (184),^^

and Wisconsin (121, 122, 123) and in Canada in British Columbia ^*^ and

Ontario (8). More or less sour cherry yellows has been found by Moore and

Keitt to occur commonly in the sour cherry nursery stocks that they have

indexed, though symptoms may not have been expressed in the nursery and the

disease may not have been recorded in the States in which the nurseries were

located.

Economic Importance

Yellows appears to be economically the most important known virus disease

of sour cherry in the United States and Canada, It is widely distributed in the

main areas of commercial sour cherry production in these countries. The percentage of trees affected varies greatly in different orchards. In some old

orchards all or nearly all the trees are diseased. The rate of spread of the

disease varies with the orchard and the season. Surveys in Wisconsin indicated annual increases in the percentage (based on total number of trees) of

diseased trees per orchard commonly ranging from about 1 to 10 percent and

averaging approximately 3 (124), Somewhat higher rates of spread were

reported from Michigan by Rasmussen and Cation and from Ontario (250),

^^ Wilson, E. E. Unpublished data.

^"^ Blodgett, E. C. Unpublished data.

'' Shay, J. R. Unpublished data.

^^ Buchholtz, W. F. Unpublished data.

^Hliilikan, D. F. Unpublished data.

^^ Morris, H. E. Unpublished data.

^ Rasmussen, E. J, Unpublished data.

'"" Winter, H. F. ^ Unpubhshcd data.

^^ Zeller, S. M. Unpublished data.

""^ Richards, B. L., and Keitt, G. W. Unpublished data.

^"^ Reeves, E. L., Johnson, F., Blodgett, E. C, and Keitt, G. W. Unpublished data.

'*" Foster, W. R. Unpublished data.

152
VIRUS DISEASES OF STONE FRUITS 153

Yields from diseased trees fall ofli at variable rates and to variable extents.

Commonly within 2 to 5 years after the first symptom expression the yield

in Wisconsin may be reduced half or more (160). Trees that have been

diseased for many years may show much greater reduction in yield. Attempts

by Hildebrand (90), Rasmussen and Cation (177), and Moore and Keitt to

restore the fruitfulness of trees affected with yellows have been unsuccessful.

Host Range

At present it is not possible to give an unqualified statement as to the host

range or symptomatology of yellows. It is possible that more than one virus is

concerned in the etiology and that each virus may have different strains.

Numerous viruses and many strains may affect the species of Prtmus used in

the host-range studies. In some cases a species of Primus inoculated with a

virus, such as the necrotic ring spot virus of sour cherry, will show symptoms

the first year and later carry the virus without showing further symptoms.

Consequently, the facts that a host shows symptoms of virosis after inoculation

with buds from a source of cherry yellows and that cherry yellows can be recovered from the intermediate host do not necessarily prove that the symptoms

on the intermediate host were incited by the cherry yellows virus or virus

complex. They may have been incited by one component of a cherry yellows

virus complex or by some other virus or viruses carried in the scion, the stock,

or both.

The following paragraphs are intended to present the available information,

which is recognized as incomplete and in some aspects probably subject to

reinterpretation in the hght of future findings.

Symptoms characteristic of yellows are found in orchards and nurseries on

sour cherry (P. cerastes) varieties Montmorency, Early Richmond, and EngUsh

Morello. Yellows has been transmitted by budding or some other grafting

method from Montmorency sour cherry to sour cherry varieties Montmorency,

Early Richmond, and English Morello, and leaf symptoms characteristic of

yellows have appeared. In greenhouse studies Moore and Keitt have transmitted cherry yellows back to Montmorency from all the cherry varieties just

listed.

In Wisconsin Moore and Keitt have transmitted the virus or virus complex

by budding from Montmorency sour cherry through each of the following

hosts and back to Montmorency without the expression on these intermediate

hosts of any recognized symptom characteristic of yellows on sour cherry:

Sweet cherry (P. avmm) varieties Bing, Napoleon (Royal Ann), and Black

Tartarian and mazzard (P. avmm) seedlings; peach (P. pérsica) varieties

Elberta, Halehaven, and Rochester; domestica plum (P. domestica) varieties

Bradshaw, Italian Prune, and Lombard; American plum (P. americana) seedlings; duke cherry variety Royal Duke; myrobalan plum (P. cerasifera) seedlings; mahaleb cherry (P. mahaleb) seedlings; black cherry (P. serótina)

seedlings; eastern chokecherry (P. virginiana) seedKngs; and pin cherry (P.

pensylvanica) seedlings. Leaf symptoms different from those of yellows on

sour cherry occurred on all these intermediate hosts, but they were not clearly

distinguishable in these experiments from symptoms on the same hosts budded

comparatively with buds from Montmorency affected with necrotic ring spot

alone. They are, therefore, not attributed to yellows though it is recognized

that the necrotic ring spot virus may be a part of a yellows virus complex and

that further experiments may reveal differential symptoms on some of these

hosts when they are budded comparatively with buds affected with yellows and
154 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

with buds affected with necrotic ring spot but not with yellows. All attempts

to transmit cherry yellows from Montmorency to Japanese plum (P. salicina)

varieties Abundance and Burbank failed. No symptoms were produced on

these two varieties, and yellows was not recovered from them by budding back

to Montmorency (163),

In Ontario, New York, and Michigan the sour cherry yellows virus or virus

complex was transmitted by grafting to peach varieties Elberta, J. H. Hale,

South Haven, Halehaven, Kalhaven, Fertile Hale, and Rochester; to peach

seedlings; to domestica plum varieties Italian Prune and Lombard; and to

mahaleb cherry—by Berkeley, Hildebrand, and Rasmussen and Cation.

A fuller understanding of host relationships and symptoms must await

further clarification of the relations of sour cherry yellows, necrotic ring spot,

and possibly other virus diseases.

Symptoms

Sour cherry.—The most striking symptom on Montmorency sour cherry is

yellow and green mottling of some of the leaves (pi. 20, A, B), followed by

leaf casting. Chlorosis appears first as irregular pale-green or yellov/ish areas

anywhere on the leaf lamina and may progress until the entire leaf is yellow.

Some leaves may retain the green color longest along the larger veins (pi. 2 0,

B). Leaves may be cast before any chlorosis is visible or at any stage of yellowing. The older leaves generally show symptoms first, often beginning with the

scale leaves. When favorable conditions continue symptoms usually appear on

the next younger leaves in the order of their age. If a wave of yellows is

interrupted by a period of weather unfavorable for symptom expression, one or

more leaves on a shoot may remain apparently healthy whereas leaves farther

up the shoot may develop typical symptoms after favorable conditions resume.

Most trees that have been diseased several years tend to have larger and fewer

leaves than normal.

In the orchard the first wave of yellows is usually the most severe. In Door

County, Wis., and in other areas with similar climates, it usually comes about

3 or 4 weeks after petal fall. Other waves of varying severity may occur

until fall. The amount of defoliation due to yellows is variable, ranging from

a trace to more than 50 percent of the leaves.

Trees of bearing age that have had yellows for several years generally show

a much reduced spur system and a variable reduction in yield, averaging about

50 percent or more. The fruits average larger than normal and are of good

quality.

Fewer leaf buds seem to be diiferentiated on the shorter terminal twigs on

trees affected with yellows than on healthy trees. Furthermore, according to

Moore and Keitt, leaf buds on yellows trees tend to grow into shoots (pi. 20,

C). Thus there are more shoots, which tend to be somewhat shorter and

thicker than those on healthy trees. The trees eventually develop a willowy

type of growth (pi. 20, C), with long, bare spaces on the twigs, and the crop

is produced largely on the shoots grown in the preceding season. Trees affected

with yellows apparently may live about as long as healthy ones, but their

trunks and branches tend to be more subject to breakage in windstorms {124).

The same symptoms were produced on Early Richmond sour cherry as on

Montmorency {124).

The same leaf symptoms occurred on English Morello as on Montmorency.

In Moore and Keitt's greenhouse work leaf symptoms did not appear until the

third year after budding. In that year some English Morello fruits approach-
VIRUS DISEASES OF STONE FRUITS 155

ing maturity developed small necrotic lesions, usually internal, and became

more or less distorted.

Peach.—In work conducted by Berkeley (8)y Hildebrand (84, 87), and

Rasmussen and Cation (176) with peach seedlings and varieties Elberta and

Rochester, it was found that trees budded in the field in the fall with buds

affected with the cherry yellows complex showed considerable necrosis, dieback, rosetting, and stunting of shoots. However, trees budded with buds

affected with necrotic ring spot alone did not show rosetting, though necrosis

and dieback were present. Moreover, such trees tended to recover, whereas

when the cherry yellows virus was present the rosetting and stunting persisted

from year to year. This differential reaction was reported to be clearly

demonstrated when seedlings were cut back in the spring close to buds that

had been inserted near the ground line in the fall. When cherry yellows virus

was present, the shoots were dwarfed and rosetted (ñg, 52). When cherry

yellows virus was absent, the shoots were more or less normal, though some

mottling might be present.

In Wisconsin greenhouse studies by Moore and Keitt with Elberta, Halehaven, and Rochester varieties of peach, inoculations at bud break with buds

from two sources of cherry yellows incited rosetting only on Halehaven and

only in the year of inoculation. Budding with material from two sources of

necrotic ring spot alone did not incite rosetting on any of the three varieties.

After two seasons in pots kept in the greenhouse except over summer, when

they were out of doors, these trees were removed from the pots and planted in

the field. There have been no rosette symptoms in the field, but yellows has

been transmitted back to sour cherry from all three peach varieties budded

originally with buds affected with yellows.

Phifn.—In Ontario in the year after budding of Italian Prune and Lombard

plums with buds affected with cherry yellows, small necrotic spots and some

shot holes were present on a few first-formed leaves on the twig above the bud

insertion. The following year definite prune dwarf symptoms were present on

several branches. In this connection it was noted that, when Italian Prune

was budded with buds affected with necrotic ring spot, small necrotic spotting

also resulted on unfolding leaves, but prune dwarf symptoms were lacking.

This suggested that the necrotic spotting was most likely due to the necrotic

ring spot virus. In support of this hypothesis is the fact that in Berkeley's

experiments buds infected with sour cherry yellows virus from two other

sources known to contain the necrotic ring spot factor did not give rise to

prune dwarf symptoms, but they did give rise to only the necrotic spotting

referred to previously. Further data and possible explanations of the similarities and differences of symptom expression of cherry yellows and prune

dwarf were given by Berkeley and Willison (9).

In greenhouse experiments by Moore and Keitt in Wisconsin, potted Italian

Prune trees were inoculated by budding from the following virus sources:

(1) Two Montmorency trees affected with necrotic ring spot, but not with

yellows; (2) ûye Montmorency trees affected with sour cherry yellows and

known to contain the necrotic ring spot virus that is latent on Montmorency

after one season of symptom expression; and (3) one Montmorency tree

affected with yellows and known to contain a strain of necrotic ring spot virus

that incites striking recurrent symptoms on Montmorency annually. Each

inoculated Italian Prune tree received two buds from a single tree of the given

source, and four unbudded trees served as controls. All the budded prune
156 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Figure 52.—A, Peach seedling in a nursery row, shelving resetting frequently occurring after inoculation with material affected with sour cherry yello'ws; B, comparable uninoculated seedling.

trees developed chlorotic etch ring leaf symptoms in the year of inoculation.

Striking prune dwarf symptoms developed the year after inoculation and in

succeeding years on all trees inoculated with buds from Montmorency affected

with yellows and known to contain latent necrotic ring spot virus. Prune

dwarf symptoms have not been expressed on the trees inoculated with buds

carrying the necrotic ring spot virus without yellows or on those inoculated

with buds from the tree showing symptoms of yellows and carrying the strain

of necrotic ring spot virus that incites symptoms annually on Montmorency.

No symptoms of any kind have been expressed on the unbudded control trees.

By budding back to Montmorency from Italian Prune, both necrotic ring
VIRUS DISEASES OF STONE FRUITS 157

spot and yellows were transmitted from trees that had been inoculated

originally with buds from yellows-aííected cherry; necrotic ring spot only was

recovered from those budded originally from the source of necrotic ring spot

alone, and nothing was transmitted from the unbudded controls. It is especially noteworthy that the Italian Prune budded originally with Montmorency

buds carrying the viruses of yellows and recurrent necrotic ring spot transmitted both yellows and recurrent necrotic ring spot back to Montmorency,

even though no prune dwarf symptoms had been expressed on the Italian

Prune.

Transmission

Yellows has been transmitted experimentally by budding or other methods

of grafting (121); in nature it is transmitted by unknown means, probably

insects. Cation (51) recently reported that this disease can be transmitted

through the seeds of mahaleb cherry.

Incubation Period

In the field, symptoms usually appear under favorable climatic conditions

within 1 to 2 years after budding or grafting. In the greenhouse, by starting

with stocks and scions beginning to break bud and by maintaining suitable

temperatures, Moore and Keitt obtained leaf symptoms on Montmorency sour

cherry within a minimal period of 6 weeks. Hildebrand (S6) reported transmission of cherry yellows to peach with symptom expression in 3 weeks.

Thermal Relationships

In the greenhouse leaf symptoms of yellows were not expressed at an approximately constant temperature of 20° C. or higher, but typical ones

appeared at 16° or lower. Typical leaf symptoms developed if the night

temperature was 16° or lower even though the day temperature was 20° to

28° (125, 164). Temperature appears to be a major factor affecting regional

and seasonal expression of leaf symptoms of yellows (125, 159, 165),

Efforts to inactivate the virus in bud sticks by heat without killing the

buds have thus far been unsuccessful. Moore (161) transmitted yellows

from Montmorency bud sticks 15 cm. long and 2.7 to 3 mm. in diameter that

had been immersed in water at 50° C. for 22 minutes.

Control Measures

The first step in control should be the production of yellows-free nursery

stocks of superior quality. Since many nurseries supplying sour cherry stocks

are located in regions in which high temperature masks cherry yellows leaf

symptoms in most years, some indexing procedure is indicated. In Michigan, New York, and Ontario Rasmussen and Cation (176), Hildebrand (S4),

and Berkeley (8) have indexed sour cherry stocks on peach. In Wisconsin

indexing is done on sour cherry incubated in the greenhouse under favorable

conditions for yellows expression (166).

New plantings should be made at some distance from older orchards and

with stocks as free from yellows as possible. Berkeley, Hildebrand, Moore and

Keitt, and Rasmussen and Cation recommend that any trees affected with

yellows be removed from young plantings and replaced by healthy stock.

General recommendations regarding bearing orchards cannot be made until

the research program is further advanced. However, unless information to the

contrary becomes available, it is suggested that no roguing and replanting be

done in older orchards in which cherry yellows is well established, but that

entire blocks be removed when they become unprofitable. It appears generally
158 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

advisable to rogue yellows-infected trees in bearing orchards in which the

number of affected trees is comparatively very small.

Remarks

No case has yet been reported in which a sour cherry tree diseased with

yellows was shown beyond doubt to be free from the necrotic ring spot virus.

It is possible that sour cherry yellows is incited by a virus complex that

includes the necrotic ring spot virus.

There is evidence of the existence of various strains or complexes of yellows

and other viruses and of strain differences in sour cherry varieties in their

reaction to these virus entities (9, 8S, 92, 177).

In three cases following transfer of buds from Montmorency sour cherry

trees showing typical yellows symptoms to Montmorency, Berkeley and Moore

and Keitt obtained symptoms of green ring mottle. The trees from which

these buds were taken have not shown green ring mottle.
GREEN RING MOTTLE

By E. J. RASMUSSEN, G. H. BERKELEY, DONALD CATION, E. M. HILDEBRAND,

G. W. KEITT, and J. DUAIN MOORE

Other Common Names of the Disease

The disease has been called green ring yellows also.

Name of the Causal Virus

No Latin binomial has been suggested. The virus may be referred to as the

green ring mottle virus.

History and Geographic Distribution

Green ring mottle has been reported in sour cherry orchards in Michigan,

New York, and Wisconsin and in Ontario, Canada. It was first observed in

Michigan in 1937, in New York in 193 8, in Wisconsin in 1942, and in

Ontario in 1941. It has been found as a minor disease in several orchards in

Michigan, but it has been observed in but one orchard in Ontario. Since

the first report in the respective sections there has been but little spread of the

disease.

Economic Importance

At present green ring mottle is classed as of minor importance solely because

of its rare occurrence.

Host Range

Green ring mottle has been found in nature on sour cherry {Prunus cerasus)

only. It has been transmitted experimentally to sour cherry variety Montmorency; sweet cherry (P. avmfn) varieties Bing and Napoleon (Royal Ann) ;

and peach (P. pérsica) varieties Elberta, Rochester, Halehaven, and South

Haven and seedlings; and mahaleb cherry (P. mahaleb) seedlings.

Symptoms

Sour cherry.—^Characteristic symptoms appear on leaves of Montmorency

cherry 4 to 5 weeks after petal fall as green spots, rings, arcs, or irregular,

curved bands ^ to ^ inch in width distributed more or less evenly over a

yellow background (pi. 21, A). Affected leaves are cast. The period of

defoliation lasts for 10 to 14 days, after which affected trees appear to have

recovered. Another symptom consisting of scattered chlorotic spots on green

leaves may appear. This last-mentioned symptom is especially prominent in

the fall, when the green ring phase is absent, but it may appear in the spring

in association with the green ring phase. It was observed first by Berkeley in

Ontario, but was confirmed by Cation in Michigan.

As a rule the defoliation caused by green ring mottle is not as severe as that

associated with sour cherry yellows, though in Ontario Berkeley observed one

tree that had as severe defoliation as any seen in that Province in association

with yellows. Rasmussen (96) and Cation found that in Michigan defoliation does not recur year after year on the same trees as consistently as

it does with yellows. This does not hold apparently in Ontario and Wisconsin,

according to Berkeley and Moore and Keitt, since certain trees both in

nurseries and in orchards have shown symptoms annually for 5 or 6 years.

However, the amount of defoliation varies with individual trees. For instance,

five trees in one orchard in Ontario have shown consistent variation in this

159
160 HÄNDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

respect each year* One tree has shown severe defohation consistently, while

the defoliation of the other four has been moderate to mild each year. Nursery

trees in the greenhouse in Wisconsin have shown characteristic symptoms for 4

years. Hildebrand stated that defoliation is relatively light in most years and

practically absent in certain ones in New York.

Mahaleb cherry.—Pale chlorotic patterns on green mahaleb cherry leaves,

similar to the mottling and line patterns sometimes caused by the necrotic

ring spot and sour cherry yellows viruses, are induced by the green ring mottle

virus. The mottling tends to occur as rather indefinite to definite rings.

Affected leaves persist throughout the season. Since the necrotic ring spot

virus appears to be associated with the green ring mottle, the symptoms

described may have been caused by the former virus.

Sweet cherry,—In Wisconsin, Moore and Keitt found that the Bing variety

of sweet cherry is a symptomless carrier. According to Berkeley, inoculated

Napoleon trees showed a few leaves with a mild mottle in Ontario. Transfers

from these trees back to peach showed that a virus was present in the Napoleon

trees. Whether or not this mild mottle was caused by the necrotic ring spot

factor was not investigated.

Peach,—When peach seedlings or varieties are inoculated with the green

ring mottle virus, they react with mild shock symptoms of delayed foliation,

sometimes with and sometimes without varying amounts of twig dieback. They

outgrow these symptoms and appear to recover, though in some cases there is a

mild stunting of growth. Resetted shoots such as those associated with sour

cherry yellows are lacking. Inoculations with the severe type of green ring

mottle virus reported for Ontario resulted in severe symptoms on peach

seedlings and in the ultimate death of the Rochester variety.

From the symptom expressions on peach, Moore and Keitt and Berkeley

concluded that all the green ring mottle material used in transmission tests in

Wisconsin and in Ontario carried a virus of the necrotic ring spot type.

Diagnostic or Unusual Characteristics

The retention of the green coloring in the form of rings or spots on

Montmorency cherry leaves and the less drastic eft'ect on peach differentiate

green ring mottle from sour cherry yellows. On the other hand, the yellowing and casting of leaves by Montmorency cherry trees at the same period as

by trees affected with yellows and the apparent association of a necrotic ring

spot virus suggest a close relationship between green ring mottle and sour

cherry yellows. The fact that in both Wisconsin and Ontario inoculations with

material affected with typical sour cherry yellows gave symptoms of the green

ring mottle type supports this contention.

Transmission

Green ring mottle has been induced experimentally by budding only, and

its manner of spread in natvire is unknown.

Incubation Period

Bud inoculation in the fall produced symptoms the following spring when

growth was renewed.

Control Measures

Disease-free nursery stock should be obtained for new plantings. Source

Montmorency cherry trees used for bud sticks should be examined in June when

symptoms are expressed. The elimination of source trees which transmit

symptoms of necrotic ring spot by an indexing procedure should also eliminate
VIRUS DISEASES OF STONE FRUITS 161

green ring mottle. Affected trees in new plantings should be rogued. Control

measures in old orchards must await the result of further research.

Remarks

As already stated, green ring mottle has many points of similarity with sour

cherry yellows and may be caused by a strain of the yellows virus. A green

ring mottle has also been observed by Hildebrand in New York on both Italian

Prune (P. domestica) and its rootstock, myrobalan plum (P. cerasifera), The

relationship of these two mottles is under investigation. Hildebrand {^9) also

reported that infection with green ring mottle virus seemed to inhibit infection

with the leaf spot fungus, whereas this did not hold for yellows. However,

according to Moore and Keitt, there has been no evidence of this phenomenon

for green ring mottle in Wisconsin.

§91793°—JI—14
PINK FRUIT

By E. L. REEVES and LEE M. HUTCHINS

Other Common Names of the Disease

Pink cherry.

Name of the Causal Virus

Pink fruit virus.

History and Geographic Distribution

In 1934 the disease was reported in western Washington and symptoms were

described {SI), but transmissibility was not demonstrated. Investigations by

Reeves and Hutchins in 1940 (unpublished data referred to by Reeves {1S4))

established that pink fruit is a transmissible virus disease.

Pink fruit is widely distributed in the sour cherry orchards of western

Washington from Whatcom County in the north to Clark County in the

south. As a result of a brief survey made in 193 8, Reeves, Huber, and Baur

(186) reported 9 percent of the trees to be affected in certain selected

orchards in King and Pierce Counties in western Washington. Coe (66)

reported that an average of 2 percent of the sour cherry trees was found

affected with pink fruit in an orchard survey made in six western Washington

orchards during 1942. A disorder that appeared somewhat similar was

observed in Idaho and reported by Blodgett (H).

Economic Importance

Pink fruit, the cause of serious losses in many western Washington soiir

cherry orchards, is considered second in importance to brown rot, caused by

Monàinia laxa (Aderh. & Ruhl.) Honey, from the standpoint of reduction in

commercial production. There is some seasonal variability in the percentage

of fruits that develop severe symptoms of the disease. Generally, 2 5 percent

or more of the fruits are affected on a tree that has exhibited symptoms for 1

year or longer. It is considered impractical at harvesttime to pick the

apparently normal fruits and leave the severely affected; thus the result is a

total loss of the crop on affected trees.

Host Range

Montmorency is the only variety of sour cherry (Prunus cerasus) known to

be affected. Possibly other varieties of sour cherries or other species of Prunas

may be involved, but they have not been adequately tested.

Symptoms

The fruits exhibit the most conspicuous symptoms of pink fruit (pi. 21, JB),

and these symptoms can be most readily observed from about 2 weeks prior

to harvest until shortly thereafter. Affected fruits are smaller than normal,

insipid to bitter, pinkish yellow to dull pinkish brown, and with internal and

external brown necrotic areas in the flesh. The more immature of the

affected fruits tend to be conical, and all fruits exhibiting symptoms tend to

drop from the tree earlier than those appearing normal.

The leaves of affected trees often have a tendency to fold upward along

the midvein with the general result that the trees appear to be suffering from

a lack of moisture. Affected trees blossom late in the spring, and growth is

162
VIRUS DISEASES OF STONE FRUITS 163

suppressed. Late blossoming alone, however, is not an absolute criterion in

diagnosing the disease.

Transmission

Transmission has been efiFected only by grafting or some adaptation of the

grafting process and has been demonstrated by using either shoot or root

tissues.

Incubation Period

In field tests 15 months was the minimum incubation period, and in many

instances the first symptoms appeared 17 months after inoculation.

Control Measures

Records obtained and observations made from 1939 through 1944 indicate

that pink fruit has spread very slowly in some western Washington orchards

and not at all in others. Since trees do not recover from the disease and the

crops from affected trees are of no commercial value, it is considered that a

tree-removal program, together with the careful selection of nonaffected propagation wood, should be suggested as a control measure. Because of the slowness

with which the disease apparently spreads, it is even possible that a well-directed

control program might entirely eradicate the disease.

Fruit symptoms of pink fruit are similar to those of a disease called western

X little cherry which occurs on sour cherry in several Western States and which

has been related to the western X-disease of peach. Certain differences between

pink fruit and this so-called little cherry follow:

L When Montmorency trees on mahaleb rootstock are inoculated with buds from westernX-little-cherry-aííected trees, they wilt and decline; similar trees inoculated with the pink

fruit virus exhibit fruit symptoms^ but do not wilt.

2. Symptoms of western X-disease developed on leaves of peach trees inoculated with buds

from Montmorency trees afifected with western X little cherry, but not on those of trees

inoculated with the pink fruit virus.

3. The incubation period of pink fruit was found to be at least 15 months and often it was

17 months, but the incubation period of western X little cherry on sour cherry is 9 months,

when inoculations are made in the fall.

Further work needs to be done in comparing pink fruit and western X little

cherry to ascertain whether a relationship exists between these two diseases.
NECROTIC RING SPOT

By G. H. BERKELEY, DONALD CATION, E. M. HILDEBRAND,

G. W. KEITT, and J. DUAIN MOOKE '^

Other Common Names of the Disease

Ring spot, shredded leaf, necrotic leaf spot, and small leaf.

Name of the Causal Virus

Necrotic ring spot virus.

History and Geographic Distribution

In Ontario, Canada, necrotic ring spot was first observed in 1939 and its

virus nature was demonstrated in 1940 when typical symptoms were expressed

on Montmorency sour cherry and a variety of duke cherry as a result of

inoculations by budding from infected trees (2W). At about the same time

sour cherry necrotic ring spot, or a closely related disease, was discovered

independently in New York, Wisconsin, Pennsylvania, and Michigan.

Economic Importance

The data on economic importance are not conclusive. In Wisconsin, according to Moore and Keitt's report, the common strains of necrotic ring spot virus

have not been shown to have any harmful effect on the fruiting habit or

yield of Montmorency sour cherry except possibly in the year when acute

symptoms are severe (252). In Ontario, there are indications that necrotic

ring spot apparently has some reducing effect on yield, and the thinness of

the foliage of affected trees would appear to support these indications. From

records on yields of healthy trees and of those affected with necrotic ring spot

in three orchards, Berkeley noted a gradual reduction in one orchard but no

appreciable consistent reduction in the other two. In New York increased

susceptibility to winter injury was associated with the presence of necrotic

ring spot (90). In Michigan, where the disease is prevalent in most orchards,

no reduction in leaf size or indications of reduced yields have been apparent,

but comparisons of affected with virus-free stock have not been made.

Host Range

The disease has been found naturally on sour cherry (Pnmus cerasus) and

chokecherry (P. virginiana). It has been transmitted by budding or grafting

to sweet cherry (P. avium) seedlings and varieties Bing, Napoleon (Royal

Ann), Black Tartarian, Giant, and Eagle; to mazzard (P. av'min) seedlings;

to peach (P. pérsica) seedlings and varieties Elberta, Rochester, and Halehaven;

to domestica plum (P. domestica) varieties Bradshaw, Italian Prune, and

Lombard; to American plum (P. americana) seedlings; to various wild and

ornamental species of Prunus: Bessey cherry (P. besseyi), a Hansen bushcherry, sand cherry (P. pumila), pin cherry (P. pensylvanica), and chokecherry (P. virginiana) ; to duke cherry (P. avitim X P- cerasus) varieties

Royal Duke and Grand Duke; to myrobalan plum (P. cerasifera) and

mahaleb cherry (P. mahaleb) rootstocks; and to sour cherry (P. cerasus)

varieties Montmorency, Early Richmond, and Enghsh Morello. Cucumber

{Cucttmis safivus L.) was infected from sour cherry by rubbing juice on it.

Senior authorship of this section is by mutual agreement and not by priority of publication.

164
VIRUS DISEASES OF STONE FRUITS 165

In the Wisconsin host-range studies (163) the following hosts in the list

just given were not tested by Moore and Keitt: P. avmm varieties Giant and

Eagle; P. pérsica seedlings; and the Grand Duke variety of P. avmm X i*.

cerastis. Necrotic ring spot was transmitted by budding back to Montmorency, with the expression of typical symptoms, from all other hosts hsted

except P. ptLmila with which no transmission was attempted.

All attempts by Moore and Keitt to transmit necrotic ring spot from

Montmorency sour cherry to the Japanese plum (P. salicina) varieties Abundance and Burbank failed. No symptoms were produced on these two varieties,

and necrotic ring spot was not recovered from them by budding back to

Montmorency.

After the first year of symptom expression, most of the hosts studied by

Moore and Keitt carried the virus without further symptom expression. No

host of necrotic ring spot virus that did not at some time express symptoms

has yet been found, and most hosts carrying necrotic ring spot virus and not

expressing symptoms failed to develop symptoms when inoculated with

necrotic ring spot virus.

Symptoms

Sour cherry.—The initial effect of necrotic ring spot on the Montmorency

variety is a pronounced delayed foliation of individual limbs or entire trees

{iig. 53, A, B). Leaves on affected branches are reduced in size, and before

they unfold they may show hght-green spots and dark rings, which vary in

size from 1 mm. or less up to 5 mm. in diameter and have a water-soaked

appearance (fig. 54, B, C). Partial rings and sometimes concentric rings are

also present. The surface of affected leaves is roughened, and the margins

tend to be wavy {9). In the early stages the ring symptoms are visible by

reflected light only. As the season advances, the affected areas may become

necrotic, fall out, and give a "shredded leaf" effect {iig, 54, A). Symptom

expression usually is limited to the first leaves that unfold; leaves formed

later generally do not show symptoms. In Ontario Berkeley observed that

affected trees have a reduced number of leaves and therefore have a thin

appearance.

Sometimes blossom symptoms also may be present on severely affected

branches. The pedicels may be shortened until they are almost sessile, according to Moore and Keitt and Berkeley. In severe cases, the calyx and corolla

may be twisted and distorted and sometimes chlorotic or necrotic rings or arcs

are present in the sepals. Moore and Keitt noticed also that such severely

affected blossoms ordinarily do not set fruit. Occasionally fruits with smaíl

rings similar to those on the leaves are found on trees showing severe necrotic

ring spot symptoms on the leaves.

The general experience has been that trees severely affected one year show

few or no symptoms in subsequent years except in Ontario where the thinness

of fohage has been characteristic. Usually, if severe symptoms are present

only on certain branches the first year, other branches may show striking

symptoms the next year. In Wisconsin no branches of orchard trees have

been observed to show striking symptoms in more than one year, but certain

nursery trees have shown striking ring symptoms and wavy leaf margins but

no necrosis each year since the initial symptoms appeared in 1941. In a few

trees, however, ring symptoms have persisted for 4 years in Ontario and for 6

years in New York. This variation in symptom expression is indicative of

strains of the virus, or possibly of strains of the host (Montmorency cherry),

or of both.
166 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Figure 53.—A and ß. Branches of Montmorency cherry affected with necrotic ring

spot> she-wing delayed foliation, stunted leaves, and shortened blossom pedicels;

C, comparable healthy branch of Montmorency cherry; D and £, Italian Prune

branches affected with necrotic ring spot, showing necrotic spotting of leaves and

stunting; F, comparable healthy branch of Italian Prune variety.
VIRUS DISEASES OF STONE FRUITS 167

Figure 54.—Montmorency cherry leaves affected with necrotic ring spot, showing

(A) severe necrotic shock symptoms and (ß and C) w^ater-soaked pattern consisting of rings and arcs of rings.
168 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Under greenhouse conditions very severe and striking typical symptoms

were obtained by Moore and Keitt on English Morello sour cherry, beginning

about 10 days after inoculation. The early water-soaked type of rings,

necrotic spotting, and general necrosis, followed by severe leaf shredding,

were present.

Sweet cherry.—In field inoculations of Bing and Black Tartarian sweet

cherry chlorotic rings and chlorotic spotting were obtained on only a part of

the fohage. Some leaf shredding sometimes occurred. In Ontario there was a

tendency for the margins of aííected leaves to be wavy. When inoculations

were made in the greenhouse, symptoms were obtained by Moore and Keitt in

6 to 8 weeks; these symptoms were expressed as chlorotic ring spotting or

chlorotic and necrotic spotting followed by shredding.

In New York symptoms similar to those on Black Tartarian were obtained

on the Eagle variety by Hildebrand. Moore and Keitt reported that under

greenhouse conditions symptoms on Napoleon were about the same as those

on Bing except that there was in addition some killing of spurs. In field

inoculations in Ontario no definite symptoms were obtained on Napoleon

even though transfers back to peach indicated that the necrotic ring spot virus

was present in the inoculated trees. Symptoms obtained by Moore and Keitt

and by Hildebrand on mazzard seedhng were about the same as those on Bing.

Mahaleb cherry.—Chlorotic rings, spots, and patterns were obtained by

Berkeley, Hildebrand, and Moore and Keitt.

Duke cherry.—Very severe and striking typical necrotic ring spot symptoms

similar to those on English Morello occurred on Royal Duke cherry. Most

budded trees of this variety, however, expressed both the ring symptoms and

the necrotic spotting for 2 years after budding with material aííected with

certain forms of necrotic ring spot, according to Moore and Keitt and

Berkeley.

Peach.—Elberta and Rochester trees inoculated in the fall generally had

dead branches above the bud insertion by spring. Often entire trees, especially

those of the Rochester variety, were killed. When branches were not dead

above the point of bud insertion before start of growth in the spring, there

was generally a severe delayed foliation followed by death. Dieback was

common on other branches, and bark splitting and bark cankers often were

present on the trunk and larger branches of inoculated trees. Parts of trees

that survived appeared to be fairly normal by the end of the growing season,

though some mottling of foliage sometimes occurred. According to Berkeley

(8), Hildebrand, and Cation, similar symptoms occurred on peach seedlings.

There was considerable variation as to degree of dieback and killing of peach

resulting from inoculation with necrotic ring spot virus from different

sources. For instance, Berkeley, Hildebrand, and Cation found that virus

from some sources killed entire trees while that from others produced mild

dieback. Hildebrand found that virus from still others produced no killing

or dieback whatever on peach, though it might cause mottling of the leaves

(91), At present this variation in response is considered to be due to strains

of the necrotic ring spot virus or possibly to contamination with other

viruses. By making inoculations under greenhouse conditions on Elberta just

at bud break, Moore and Keitt found that chlorotic and necrotic spotting

occurred shortly after the leaves unfolded and that most affected leaves were

abscised within a period of several weeks. In some cases entire tops of trees

were killed above the point of bud insertion. After the period of initial shock
VIRUS DISEASES OF STONE FRUITS 169

new leaves were for the most part free of symptoms. On the Rochester varietythere was only a faint, chlorotic spotting, but no necrosis or leaf casting.

There was, however, more shoot killing than on Elberta or Halehaven, and

this killing was limited almost entirely to terminals.

ThiTn.—Symptom expression was obtained by Moore and Keitt about 8

weeks after they had budded American plum and the Bradshaw variety of

domestic plum in the greenhouse; small, chlorotic or necrotic flecks which

tended to follow the larger veins appeared. According to Berkeley, numerous,

small, necrotic spots or flecks appeared on unfolding leaves the year following

inoculation of Italian Prune (fig. 53, D, E). Affected branches showed slight

delay in foliation, and affected trees outgrew the symptoms and later appeared

to be normal.

Fin cherry.—In a greenhouse with a constant temperature of approximately

21° C. at Wisconsin and under greenhouse conditions in Ontario, symptoms

on pin cherry consisted of severe necrosis and shredding of leaf tissue. Recovery after initial shock was striking in this species.

Ornamentals.—-In the stone-fruit-virus greenhouse at Wisconsin (temperature range at night 13° to 15° C.) no symptoms were obtained on P. besseyi,

and only mild symptoms occurred on P. ptimila and P. virginiana. In greenhouses with approximately constant day and night temperatures of 24° or 28°

striking chlorotic ring spots or line patterns occurred on all three species. In

addition, P. besseyi showed chlorotic spotting, leaf roughening, and some

necrotic spotting, and P. pumila showed necrotic spotting, and shredding

{164).

Transmission

The disease can be transmitted by any grafting method. Symptoms

generally show early in the spring following fall budding. In one case

symptoms were observed by Berkeley in September on the new leaf growth

of the Italian Prune variety bud-inoculated in August. The Wisconsin

investigators (162) successfully transmitted necrotic ring spot by mechanical

means from sour cherry to cucumber.

Incubation Period

In greenhouse work with stocks and scions just about to break dormancy,

symptoms were obtained by Moore and Keitt in from 5 days on Montmorency

sour cherry to 8 weeks on Bradshaw and American plum. In Hildebrand's

tests on sour cherry the incubation period ranged from 10 days to 5 weeks

and on sweet cherry from 2 to 6 weeks. On Italian Prune and peach

seedlings the incubation period was 2 ^ to 5 weeks, according to Berkeley.

Thermal Relationships

Necrotic ring spot has been transmitted, with the expression of symptoms,

from Montmorency to Montmorency sour cherry over a temperature range of

10° to 28° C, with much more necrosis and shredding of leaves at the higher

temperatures. The best temperature for expression of both rings and necrosis

on Montmorency was 20° to 24°. Killing of entire terminals and spurs was

common at 28°. Studies on inactivation of the virus in Montmorency bud

sticks indicate that a heat treatment sufficient to inactivate the virus will kill

the cherry tissue (161), Necrotic ring spot was transmitted by Moore and

Keitt from bud sticks 6 inches long and 2.7 to 3.0 mm. in diameter that had

received a heat treatment of 50° for 22 minutes.

Control Measures

Cherry trees to be used as sources of budwood should first be indexed on
170 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

peach or virus-free Montmorency sour cherry in order to ascertain whether

the necrotic ring spot virus is present. Buds from healthy trees only should

be used for top-working or for general propagation purposes.

In some States and in Ontario, Montmorency sour cherry nursery stock free

from the necrotic ring spot virus and the cherry yellows virus is now, or will

soon be, available. Such nursery stock is recommended for planting purposes.

Remarks

The fact that Montmorency sour cherry is often a symptomless carrier of

the necrotic ring spot virus makes the problem of evaluating the economic

importance of necrotic ring spot very difficult. Moreover, the possible effects

of the necrotic ring spot virus on symptom expression of sour cherry yellows

and on yield from trees affected with yellows are not known at present, since

a virus of the necrotic ring spot type or a necrotic ring spot factor has been

associated with yellows from all sources investigated to date. No one has yet

been able to separate the necrotic ring spot factor from the yellows complex.

The problem of their detection in nursery stock has been approached in

two ways. In Wisconsin (166) reliance has been placed chiefly on the reaction

of disease-free Montmorency sour cherry to inoculation, whereas in New York

(95), Michigan, and Ontario peach seedlings have been used as indicators. The

latter procedure has been used on the grounds that the peach when not cut

back reacts to necrotic ring spot virus with delayed foliation, varying degrees

of dieback, and necrotic spotting of leaves and to sour cherry yellows virus

with varying degrees of rosetting occasioned by shortened internodes in

addition to the afore-mentioned symptoms associated with necrotic ring spot.
VIRUS DISEASES OF PLUM AND PRUNE

PRUNE DWARF

By E. M. HILDEBRAND, T. B, LOTT, and R. S. WILLISON

Other Common Names of the Disease

Prune mosaic, Fellenberg mosaic, willows, and shoestring of Italian Prune.

Names of the Causal Virus

Nanus pruni Holmes; Prunus virus 6 (Thomas and Hildebrand) Smith.

Geographic Distribution

Prune dwarf is known only in New York and in Ontario and British

Columbia, Canada.

Economic Importance

Prune dwarf renders Italian Prune (Fellenberg) unproductive, but it is of

minor importance because of its limited distribution. Since two strains of

the virus occur on sour and sweet cherries in New York (85, 92) and others

on sweet cherry in Ontario (7, 246), the economic importance may prove

greater than is now realized.

Host Range

Characteristic strap-shaped leaves are produced on Italian Prune and

Lombard plum (Prunus doutestica) ; and various symptoms are produced on

peach (P. pérsica) seedlings and varieties and on mahaleb cherry (P. mahaleb)

rootstock. The virus may occur without causing symptoms in damson plum

(P. insititia) ; in domestica plum (P. domestica) varieties Bradshaw, Reine

Claude, and German Prune; in Japanese plum (P. salicina) variety Abundance;

in Shiro hybrid plum; in myrobalan plum (P. cerasifera) rootstock; in sweet

cherry (P. avium) varieties Napoleon (Royal Ann), Black Tartarian, Eagle,

and Elkhorn; in sour cherry (P. cerasus) variety Montmorency; and in apricot

(P. armeniaca) variety Niagara. The disease has been found in nature on

Bradshaw and damson plums, Italian Prune, and sweet and sour cherries. The

remainder of the hosts have been experimentally infected.

Symptoms

Pluin.—The affected leaves of the Italian Prune variety (fig. 5 5, A) are

small, narrow, straplike, rugose, somewhat thickened, distorted, glazed,

frequently emarginate, and sometimes marbled with an obscure mosaic mottle

{232). The onset of the disease on Italian Prune is marked by a relatively mild

chlorosis (rings and mottling) on normal-sized leaves. Leaves formed later on

the same tree are smaller and spindly. Terminal growth is reduced, and internodes are shortened. Unless the trees are small and young, they do not usually

show symptoms over the entire tree. In the first year after inoculation the

diseased shoots may be scattered among branches that appear normal. Later

occasional healthy shoots may occur on trees completely and severely affected.

Diseased trees blossom well, but the pistils are aborted and few fruits mature.

The petals of affected flowers are frequently narrow and distorted (S5, 232),

Fruits on diseased trees are often larger than normal and of excellent quality.

Willison {246) obtained several strains of the virus from damson plum,

171
172 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Bradshaw plum, sweet cherry, and sour cherry. These sources vary in their

virulence and effect on Italian Prune and in their rate of spread through

the tree.

Figure 55.—A, Italian Prune branch affected "with prune d"warf, sho'wing strap-shaped

leaves; B, peach shoot afiected ^th the same disease, sho-wing short internodes and

spikelike apical leaves.

Foliage symptoms on Lombard plum are similar to, but less severe than,

those described for Italian Prune. There may be mild, chlorotic flecking of

early leaves, waviness of the laminae, and dwarfing and semirosetting of the

shoots (^5, 246). Reduction in yield is shght (S5). With the milder virus

strains there seems to be a tendency toward localization of the disease in the

vicinity of the point of inoculation (246).

Other plum varieties may show transient symptoms such as mild mottle,

chlorotic spotting, ring patterns, and delayed foliation in the early stages of

infection; apparently they recover later, though in some instances a slight

dwarfing effect may persist.

Peach.—Only minor differences were noted in the symptom expressions of

individual virus strains on peach varieties. However, some strains caused more

severe symptoms than others. Prune dwarf on peach is characterized by a

slight delay in foliation, wavy leaf margins, and a tendency for the leaves to

roll upward and inward from their margins and to be stiff and erect, pointing

upward. Dwarfing of shoots and shortening of internodes (fig. 55, B) sometimes resulted in loose rosettes, but the degree of dwarfing and shortening

varied with the different strains of the virus. Leaves produced early in the

season were sometimes marked by transient mottles, chlorotic spotting, feathery

mottled patterns, or confluent rings. Superficial bark necrosis was noted

with some strains. Milder strains of the virus produced slight symptoms that

usually became masked after the initial stage. Lott observed that symptoms

persist on peach for 2 or 3 years. Some peach trees may show very little effect.
VIRUS DISEASES OF STONE FRUITS 173

Cherry.—Symptoms on sweet cherry varieties consisted mainly of rings of

varying size and intensity, of line or oak-leaf patterns, and of mottling on

early-spring leaves. Ordinarily the symptoms were largely masked after the

first season of infection. Field data on yield indicated that the crop is definitely

reduced by prune dwarf.

In early stages of infection of the Montmorency variety of sour cherry

there was a tendency for delayed foliation (246). Also some early leaves

showed various degrees of ring spotting, necrosis, and flecking. These symptoms

were most prominent on Montmorency inoculated with a mixture of prune

dwarf and line pattern viruses. Late in the season the symptoms sometimes

entirely disappeared. They seldom recurred subsequently. In New York one

strain of prune dwarf virus from a yellows-aííected cherry tree sometimes

induced symptoms simulating yellows when passed through Italian Prune and

returned to Montmorency cherry. In Ontario a strain of pure prune dwarf

virus contaminated with the line pattern virus caused coarse line pattern

symptoms later associated with necrotic spots and streaks on a considerable

number of leaves scattered through a Montmorency cherry tree. The

symptoms recurred in mid-June; affected leaves were usually cast.

The reaction of mahaleb cherry seedlings to each strain was variable. Some

seedlings were symptomless and others exhibited mottles, lines, coarse rings,

and oak-leaf patterns on leaves produced in spring and late summer (246).

Apricot.—On apricot no leaf symptoms beyond faint mottling were

observed, but foliation was sometimes delayed in the spring and some reduction

in vigor sometimes occurred (246),

Diagnostic or Unusual Characteristics

The dwarfed, irregular, strap-shaped leaves of Italian Prune and Lombard

plums and the wavy, stiff leaves and shortened internodes of peach are

important diagnostic characters. The occurrence of occasional normal twig

growth on diseased branches and the slow movement of the virus in plums

are also significant. In Ontario the disease occurs on Italian Prune variety

only when that variety has been top-worked on damson plum, indicating that

the damson is a carrier. According to Hildebrand, thermal inactivation of

the prune dwarf virus has an end point at 50° C. in 20 to 22 minutes.

Transmission

The various strains of prune dwarf virus are readily transmitted by budding

and grafting. The insect vector is not known though limited natural

spread has been observed in New York (85). Lott transmitted a strain of

the virus from Napoleon sweet cherry which produced very slight symptoms

on Italian Prune soon after grafting when transmission was made direct from

cherry to Italian Prune or through peach.

Incubation Period

When inoculation occurs early in the growing season, the incubation period

may be as short as 5 weeks on ItaHan Prune. When trees are inoculated in

the fall, the symptoms usually do not appear until the following spring.

Symptom development may be delayed until the second growing season.

When seedling peaches are inoculated by budding and cut back to the infective

bud, symptoms of chlorosis may develop within 1 month on the first new

growth of the seedling.

Control Measures

Roguing of affected Italian Prune is recommended as such trees are

commercially unprofitable. When Italian Prune is to be on other, top-worked
174 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

plum varieties, it is desirable that these varieties first be indexed to determine

whether the virus is present and that infected ones be discarded. Indexing

can be done by placing buds from the trees in question on healthy susceptible

nursery trees or by placing healthy Italian Prune scions on the trees to be

top-worked.

Remarks

In New York inoculum containing strain 1 of sour cherry yellows virus

induced symptoms of prune dwarf on Italian Prune and Lombard pkim

varieties and also a rosette on peach, as did a mixture of cherry yellows and

necrotic ring spot viruses in Ontario* Willison has observed no definite

instances of yellows symptoms on Montmorency sour cherry inoculated with

prune dwarf virus from naturally affected Italian Prune. The symptoms of

prune dwarf on peach resemble those of rosette mosaic, but the relationship of

the respective caiisal viruses has not yet been demonstrated. The prune dwarf

virus has been found in sweet cherry associated with the tatter leaf virus and

in Italian Prune associated with the line pattern virus. Though the reaction

of peach to the prune dwarf virus strains worked with in Ontario indicated

that these strains were not contaminated with necrotic ring spot virus, there

is no reason why this combination of viruses should not occur in nature.

Indexing trials indicate that prune dwarf may be distributed in masked form

in sweet cherry. It is of interest that the thermal-inactivation point of the

rosette mosaic virus is near if not identical with that of prune dwarf virus:

namely, an exposure of 20 to 22 minutes at 50^ C.
PRUNE DIAMOND CANKER

By RALPH E. SMITH and H. EARL THOMAS

Name of the Causal Virus

Prune diamond canker virus.

History and Geographic Distribution

The disease was noted only occasionally before 1915. Trees planted in the

decade after that year often developed a rather high eventual incidence of

disease, particularly in the Santa Clara and Napa Valleys of California. It

seems now that the prevalence of the disease in the prune-growing districts of

the State is related chiefly or entirely to the accidental dispersal of the virus

in nursery stock (4). At any rate the disease is rare in the Sacramento and

San Joaquin Valleys and probably is unrecognized outside the State.

Economic Importance

Affected trees undergo an initial seemingly stimulating effect. This is

followed by a slow decline in vigor and fruitfulness hastened by secondary

causes. Eventually diseased trees become worthless or nearly so. The widespread occurrence of the disease expressed and in the incubation stage has been

the cause of substantial losses in French (Agen) prune orchards and will

continue to be for some years to come.

Host Range and Varietal Susceptibility

Symptoms of diamond canker are expressed only on the French (Agen)

prune (Primus doviestica), The disease appears to be more prevalent in

certain horticultural selections of French prune than in average trees of the

variety. Some of these selections have become widely planted. Typical

cankers developed on the tops grown from diseased French prune scions

grafted on apricot (P. armeniaca), almond (P. amygdalus), peach (P. pérsica),

myrobalan plum (P. cerasifera), and other rootstocks but without symptoms

on the rootstocks. In a small percentage of cases the virus passed from

diseased scions of French prune grafted on one side of a non-symptom-producing stock to previously healthy arms of a French prune grafted on the other

side (214).

Symptoms

The name "diamond canker" arose from the fact that in some cases the

bark becomes thickened and roughened in a more or less diamond-shaped area

often around a wound (212). The wood may or may not be exposed. In

other cases the bark may be roughened generally over the older parts of trees

(ñg. 56). Slight roughening is sometimes seen on bark only a year or so old.

It is not known whether the variations are due to strains of the virus, to

different susceptibility of the prune clones, or to both. No fruit or leaf

symptoms have been recognized.

Transmission and Incubation Period

Healthy scions grafted on affected trees may show symptoms in 2 years,

but often do not do so until several years later (214). For this and other

reasons there is some uncertainty whether there is natural spread in orchards.

The evidence suggests that most if not all dissemination has been by buds and

scions from shoots too young to show recognizable symptoms.

175
176 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

ïigure y 6.—French (Agen) prune affected with diamond canker.

Control Measures

Since there is little evidence of spread of the virus causing diamond

canker from tree to tree in the orchard, the disease should be eliminated by

removal of diseased trees as they become unproductive and replacing them

with nursery stock propagated from trees known to be free from the virus.

Remarks

It is suggested that prune diamond canker is similar to psorosis of citrus

(72), but it is not known whether the causal virus of diamond canker like

that of psorosis is systemic and gives rise to a localized form that causes

localized cankers. In any event the diamond canker virus can be recovered

from symptomless parts of an affected tree.
LINE PATTERN

By DONALD CATION, G. H. BERKELEY, J, A, MILBRATH,

R. S. WiLi.isoN, and S. M, ZELLEPV

Other Common Namies of the Disease

Shiro line pattern, peach line pattern, and banded chlorosis of oriental

flowering cherry.

Names of the Causal Virus

Marmor lineopicttun was applied by Cation to line pattern of plum and

M. pallidolimbaHis was applied by Zeller and Milbrath to banded chlorosis of

oriental flowering cherry. Ultimately Zeller and Milbrath considered banded

chlorosis closely related to or identical with line pattern. Therefore, by

priority, M. lineopicttun Cation is now the recognized name.

History and Geographic Distribution

Line pattern has been reported on plum in the Niagara district of Ontario,

Canada, {7, 247) and in Michigan (47), New York (S5), and Kentucky

(242) and as banded chlorosis on oriental flowering cherry in Washington and

Oregon (261). The disease has been identified on plum nursery stock grown

in Ohio (47), Kentucky (242), Oregon, and Washington (261), Similar

diseases have been reported in California (23 3) and Europe (2, 3, 53). Line

pattern is probably widely distributed at least throEighout the United States.

Symptoms of line pattern on plum and peach were first reported by Valleau

(242). He did not assign a name to the disease, and there is the possibility

that in some instances he was working with a mixture of viruses (47),

Economic Importance

Line pattern on most varieties of plum and peach appears to be of negligible

importance, and on oriental flowering cherry damage is limited to unsightly

foliage. There are indications, however, that the severity of symptoms

increases when the line pattern virus is combined with other viruses and a

complex infection results.

Host Range and Varietal Susceptibility

Line pattern occurs in nature frequently on Japanese plum (T^rumis

salicina) varieties Red June and Abundance and on oriental flowering cherries

(P. serrulata) varieties Amanogawa, Shirotae (Mount Fuji), Naden,^^

Kwanzan, and Temari and to a less extent on peach (P. pérsica) seedlings.

The following species and varieties have been artificially infected: Peach

varieties Elberta, J. H. Hale, Rochester, and Carman and seedlings; Japanese

plum varieties Abundance and Red June; the hybrid plums Shiro and First;

domestica plum (P. domestica) varieties Italian Prune, Early Golden Drop,

German Prune, Imperial Gage, Reine Claude, Lombard, and Grand Duke;

myrobalan plum (P. cerasifera) seedlings; sweet cherry (P. avinm) varieties

Black Tartarian and Napoleon (Royal Ann) ; mazzard (P. avinm) seedlings;

sour cherry (P. cerasus) variety Montmorency; and mahaleb cherry (P. maba-

''" Tlie varietal name "Naden," as used in this paper, refers to an apparent liortictiltural

strain o£ the variety Kwanzan. It should be noted also that the name "Naden" is sometimes

applied to the variety Takasago (P. skboldii),

8517930—51—15

177
178 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

leb) seedlings. On these artificiaÜy infected hosts the symptoms varied in

intensity. Apricot (P. armeniaca) variety Niagara appeared to be a symptomless host.

Symptoms

The symptoms are almost invariably confined to the leaves emerging in

the spring when the daily mean temperatures are below 55° to 60° F.

(12.8° to 15.6° C), and they persist on these leaves throughout the season.

Therefore, later in the summer most of the leaves on infected trees are

symptomless.

Fhivi.—Commercial varieties of plum were very variable in symptom

expression. Patterns on leaves usually consisted of lines, bands, and oak-leaf

patterns. Vein banding was observed by Willison and Berkeley. In 1945

Zeller and Milbrath noted small rings in addition to other symptoms.

On Shiro plum {iig. 57, A) and myrobalan plum seedlings (fig. 5 8, D) the

patterns were conspicuously yellow or yellow green in the spring and became

a vivid creamy white early in the summer {247).

On Abundance plum the patterns resembled those on Shiro, but were less

conspicuous and more transient (247), The symptoms consisted of chlorotic

rings, spots, and line patterns bordered with a white to bright-golden band,

which was more pronounced for line pattern than for banded chlorosis,

according to Zeller and Milbrath. Infected Abundance bore normal crops

of good-quality fruit (47).

On Italian Prune, Reine Claude, and First plums the patterns were of a

very faint oak-leaf type; on Italian Prune they were absent in some seasons.

On German Prune and Grand Duke plums fine, irregular, yellowish lines

predominated (247). Willison and Berkeley found that Imperial Gage and

Early Golden Drop plums and some myrobalan plum seedlings carried the virus

without symptoms. Other myrobalan plum seedlings showed a golden-net

pattern bordering the veins and veinlets, according to Zeller and Milbrath.

On Lombard plum only a few leaves were affected. On these, Willison and

Berkeley noted faint markings of the Shiro type, but the more characteristic

symptom was a regular, chlorotic, and eventually necrotic, line outlining the

marginal triangular section on the lamina and usually distorting the leaf.

Peach.—No differential reaction of peach varieties to line pattern was

detected by Willison. The characteristic symptom was a fine, irregular, wavy

band on each half of the lamina, usually forming a symmetrical pattern (fig.

57, B). Some leaves were marked with a network of fine lines, or a golden-net

pattern, fine confluent rings, vein banding, or an oak-leaf pattern, or both of

the last two. Markings on peach leaves were generally pale green or more

rarely yellow green, and usually they disappeared in the course of the summer.

The number of affected leaves and the predominant type of symptom varied in

outline from year to year in response to the temperature conditions in the

spring (247). Similar line patterns and ring spots were produced on J. Fi. Hale

peach inoculated by Milbrath and Zeller with buds from trees affected with

line pattern or with banded chlorosis.

Soar cherry.—On Montmorency sour cherry the symptoms in the early

stages of infection were inconspicuous, pale-green bands, spots, and coarse

rings, and a few necrotic spots also were present. In the following year

sharply defined lines (ii^. ^^^ B) did not appear until early June. These lines

were sometimes chlorotic, but more commonly they appeared as watermarks

seen best by transmitted light, according to Willison and Berkeley.
VIRUS DISEASES OF STONE FRUITS 17^

Figure 57,—A, Shiro plum leaves affected with line pattern; B, peach leaves afiected

Tvith the same disease.
180 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Mahaleb cherry.—On mahaleb cherry seedlings symptoms consisted of oakleaf patterns and coarse lines and rings, sometimes darker and sometimes paler

than the rest of the leaf (fig. 5 8, C). Short, narrow yellow bands along the

larger veins are of diagnostic value. In these areas the veins, and frequently

part of the yellow-band tissue, eventually become necrotic and either split or

drop out. The severity of symptoms varied with the individual trees {247).

figure 58.—A, Leaf of Amanogawa oriental flowering cherry affected with line pattern (banded chlorosis). B—D, Leaves of various species affected with the same

disease: By Montmorency cherry; C, mahaleb cherry; D, myrobaian plum.
VIRUS DISEASES OF STONE FRUITS 181

Milbrath and Zeller found that the Michigan strain of the Une pattern virus

produced a pronounced golden blotch mottle with some ring spots, whereas

the Oregon strain from Amanogawa oriental flowering cherry produced a

banded oak-leaf pattern on some leaves and banded circular spots or irregular

line patterns on others. The majority of the leaves showed no symptoms.

Sweet cherry.—On Napoleon and Black Tartarian cherries the virus caused

similar symptoms, according to Willison and Berkeley. Symptoms were

divided into two groups. The first comprised tiny fine rings, larger coarser

rings, and faint oak-leaf patterns, which were more or less transient. The

second group consisted of persistent watermark lines and more conspicuous

yellow and later creamy-white lines up to 1 mm. in width. These lines formed

striking irregular patterns, usually occupying less than a quarter of the leaf

surface.

According to Zeller and Milbrath, on young foliage of Bing and Black

Republican cherries line pattern virus caused faint line pattern symptoms

which later became pronounced, whereas inoculations with buds from bandedchlorosis-affected trees caused well-formed, banded oak-leaf patterns on young

foliage of Bing, Lambert, and Napoleon cherries. As these trees became older

they showed chlorotic mottle.

Milbrath and Zeller found that mazzard cherry seedlings inoculated with

buds from banded-chlorosis-affected trees vary greatly in symptom expression.

Some seedlings showed a well-formed, banded oak-leaf pattern; others showed

an irregular chlorotic or red mottling. In some seedlings tissues with these

various patterns became necrotic and fell out, and then the leaves had a lacy

appearance. The line pattern virus produced patterns similar in outline, but

different in that the banding was of a bright-golden color.

Oriental flowering cherry,—On all affected varieties of oriental flowering

cherries (Amanogawa, Shirotae, Naden, Kwanzan, and Temari) on which

Zeller and Milbrath found the disease, the symptoms were similar {iig. 5 8, A).

The borders were faintly chlorotic to pronounced golden or white. The

patterns were sometimes made up of large rings, but more often they were of

an oak-leaf type. The line pattern virus caused similar symptoms on Amanogawa, but the lines were less pronounced.

Diagnostic or Unusual Characteristics

Willison {247) considered as diagnostic for line pattern the striking yellow

to white patterns on Shiro and myrobalan plums and Napoleon and Black

Tartarian sweet cherries, the pale-green lines on peach, and the watermark

lines on sour cherry. In comparing banded chlorosis with line pattern on

several hosts, Zeller and Milbrath found the symptoms of banded chlorosis

more pronounced than those of line pattern on the Amanogawa variety of

flowering cherry and Bing and Black Republican sweet cherries and less pronounced on mahaleb and mazzard cherry seedlings and Abundance plum.

Symptoms of the two diseases appeared identical on Shiro plum and J. H. Hale

peach.

Of special interest is the effect of temperature on symptom expression,

symptoms occurring only on leaves developed in the spring during cool

weather. Differences in the varietal reaction of plums is also noteworthy,

according to Willison and Berkeley.

Transmission

Transmission is easily effected by budding and bark-patch grafting. Evidence of natural dissemination was observed at East Lansing, Mich., {47) and
182 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

in an orchard in Ontario by Willison and Berkeley. From these few observations there were indications that the vector is comparatively rare and the dispersion range is short.

Incubation Period

Trees budded in the summer produce affected foliage the following spring.

Cation observed symptoms 6 weeks after inoculation under low-temperature

conditions in the greenhouse in one trial in 1945.

Control Measures

It is doubtful whether roguing should be recommended. Use of disease-free

stock and scion material for nursery propagation and top-working plum

varieties is indicated by experiments of Willison and Berkeley and of Zeller

and Milbrath.

Remarks

The combination of line pattern virus with the prune dwarf virus increases

the virulence of prune dwarf in some hosts and of line pattern in others. The

line pattern virus or close relatives seem to be widely distributed on stone fruits

in various parts of the world (247). According to Zeller and Milbrath, banded

chlorosis of oriental flowering cherry in western United States is closely related

to, if not identical with, line pattern as found in the East on Japanese plum.

The presence of this disease on ornamental oriental flowering cherry varieties

indicates that it may have been imported from Japan, although as far as is

known it has not been recognized in that country.
PLUM WHITE SPOT

By H. EARL THOMAS and T. E. RAWLINS

Other Common Names of the Disease

Santa Rosa plum mosaic.

Name of the Causal Virus

Aegrescit medendo Thomas and Rawlins.

Geographic Distribution

Plum white spot is known in Santa Cruz County, Calif., (233) and in

orchards near Prosser, Wash. Distribution of this disease is probably wider,

but the mosaics of plums are still to be distinguished clearly.

Economic Importance

This disease is probably of slight economic importance. The affected

orchard first brought to attention of the authors was found to be more

seriously damaged by other factors. Trees affected with plum white spot virus

growing in good soil are not greatly impaired in vigor.

Figure 59.—Leaves of Santa Rosa plum naturally affected with plum white spot.

183
184 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Host Range

Only the Santa Rosa plum (Prunus salicina) has been seen naturally

affected, and other species have not been tested.

Symptoms

Symptoms consist of small, pale=yellow to paper-white spots tending to be

aggregated toward the tip of the leaf (fig. 59).

Transmission

The disease is transmitted by grafting.
STANDARD PRUNE CONSTRICTING MOSAIC

By H. EARL THOMAS and T. E. RAWLINS

Other Common Names of the Disease

Standard prune mosaic.

Name of the Causal Virus

Vtdnus immcdicabile Thomas and Rawlins.

Geographic Distribution

Standard prune constricting mosaic is known in one orchard in Butte

County, Calif., {23}) and has been observed in one lot of nursery stock

grown in central California.

Economic Importance

Eighty percent or more of the trees are infected in the one orchard known

to be involved and the reduction in tree vigor seems to be considerable, but

because of the limited known distribution the threat is potential rather than

actual.

Host Range and Varietal Susceptibility

Standard prune {Primus domestica) is naturally infected. Peach (P.

pérsica) has been infected by inoculation. No symptoms developed on Sugar

prune following inoculation by inarching with affected Standard prune.

Symptoms

Few to many chlorotic spots develop in the leaf blade of Standard prunes.

These are often Viii to VH inch in diameter and somewhat vague in outline.

A distinctive feature is the concentration of the spots in a band across the tip

Figure 60.—Leaves of Standard prune affected with constricting mosaic,

185
186 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

half of the leaf blade; often necrosis follows, and all but the midvein in that

area drops out (ñg. 60). The symptoms are more conspicuous in warm

weather than in cool. Symptoms on inoculated peach seedhngs vary from

indefinite mottling to clear-cut patterns of hnes and rings. The damage to

peach seems to be slight.

Transmission

Transmission has been effected by grafting.

Incubation Period

Plants inoculated in October and rested in midwinter developed symptoms

in February of the following year.

Control Measures

The use of healthy buds of the prune for propagation of nursery stock is

indicated.
RING POX OF APRICOT

By E. W. BoDiNE and E. L. REEVES

Other Common Names of the Disease

Ring pox has been called apricot ring spot in Colorado, and in Washington

it is locally referred to as apricot pox and ring pox. Since the name "ring spot"

was applied in 1941 to a virus disease of stone fruits affecting peach (62), the

name "ring pox" proposed by Reeves (184) for this virus disease of apricots is

preferred.

Name of the Causal Virus

Ring pox virus.

History and Geographic Distribution

Bodine and Kreutzer (3 8) observed this virus disease on apricots in Colorado

in 1935, but the disease was described for the first time in 1942 under the name

*'ring spot" (3 8, 40), Reeves (184) noted its occurrence in Washington in

1939 and established its virus nature in 1941.

Economic Importance

Several hundred apricot trees affected with ring pox were removed in Mesa

County, Colo., from 1936 to 1940. Since then, however, relatively few new

cases have been observed. Ring pox has been reported from the Wenatchee

and Yakima districts in Washington, but is considered of general minor

importance in the State because of its low incidence. However, ring pox is

viewed with concern since there has been evidence of field spread in both

Yakima and Wenatchee Valley orchards. Most known diseased trees were

removed from Washington orchards by 1945.

Host Range

So far as is known the virus of ring pox has been reported only on apricot

(Prtinus armeniaca). Orchard trees of the Montgamet, Wenatchee Moorpark,

and Tilton varieties have been found affected.

Symptoms

Both the leaves and the fruits of affected trees exhibit symptoms of the

disease. Reeves (184) reported some variation in symptoms on different

varieties. In general the leaves of the Wenatchee Moorpark and Montgamet

varieties develop irregular ring and angular spots and marked clearing of the

principal veins, while those of the Tilton variety exhibit chlorotic areas. As

the season progresses, the discolored tissues frequently become necrotic and

crumble away, giving the leaves a ragged and shot-hole appearance. Under

Colorado conditions developing fruits appear normal until approximately 2

weeks prior to ripening. After this time, the fruits exhibit protuberances,

which often give individual fruits a bumpy appearance. During the ripening

process the affected fruits fill out and tend to lose their bumpy appearance, but

develop reddish-brown necrotic blotches, or ring spots (pi. 22). These discolorations normally extend into the flesh of the fruit. On ripe fruits with

such symptoms cracks often develop in the discolored areas. On any thoroughly diseased limb all fruits show symptoms such as those just described.

Under Washington conditions, recognizable fruit symptoms are apparent at

187
188 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

least 6 weeks prior to harvest maturity and many of the fruits drop before

they become ripe.

Transmission

Transmission has been effected through inoculation by bud and scion

grafting only.

Incubation Period

Bodine and Kreutzer (3 8) reported an incubation period of approximately

2 years in the Montgamet variety. Reeves {184) inserted diseased buds into a

20-year-old Tilton tree in July 1941, and all fruits on the tree exhibited

symptoms in May 1942.

Control Measures

Trees affected with ring pox are rendered commercially worthless and it is

suggested that they be removed. Care should be taken in infected districts

to ascertain that budwood sources are free of the disease.
VIRUS DISEASES OF ALMOND

ALMOND CALICO

By H. EARL THOMAS and T. E. RAWLINS

Name of the Causal Virus

Arcana caelestia Thomas and Rawlins.

Geographic Distribution

Calico is widely scattered and is probably general in many almond orchards

in California, but there are at least four mosaic-type diseases of almond in the

State still to be sorted out.

Economic Importance

No reduction in yield has been noted on trees showing well-defined leaf

symptoms. The original tree from which the disease was described {2}}) was

found to be affected also by another and more destructive virus.

Host Range

Natural infection has been found on almond (Pnnms amygdahis). By

inoculation, peach (P. pérsica) and mazzard cherry (P. avium) seedlings have

been infected.

Symptoms

Almond.—Affected trees show variable amounts of fohage with chlorotic

blotches in the leaf blade without pattern and with httle distortion (fig. 61).

Figure 61.—Almond leaves affected with almond calico.

Peach.—Leaves on inoculated seedling peach trees slowly developed mediumlarge pale-yellow blotches without definite pattern or marked distortion.

Cherry.—Leaves on inoculated mazzard cherry seedlings produced chlorotic

blotches or fairly definite lines with or without distortion; the symptoms were

so variable as to suggest infection with a mixture of viruses.

189
190 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Transmission

The disease is transmitted by grafting.

Incubation Period

Depending on the stage of growth of the host, the incubation period on

aimond varied from 7 weeks to 19 months.
DRAKE ALMOND BUD FAILURE

By E. E. WILSON and GILBERT L. STOUT

Other Common Names of the Disease

None.

Name of the Causal Virus

Drake almond bud failure virus.

Geographic Distribution

So far the disease has been found only in three orchards located, respectively,

in Yolo, Colusa, and Sacramento Counties, Calif.

Economic Importance

Because of its low incidence the disease causes negligible loss to the almond

industry. In the one orchard where it is most prevalent, however, it has

rendered a number of trees nonfruitful.

Host Range

The Drake variety of almond {Prtmiis avtygdahis) is the only one so far

found naturally affected. The Nonpareil variety is affected when artificially

inoculated.

Symptoms

The failure of blossom and leaf buds to grow is the basic and characteristic

symptom of the disease. All or most of the buds on a twig may fail to grow.

When all buds fail, the twig remains alive during the spring but eventually

dies. When the terminal bud is among those failing to grow, the twig dies

back to the uppermost live lateral bud. Most or all lateral buds that grow

develop into shoots rather than part into shoots and part into spurs {ñg. 61),

Thus, after a succession of bud failures, there is produced a limb with many

branches, some of which are dead at the ends and none of which bear a full

complement of leaves {iig. 63, A). Certain affected shoots taper somewhat

more than normal ones, being thicker at the base but decreasing to an

approximately normal diameter at the tip. The affected shoots not infrequently appear to be shorter than normal ones, and the leaves are more closely

spaced.

Leaves on affected trees are slightly darker green and possibly somewhat

larger than those on nonaffected trees. They appear to stand rigidly upright,

not, as on nonaflfected trees, bending away from the twig. Affected trees

retain their foliage later in the fall than nonaffected ones. In fact some leaves

may remain on the tips of the shoots until spring.

AfiFected trees blossom much less profusely than nonaffected ones, but the

flowers are normal in shape, size, and color. The fruits, though normal in

color, are few in number and frequently misshapen, the hulls being thicker

than those on nonaffected trees and somewhat bumpy instead of smooth.

Transmission and Incubation Period

Drake almond bud failure has been transmitted to the Drake and Nonpareil

varieties of almond by grafting scions from affected Drake trees onto nonaffected trees. Growth from the affected Drake scions showed symptoms of

bud failure in 2 or 3 years. Severe bud failure developed on the inoculated

191
192 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Figure 62,—End of a Drake almond branch, show^ing the effect of 3 years of bud

failure. On the four shoots produced the previous year, only two terminal leaf

buds, three lateral leaf buds, and one lateral blossom bud grew*
VIRUS DISEASES OF STONE FRUITS 193

Figure 63.—Ay Branches of a Drake almond tree affected with Drake almond bud

failure showing rigid, upright leaves, bare twigs, and absence of fruit; B, comparable unaffected branches showing normal foliage and a good crop of fruit.

891793°—51—16
194 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

stock within 2 or 3 years. Within 4 years the trees were sparse in foliage and

nonfruitful.

Remarks

A bud failure disorder with symptoms similar in certain respects to those on

Drake occurs on Nonpareil, Peerless, and Jordanolo varieties in nature. Inasmuch as this disorder has not been transmitted by methods employed for the

Drake disorder, it has been provisionally classified as nontransmissible.

Formerly Drake almond bud failure was described with the nontransmissible

almond bud failure {229, 251),
VIRUSLIKE DISEASES NOT PROVED

TRANSMISSIBLE

SWEET CHERRY CRINKLE LEAF

By C. F. KiNMAN, W. B. HE^3írITT, T. B. LoTT, G. L. PHILP, E. L. REEVES,

R. S. WiLLisoN, and S. M. ZELLER

Names of the Disease

The name ''crinkle leaf" has become of such wide use among growers that,

although it does not describe the disease adequately, it has been adopted.

Among the names that have been applied to affected trees are ''curly-leaf trees,"

"wild trees," "male trees," "red bud," and "unproductive cherry."

Causal Agent

The predominance of evidence indicates that crinkle leaf is not transmissible

by the visual methods used for virus diseases and that it probably is due to a

genetic bud variation.

History and Geographic Distribution

Crinkle leaf was first described by Kinman {127) under the name "unproductive cherry" in 193 0. He reported its common occurrence on the Black

Tartarian variety in many parts of California and Oregon. Subsequent reports

and surveys showed the trouble to be so common on Black Tartarian that its

known occurrence coincides with the distribution of this cherry variety in all

the major sweet cherry sections of western United States and western Canada.

Economic Importance

Crinkle leaf is the cause of great monetary loss in orchards of affected

varieties every year. Planting of affected nursery stock results in multiple loss

including the original cost of the nursery trees and the cost of maintaining

them in the orchard until they have been proved to be worthless. Surveys in

Washington, reported by Coe (66), showed that 4.1 percent of all the bearing

sweet cherry trees in the State and 6.4 percent of the symptom-expressing

varieties were affected with either crinkle leaf or deep suture. Bing and Black

Tartarian are the chief commercial varieties affected. These are important

varieties in the sections of western United States and southwestern Canada

where the production of sweet cherries is an important industry; thus in these

sections there is a correspondingly higher percentage of crinkle leaf in cherry

orchards. In Washington some growers have planted Napoleon (Royal Ann)

and Lambert in place of Bing and Black Tartarian, in order to avoid crinkle

leaf.

Suscept Range and Varietal Reaction

The list of aflfected varieties is based entirely upon the occurrence of

symptoms; since the disorder is apparently noninfectious, there is no way of

determining the absolute relationship of the symptoms on the various varieties.

Crinkle leaf has been reported on sweet cherry (Prunus avhim), and similar

symptoms have been seen by Reeves and Cochran ^^ on certain varieties of

domestica plum (P. domestica), notably the ItaUan Prune. Reeves (JM)

' Reeves, E. L., and Cochran, L. C. Unpublished data.

195
196 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

reported 1.1 to 1.3 percent of crinkle leaf on mazzard (P. avimn) seedlings.

Crinkle leaf is most common on the Black Tartarian and Bing varieties of

sweet cherry. It has been seen also on Black Republican, Eagle, Burbank, Dr.

Flynn, Ox Heart (of America), Shelton, and Waterloo Heart varieties.

Kinman (127) reported the occurrence of crinkle leaf on Lambert cherry,

but Reeves {1S4) stated that it has not been seen on Lambert or Royal Ann

(Napoleon). It is possible that crinkle leaf would have been as prevalent on

other symptom-expressing varieties as on Black Tartarian and Bing had they

been as widely planted.

Symptoms

Leaves on affected trees are variously misshapen and mottled (figs. 64 Ay

B, and 6), C) ; margins are often indented and abnormally serrated through

failure of blade tissue to develop. Some leaves are oddly and severely distorted

with deep sinuses and lobes and accentuated tips and bases. If removed from

the tree, they would not be recognized as cherry leaves. The inhibited areas are

usually lighter green and have a silvery upper surface and many more veins per

unit area than the remainder of the leaf, which is darker green than normal.

The light-green areas are present when the leaf first appears in the spring. Uneven expansion appears to be associated with a mixtiu'e of tissues some of which

have more chlorophyll than others. Leaves developed later in the growing

season, especially on sucker shoots, are often less affected than those produced

in the spring. The total leaf surface of a moderately affected tree is only

approximately three-fourths that of a normal tree; yet affected trees are not

noticeably reduced in growth.

The unfruitfulness of trees affected with crinkle leaf is not due to failure to

blossom, but many of the blossoms are smaller than normal and are visibly

defective. The peduncles are short, and most pistils are short and slender and

have a tendency to discolor early (ñg. 65, A). Some of the discolored pistils

are brown before the flowers open, and others become brown soon afterward;

and few develop into fruits. Such fruits are small, pointed, and often with a

raised suture (ñg. 65, C) ; they are attached with their long axis at an angle to

the stem. Flowers near the base of the preceding season's growth often fail to

open fully. The swollen buds on such growth become reddish, and some of

them remain in place for a number of weeks.

In many instances a tree may appear entirely normal, but upon close

examination small branches, twigs, or even a few leaves can be found to be

affected. It is common for trees to have both normal-appearing branches and

those affected with crinkle leaf. In some instances an entire tree is badly

afí^ected, and in others one or more branches may be severely affected and

others on the same tree bear normal leaves and fruits.

Transmission and Spread

Kinman (127), working with Black Tartarian cherry, showed that crinkle

leaf can be perpetuated through buds but is not transmitted either when

affected trees are top-worked with normal scions or when affected

scions are placed on normal trees. Zeller and Evans (259), working with

Bing cherry, reported transmission of a vein-clearing disease that is very

similar to crinkle leaf if not identical with it. Failing to repeat transmission

in later work, Zeller and Milbrath ^'^ concluded that the inoculated test trees

for which transmission was reported may have had an inherent form of crinkle

"2eller, S. M., and Milbrath, J. A. Unpublished data.
VIRUS DISEASES OF STONE FRUITS 197

leaf that was not apparent when the inoculations were made. This conclusion

is supported by the development of crinkle leaf in nursery trees propagated

from apparently normal trees that later were found to have a few spurs affected

with crinkle leaf. The orchard incidence of crinkle leaf, its occurrence in

figure 64.—Sweet cherry leaves affected -witli crinkle leaf: A, Bing; B, Black Tartarian. C, Comparable leaf from an unaffected Black Tartarian cherry tree.
198 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Figure 65.—A, Exposed pistils of blossom clusters from Black Tartarian cherry

affected with crinkle leaf; B, comparable pistils from an unaffected tree; C, fruits

and leaves from a Burbank cherry affected with crinkle leaf; D, comparable fruits

and leaves from an unaffected tree.

portions of trees developed from a single bud, and the common impression and

circumstantial evidence that crinkle leaf is spreading in individual trees as well

as in commercial orchards suggest to some investigators a transmissible agent.

Since growths from normal scions placed on trees affected with crinkle leaf

have remained normal for several years and thus without evidence of transmission, it is difficult to explain crinkle leaf on a virus hypothesis without a

new concept.

Careful observation is often required to detect traces of mild symptoms of

crinkle leaf, and these symptoms are often overlooked when a propagating wood

is selected. It is probable that the disease in many cases has been spread in

nursery stock propagated from such trees.

Hewitt and Philp found that some of the hybrid seedlings developed crinkle

leaf when the pollen parent was affected with crinkle leaf and the seed parent
VIRUS DISEASES OF STONE FRUITS 199

was normal. They noted crinkle leaf also on seedlings of which the seed parent

was affected and the pollen parent was normal. Reeves (184) reported the

occurrence of occasional crinkle-leaf-aifected seedlings among those grown

from certain commercial lots of mazzard seeds.

Control Measures

Control of crinkle leaf is a matter of avoidance and replacement. Crinkleleaf-aifected trees are common in the stock of many commercial nurseries.

This is undoubtedly due to lack of knowledge of the malady, insufficient care

in selecting budwood, or selection of budwood in the fall when crinkle leaf is

less easily detected than in spring and summer. Budwood sources should be

selected in the spring before the fruit is mature. No budwood should be

taken from a tree showing any crinkle-leaf-affected leaves. There is definite

need of a budwood-certification program and the prospect of success in control

is good if certified budwood is used. Affected trees may be top-worked with

good scions. It is doubtful whether it would be worth while to top-work old

trees, but top-worked trees up to 6 or 8 years old would fruit sooner than replants.

Remarks

Kinman (127) suggested that crinkle leaf is similar to the condition found

in variegated plants on which occasional normal leaves, twigs, and branches

occur. The rather common occurrence of variegated twigs on normal plants

might parallel the frequent occurrence of crinkle leaf twigs and branches on

otherwise normal cherry trees. When larger portions of a tree are crinkled, the

mutation might have occurred earlier in the life of the tree and might have been

perpetuated in succeeding growth. To support this hypothesis, it must be

assumed that a cherry variety like Black Tartarian or even some clones of

Black Tartarian are inherently constituted to mutate whereas others are not.

Willison suggested that some strains of Bing, Black Tartarian, and certain

other varieties possess genetic weaknesses to a greater degree than do other

strains and that in such strains sporting in the direction of crinkle leaf may

occur frequently. Spread of the disease could occur in this manner if such

strains were used in propagation even if they were apparently normal when

first set out in the orchard.

Milbrath and Zeller "^^ opposed the bud-sport concept as an explanation of

crinkle leaf. Their observations on crinkle leaf gave more support to the

disease concept. It is difficult, they claimed, to conceive of two or more

varieties such as Bing and Black Tartarian mutating such identical bud sports

or of a bud sport remaining latent for several years and then cropping out in

a single branch or in an entire tree. Crinkle leaf in the Bing variety especially

is difficult to explain on the hypothesis of mutation. The Bing variety is a

seedling of P. av'mm, and genetically all vegetative portions of it should be

identical. But in reality it is found that some subsequent propagations of this

one original tree develop a tendency to manifest crinkle leaf consistently, while

other lines of propagations from the same tree never produce crinkle leaf.

Kinman, observing crinkle-leaf-affected trees in California, found that the

number of crinkle leaf shoots are more numerous on old wood of trees that,

because of age, drought, or neglect, are low in vigor than on trees that produce good terminal-shoot growth. Trees somewhat low in vigor produce a

greater number of small lateral shoots along the part of the branch that is

^^Milbratk, J. A., and ZelJer, S. M. Unpublished data.
200 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

old than do vigorous trees, and it is among these shoots that the occurrence of

crinkle leaf is most frequent. The frequency Y\nth which lateral crinkle leaf

shoots develop on affected trees gives the impression that the trouble is

spreading as the tree grows older rather than making more frequent appearance on trees already añ'ected. Seldom is a new crinkle leaf terminal shoot

iound on a tree producing vigorous terminal shoots. But few lateral shoots

are produced by such trees along the part of the branch that is a few years old.
SWEET CHERRY DEEP SUTURE

By E. L. REEVES, EARLE C. BLODGETT, C. F. KINMAN, T. B. LOTT,

J. A. MiLBRATH, and S. M, ZELLER

Names of the Disease

The name ''deep suture" has become generally accepted by growers and

research workers although it applies only to the fruit symptom and makes no

reference to the accompanying leaf distortion. Other names which have been

applied are "long leaf" and "rough leaf." The name "rough leaf" was first

employed by Kinman in his early unpublished field records on the disease.

Causal Agent

Information concerning the cause of deep suture is incomplete. It has

been considered as possibly being a frequently occurring mutation. Deep

suture has not proved to be transmissible by the usual methods used to transmit virus diseases although the unusual malformation of both fruits and

foliage along with the sporadic orchard occurrence might possibly suggest the

presence of a transmissible entity.

History and Geographic Distribtxtion

Deep suture was first described by Reeves (1S3) as a disorder sometimes

confused with mottle leaf. Kinman observed the condition he referred to as

rough leaf in Sacramento Valley, Calif., cherry orchards during the late 1920's.

The condition has been reported on trees in California, Idaho, Montana,

Oregon, Utah, and Washington and in British Columbia, Canada, but since

its occurrence is common on some named varieties and mazzard seedlings, it

is suggested that deep suture is probably widespread.

Economic Importance

It is difficult to estimate the economic losses from deep suture because the

severity on affected trees varies and the degree of fruit malformation often

varies with the growing season. Deep suture has been reported as causing

moderate loss to Washington cherry growers, but it is not considered to be

so serious as crinkle leaf (184), Coe (66) grouped deep suture and crinkle

leaf together for purposes of the survey in Washington, and he stated that it

was not unusual to observe symptoms of both disorders on the same tree. He

reported that less than 10 percent of the properties inspected were found free

of the disorders.

In 1937 Kinman examined the Bing trees in three orchards in Sacramento

Valley and found that 13 percent of the trees observed were very severely

affected with deep suture and that more than 5 0 percent had a trace of the

condition.

In Oregon many of the Bing trees are affected, and it has been difficult to

find trees absolutely free of deep suture from which to obtain propagation

wood. In some districts fruit of affected trees is not picked because packers

will not accept it.

Crop loss from deep suture varies, because only parts of some trees are

affected and the portion of the fruits that are malformed even on affected

arms varies from season to season. Use of affected nursery stock results in a

201
202 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

multiple loss composed of the cost of the nursery tree plus the cost of

maintenance in the orchard until the tree is proved worthless.

Suscept Range

Since deep suture has not yet been proved infectious, the determination of

affected plants is based entirely upon visual symptoms. Deep suture has been

reported only on sweet cherry (Prunus avium). Reeves (ÍX3) stated that

the disorder was found in 193 8 on Bing and Lambert cherry trees, but it is

now questionable whether two affected trees supposedly Lambert were truly

that variety. Bing is the principal variety found affected, but occasional

Black Tartarian trees and mazzard (P. avium) seedlings exhibit symptoms.

One tree thought to be the Black Republican variety was observed affected,

and no doubt other varieties that exhibit symptoms may be found.

Symptoms

Bing cherry trees affected with deep suture have variable percentages of

malformed leaves (fig. 66) and fruits, and different trees display different

degrees of malformation. Sometimes entire trees are severely affected, but

at other times branches scattered through a tree or only certain lateral ones

Figure 66,—A, Leaves from a Bing cherry tree affected with deep suture; B, comparable unaffected leaf.
VIRUS DISEASES OF STONE FRUITS 203

exhibit symptoms. A severely affected tree viewed from a distance often has

a drooping appearance Hke one suffering from drought. Nursery trees affected with deep suture are often greatly dwarfed in height. When such

trees are transplanted, they grow very slowly and the foHage is sparse and

malformed.

Some trees show very Httle leaf malformation other than a thicker, more

leathery texture and a shght rugosity, while the leaves of others are reduced

to narrow ribbons, many of which may be only a midrib in parts and not over

1 inch wide in other parts. The mildly affected trees may show the characteristic deep suture type of leaves in the spring, but the leaves produced in

summer may be nearly normal in shape.

Some leaves are often actually longer than normal and their lateral veins are

shorter on one side or both sides of the midvein, whereas other leaves merely

appear to be longer because of their relative narrowness. The surface of the

leaf may be very rough, but not puckered. The periphery of some leaves

may be irregular, and perforations occur on a few. The leaf margins usually

have fewer serrations than normal, sometimes none in portions. A typical

leaf from a Bing cherry tree affected with deep suture is shown in plate 19,

bottom. A faint interveinal chlorosis may be present on some leaves during

the late spring, but it is less evident later in the season. Pronounced

chlorotic areas hke those found on trees affected with crinkle leaf do not

occur. Affected leaves often tend to develop a bright sheen on the surface

and are darker green than normal. Late-spring frosts sometimes cause

certain leaf malformations to develop on normal leaves; some of these may

easily be confused with the leaf symptoms of deep suture.

Affected fruits have a pronounced depression on the suture side and are

normally rounded at the end, as shown in plate 19, bottom. Fruits with pronounced deep suture are most often borne relatively near leaves that exhibit

symptoms.

Transmission

While fewer transmission experiments have been attempted with deep

suture than with crinkle leaf and over a shorter period, the two disorders

have behaved the same in all transmission tests thus far made. Zeller and

Milbrath, working in Oregon, and Reeves, working in Washington, made

numerous unsuccessful attempts to transmit deep suture. Growth from

normal scions grafted on trees affected with deep suture was normal, and

scions from affected trees grafted on normal trees produced affected growth

but failed to transmit the disorder to the stock.

Deep suture has been observed affecting mazzard seedhngs, although there

are no available data on the percentage of seedlings that might be so affected.

This could be interpreted as transmission of the disease through the seed, but

further evidence would be needed to substantiate such an interpretation.

Just as with crinkle leaf, there is considerable circumstantial evidence that

deep suture is spreading in commercial orchards; this spread suggests a transmissible agent. As far as reported, the possibilities of transmitting deep suture

have been inadequately explored.

Control Measures

Control is considered at present to be largely a matter of prevention, and

the careful selection of nonaffected propagation wood is especially recommended as a preventive measure. Scion wood should preferably be taken from

large bearing trees that have no trace of the disorder; and selection of bud-
204 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

wood from blocks where deep suture does not occur would be even more

desirable. It would be very desirable if nurserymen had access to established

''mother blocks" of trees free from the disorder and could take their propagation material from these. Budwood sources should be selected just before

fruit maturity.

Remarks

Zeiler and Milbrath made the following observations: Buds from the

normal portion of a Bing tree with only one isolated branch aft'ected with

deep suture near the top consistently produced both normal and deep suture

trees. Some showed deep suture foliage in the nursery row, and even though

they appeared normal in the nursery row others developed deep suture the

first year after transplanting and still others developed deep suture after 3

or 4 years. It is difficult to accept the hypothesis that this disorder has the

nature of a frequently occurring mutation, especially when a tree develops

normally for a while and later shows the disorder. The ability of deep suture

to remain latent points more to a virus behavior. Furthermore, it is difficult

to conceive why one Bing tree should remain normal, whereas another has

the ability to mutate freely and repeatedly to produce deep suture when the

Bing variety supposedly is the progeny of a single seedling of Priimis avium.

Since Reeves found that growth from normal scions grafted on trees affected with deep suture remained normal after 8 years and scions from afifected

trees grafted on normal trees did not transmit the disorder, it is difficult to

explain deep suture on a virus hypothesis without a new concept.
ALMOND BUD FAILURE

By E. E. WILSON and GILBERT L. STOUT

Other Common Names of the Disease

Shatter bud, crazy top, and mule tail.

Causal Agent

Unknown.

Geographic Distribution

Trees affected with almond bud failure occur in orchards scattered through

the interior valleys and coastal districts of north-central Cahfornia.

Economic Importance

Almond bud failure is of minor importance except in certain orchards in

which a high percentage of the trees of certain varieties develop the disorder

v/hile young. On such trees the yield is variously reduced, some trees producing only a few nuts.

Suscept Range

Nonpareil, Peerless, and Jordanolo varieties of almond (Pnmus amygdahis) are the only ones known to be affected.

Symptoms

The chief feature of the disease on all varieties is the failure of many of the

leaf and blossom buds to live and develop. On some twigs all buds grow, but

on others only a few buds do so. Twigs on which all buds fail retain life

during the spring, but eventually they die. Buds that grow produce shoots

rather than spurs. Such shoots appear normal the year they are produced, but

many of their buds fail to grow the following year.

Though the disorder commonly occurs on all branches of afifected trees,

sometimes it is confined to one or two branches. Occasionally all but one or

two branches of an afiiected tree show symptoms.

Elongation of affected limbs is more or less normal, but some twigs do not

attain normal diameter and in consequence are slender and willowy (ñg,

67, A).

When the terminal bud is among those dying, shoot growth is produced

from other buds. The shoots thus formed are often at various and peculiar

angles with the branches from which they arise. A succession of bud failures

results in a branch which is crooked (frequently growing back on itself,

especially in Peerless), sparse in foUage, and bearing deranged, slender, willowy

twigs more or less clustered at certain places (229, 251). In Peerless particularly, brown necrotic areas often develop on the bark of twigs produced

the previous season. These areas later become rough and cracked, forming

bands of rough bark up to a foot long on older wood.

In all varieties leaves and blossoms on affected branches, though fewer than

on nonaffected branches, are normal in size, shape, and color. A delay in the

opening of blossoms, however, is common on severely affected trees.

Transmission

Up to the present time the disorder of the Nonpareil and Peerless varieties

has not been transmitted to either of these varieties, though it has been budperpetuated from both. Nonaffected Nonpareil and Peerless trees grafted

205
206 HANDBOOK 10, ü. S. DEPARTMENT OF AGRICULTURE

Figure 67.—A, Nonpareil almond affected with almond bud failure, showing in center

one vigorously growing branch less affected than the others; B, Nonpareil almond

tree showing at right unaffected branches that developed from a healthy graft

placed on understock 7 years previously and at the left the branches that developed

from the affected understock.
VIRUS DISEASES OF STONE FRUITS 207

with scions from affected Nonpareil and Peerless trees have remained without

symptoms of bud failure for 6 years, though about 80 percent of the branches

produced from the affected scions developed symptoms within 3 years.

Moreover, nonaifected Nonpareil scions grafted onto affected Nonpareil trees

have remained symptomless for 11 years.

In figure 67, B, is shown such an almond tree grafted 7 years previously.

In another series growth from buds taken from affected trees and placed on

seedling peach and bitter almond developed bud failure symptoms within 3

years.

Inasmuch as the disorder was found in the Jordanolo variety only recently,

transmission tests with this variety are not yet complete.

In general, the symptoms of the disorder on Nonpareil, Peerless, and

Jordanolo almonds resemble those of the transmissible bud failure of Drake

almond described on page 191. The failure of buds to grow is a basic and

characteristic symptom of both diseases. The symptoms of almond bud

failure on naturally affected Nonpareil almond are similar to those produced

on this variety as a result of inoculation with scions from Drake trees affected

with Drake almond bud failure. The symptoms of almond bud failure on

Nonpareil, Peerless, and Jordanolo varieties differ from those on the Drake

variety affected with Drake almond bud failure as follows. (1) Affected

twigs are slender and willowy instead of normal in diameter, and they arise at

various and peculiar angles instead of normal ones. (2) Leaves are normal in

size, color, and shape and are shed at the normal time instead of being larger

and slightly darker green than normal and persisting late in the fall, sometimes

even until spring. (3) The fruits are normal in shape instead of being somewhat malformed.

Judging from the result of transmission studies the malady of Drake almond

may not be the same as that of the other three varieties. Differences in certain

details of symptoms would seem to confirm this view. Inasmuch as not all

possible methods of transmission have yet been exhausted, the authors regard

the placing of the Nonpareil, Peerless, and Jordanolo disorder in a nontransmissible classification as provisional only.
NONINFECTIOUS PLUM SHOT HOLE

By C. O. SMITH and L. C. COCHRAN

Name of the Disease

The name ''shot hole" has been variously apphed to both infectious and

noninfectious plant diseases. The disease described in this section is of the

latter type, is genetic as evidenced by perpetuation in buds, and is heritable

as evidenced by passage through seeds.

Geographic Distribution

The disease has been seen rarely in native thickets on seedlings of wildgoose, or pottawattamie, plum (Primus munsoniana) in southwestern United

States. Many selections have been made from seedlings of ?. iminsoniana

and are widely grown as dooryard trees and in small plantings in southern

United States. The most common of these have bright-red fruits and are

called wildgoose. Shot hole of various types has been seen on individual trees

scattered through the area.

Economic Importance

Noninfectious plum shot hole is not of commercial importance, but it may

cause confusion when it is associated with infectious diseases.

Suscept Range

Noninfectious plum shot hole (205) was originally described on Beaty

plum, which, according to Wight {245), is a hybrid between P. angmtifolia

varians and P. iniinsoniana. Individual plum seedlings from seed collected

from open-pollinated pottawattamie plum collected in Utah were variously

affected, symptoms ranging from purple spots to large necrotic spots and

shot holes indicating genetic segregation. It seems logical that the trouble may

be the result of a genetic weakness of P. munsoniana and that it should be

expected in plums arising as seedlings and hybrids of this species.

Symptoms

Early-spring growth of affected trees appears normal. As the season

progresses, the older leaves at the base of the shoots develop translucent

flecks, which rapidly enlarge. The centers of these spots turn brown {iig.

6%, A), and in the majority of cases the brown areas separate from the rest

of the leaf at a definite line of cleavage and drop out. The resultant shothole condition develops progressively toward the apex of the shoots, and by

midsummer, when growth has become slower, the foliage appears riddled with

holes {i^g. 68, By C). The spots and holes on leaves of most trees range from

pin-point size to J^- to ^-inch diameter, the size usually being inversely

proportional to the number on the affected leaf. Individual affected seedlings

vary greatly in symptom expression, some being severely and others only

mildly affected. On some the spots are all small and appear as purple dots,

or freckles, and the centers do not fall out. On others the spots are all large,

and the centers drop out as they are formed. The spots are usually circular,

but the larger spots may be irregular in shape, especially where t^wo or more

spots run together or occur in the angles of veins.

Transmission

When buds or scions taken from diseased plants are placed on unaffected

sister seedlings or on any of several horticultural plum varieties and on other

208
VIRUS DISEASES OF STONE FRUITS 209

Figure 68.—Beaty plum seedling affected with noninfectious plum shot hole: A, Early

stage, sho"wing zones around dark centers; B and C, advanced stages.

species of Prunus the shot-hole symptoms develop on the leaves of shoots

arising from the affected bud, but in no case have they been seen on the understock below the point of grafting. It can be argued that failure of transmission is due to nonsusceptibllity, but until there is some evidence of transmission it seems most logical to assume that this disease belongs to the budperpetuated, nontransmissible group.

Remarks

Noninfectious plum shot hole described here appears to be connected with

P. munsoniana. The trouble occurs on certain other plums of the wildgoose

type, most of which have been selected from P. munsoniana, and should be

expected when this plum is used as a parent. No connection has been established with Italian Prune leaf spot as described by Blodgett {16), but the two

diseases have characters in common and may be similar.
ITALIAN PRUNE LEAF SPOT

By EARLE C. BLODGETT and B. L- RICHARDS

Other Common Names of the Disease

Italian Prune leaf spot is sometimes called shot hole.

Geographic Distribution

Leaf spot is generally found wherever the Itahan Prune variety is grown

in Idaho, particularly in the southwestern part. It occurs in the MiltonFreewater and The Dalles districts of Oregon; in Yakima Valley, at Walla

Walla, and in Wenatchee Valley, Wash., and wherever the Itahan Prune is

grown in Utah. Leaf spot apparently occurs in the Midwest, because afifected

nursery stock has been received from an Iowa nursery, and possibly it occurs

farther east. It is, of course, possible that the Iowa nursery stock was

propagated in the West or that scion wood from western sources was sent east.

What appears to be a disease belonging to the same class was described by

Smith and Cochran (205) on Beaty plum in California.

Economic Importance

The actual loss from Italian Prune leaf spot is impossible to estimate accurately, but the disease is regarded as the cause of serious losses in quantity

and quahty of Italian Prune fruit. Losses vary with season, indicating an

effect of environmental factors during the growing period. It appears from

surveys in Idaho that in general the percentage of affected trees is greater in

young orchards than in old plantings. Richards observed in Utah that the

older orchards seem to be more severely affected and that Italian Prune production is on the way out, principally because of leaf spot.

Suscept Range

The Italian Prune variety (Prunus domestica) is the only host considered

here, although Smith and Cochran (205) described a similar type of disorder

on Beaty plum in CaHfornia. Blodgett observed perpetuation of normal

leaves on growth from scions of an unidentified prune of the Itahan Prune

type grafted on severely affected Itahan Prune stock.

Symptoms

The symptoms of Itahan Prune leaf spot apparently do not appear until

early summer, as the first growth seems to be normal. The spots on the leaves

vary in size from very small ( 1 to 2 mm.) to large, round or irregular blotches

of dead tissue (pi. 18, B). Sometimes the leaf margins die and dry up. The

affected tissue is brown and has definite margins, and there are often distinct

concentric zones in the spots. Frequently the spots drop out, leaving a shothole condition. A leaf mottle frequently precedes or accompanies the necrotic

spotting (22). This condition is widely prevalent and is characterized by

light-green or rusty areas in the leaves. The motthng may be very indistinct

or very striking, much like mosaic symptoms. Motthng may be closely associated with leaf spot, or it may occur largely as the only symptom on certain

trees.^ It may be a phase of leaf spot or a separate disorder. Early and severe

defoliation may result in a heavy fruit drop or in a yield of poor-quahty or

sunburned fruit.

210
VIRUS DISEASES OF STONE FRUITS 211

Trees grown from stock which showed symptoms in the nursery may be

dwarfed, and usually they are not satisfactory, since terminal growth is

decidedly short. On less severely affected trees growth may be nearly normal.

No particular effect on bloom or fruit set is noted except in the most severe

cases. On some affected trees there is distinct evidence that varying amounts

of chlorosis accompany leaf spot. When this occurs, tree vigor is further

reduced and usually a tendency toward a rosette condition is apparent. Recent

observations indicate that expression of ItaUan Prune leaf spot is less severe on

trees on myrobalan rootstock than on those on peach rootstock.

Diagnostic or Unusual Characteristics

Perhaps the most striking characteristic of Italian Prune leaf spot is the

severe form, which is erratic in occurrence. Some trees are affected so

severely that they are dwarfed and their yield is greatly reduced. Other trees

are less severely affected, but the yield and the quahty of the fruit are impaired

even when tree growth is only slightly affected. The severity of effect on

individual trees varies widely from year to year.

Transmission

The disorder has not been transmitted, but it can be easily bud-perpetuated

(16).

Control Measures

Propagating wood should be taken from healthy stock only. Removal of

affected trees is recommended only when the orchard is young or after the

trees develop severe symptoms and it has been shown that contributing factors

cannot be controlled.

Remarks

Leaf spot is regarded as probably a genetic abnormaHty even though it is

influenced greatly by soil and weather conditions. Many observations indicate

that the disease may be more severe on trees near barnyards, chicken runs,

or driveways and during very hot, dry seasons. It is believed that a rather

complex situation exists in regard to this leaf spot and that a great deal more

work is necessary to answer pertinent questions. Recent observations indicate

that expression of ItaHan Prune leaf spot is less severe on trees on myrobalan

rootstock than on those on peach rootstock.
ITALIAN PRUNE SPARSE LEAF

By E.\RLE C. BLODGETT

Name of the Disease

"Sparse leaf" is the only name ixsed. The condition might appropriately

have been called sparse fruit or unfruitfulness because a&cted trees bear

sparsely.

Geographic Distribution

Several affected trees have been found in one orchard in southv/estern Idaho.

These are old trees, which, according to the grower, have shown symptoms

since the orchard was started. They have been under observation since 1942

(27).

Economic Importance

Losses from sparse leaf are minor.

Suscept Range

The disorder has been observed only on Italian Prune (Pmmis domestica).

Symptoms

Trees affected with sparse leaf are large and round-headed and tend to be

open in type of growth. When the trees are young, growth is probably nearly

normal in amount. In the orchard, affected trees can be identified easily in

the leaf stage by their lack of fohage and in the dormant stage by their

shape. There may be an abnormal delay of about 10 days in time of blooming

{27) and of leafing out {22; 25, pp. 403-404).

Affected trees bear very sparingly. The prunes are perhaps larger than

normal, but they seem to be normal in color, shape, and texture.

The foliage on aft'ected trees is extremely sparse in comparison with that

on normal trees. The sparseness seems to be due principally to the lack of

small-twig growth on which leaf and fruit buds are normally borne. Apparently the lower and inner small branches either do not form or die soon after

they are formed. It is estimated that the leaf surface of affected trees is

Kttle more than 50 percent of that on normal trees. The foHage is confined

largely to twig terminals on the periphery of the tree. The early leaves in

particular are deformed, looking somewhat similar to sweet cherry leaves

affected with crinkle leaf. They are smaller than normal and have irregular

margins and diffuse mottling.

Diagnostic or Unusual Characteristics

The open center of mature trees, the late blooming and foHation, and the

sparseness of foliage are characteristic.

Transmission

Tests started in Idaho gave evidence of bud perpetuation, but the experimental trees were lost before it was possible to determine whether the disorder was transmissible. There is no good evidence of orchard spread.

Control Measures

Because affected trees bear sparingly, they should be replaced with good

nursery stock, Budwood should be obtained from healthy trees.

Remarks

Sparse leaf is regarded at present as probably a genetic abnormaHty.

212
PEACH VARIEGATION

By EARLE C. BLODGETT

Other Common Names of the Disease

In the earliest report peach variegation was called calico (Í5), but after

transmission attempts failed it was regarded as a chimera (24).

Geographic Distribution

Variegation has been observed on one J. H. Hale peach tree (original) near

Caldwell, Idaho, and what appear to be the same symptoms have been seen

on one Elberta tree at Emmett, Idaho. Similar variegations were observed by

Reeves *® on a J. H. Hale peach growing in the Crescent Bar district near

Trinidad, Wash.

Economic Importance

Variegation is regarded as of very minor importance, and interest in it is

due principally to its similarity to peach virus diseases.

Suscept Range

Variegation has been observed on J. H. Hale peach {Prunus pérsica)

(original), and what appeared to be the same disorder has been seen on Elberta

peach.

Systnptoms

On leaves affected with variegation (fig. 69) there are rather sharply

' Reeves, E. L. Unpublished data.

Figure 69.—Leaves of J. H. Hale peach affected with variegation.

213
214 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

delimited areas with at least three distinct shades of green. Some portions

of the leaves are cream-colored to white. Often sectors or angular portions

of the leaves are affected. Growth of twigs on the affected parts of a tree

is materially reduced^ and yellow coloration of bark tissue is sometimes

associated with the condition.

Diagnostic or Unusual Characteristics

The presence of sharply defined areas of three shades of green in the

affected leaf tissue is characteristic. Variegation should be distinguished from

peach calico, a virus disease, in which leaf tissue is either green or white with

a gradient between the two.

Transmission

Variegation is not transmissible, but it is bud-perpetuated. Three Slappey

peach trees and five peach seedlings were budded with buds from trees affected

with variegation, but no transmission resulted. In amount and pattern the

variegation in the growth from inserted buds corresponds to the variegation in

the leaves which subtend such buds.

Control Measures

Although variegation is not important at present, it is suggested that care

be taken to use only wood from healthy trees for propagation.

Remarks

The exact nature of variegation is not known. It has been suggested that

it is a chimera or genetic abnormality (24), The occurrence is apparently

rare.
DEFICIENCY AND EXCESS TROUBLES THAT

RESEMBLE VIRUS DISEASES

SIMILARITY OF SOME NUTRITIONAL DISORDERS AND

VIRUS DISEASES

By F. P. CULL INAN

Trees of the various species of Prunus when grown in soils deficient in one

or more of the essential mineral nutrients develop symptoms frequently mistaken for those caused by viruses. Various deficiency and excess disorders

of stone fruits are described and recognizable differences between them and

certain confusing virus diseases are pointed out in order to help nurserymen

and others working with stone fruits to make correct diagnoses of disorders

found in the field.

If plants of Pmnus species are grown in sand or water cultures from which

essential elements are withheld, normal metabolism is affected and abnormal

leaf and twig growth result (322). Some of the deficiency symptoms are

specific and serve as a basis for diagnosis of Uke symptoms on trees grown

under field conditions. In some cases the leaf pattern, for example, may be

characteristic of a particular element deficiency, but in other cases it alone

is not diagnostic. Thus, when iron, magnesium, manganese, or potassium is

deficient varying degrees of reduction of leaf chlorophyll are apparent (ñg.

70). Additional symptoms are needed along with the particular type of

chlorosis to differentiate these deficiencies. Virus diseases are also responsible

for varying degrees of leaf chlorosis. The pattern of the chlorosis or the

markings produced in the leaf are diagnostic of some viruses that produce

characteristic so-called ring spots. The basic cause of chlorosis may be nutritional, whether chlorosis is due to the lack of a mineral element or to the

presence of a virus or a virus complex, because both disturb the normal

metabolism of the plant. Similarly, other symptoms of mineral deficiencies

and virus diseases may be due to functional disturbances.

Peach trees affected with the virus disease called phony have leaves that are

darker green than normal for a variety. The leaf blade of phony-affected

Elberta is more flattened than normal, and it is not wavy or fluted like the

lamina of a normal leaf. Similar symptoms are observed on peach trees grown

in a medium deficient in phosphorus. It has been shown, however, by

chemical analysis that peach leaves from phony trees are not deficient in

phosphorus.

A marked symptom of zinc deficiency in the soil is the rosette and littleleaf condition. This symptom is diagnostic of zinc deficiency on all stone

fruits. Lack of other essential elements in the soil does not produce similar

growth effects. Trees affected with the virus disease called "peach rosette," as

the name implies, also have little leaves in rosettes (pi. 2, A). Other symptoms

of zinc deficiency help to distinguish it from peach rosette.

"Dieback" is a general term referring to death of the growing points or

the ends of upright branches. Sometimes the affected part may be 2 or 3 feet

215
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ligure 70.—Elberta peach leaves showing symptoms of mineral deficiency when trees were grown in sand cultures with indicated

element withheld: A, Phosphorus; B, manganese; C, nitrogen; D, iron; E, magnesium; F, calcium; G, potassium. H, Comparable

leaf from tree grown on a complete nutrient.
VIRUS DISEASES OF STONE FRUITS 217

long. Dieback may be caused by mineral deficiencies or by virus and fungus

diseases. In cases of severe zinc deficiency the little-leaf or rosette condition

may be observed when the leaves first open and shedding of leaves and dieback

(see ñg. 76) may occur later in the same season or in the following one.

Thus, another symptom characteristic of zinc deficiency is dieback. Similarly,

when boron, calcium, or copper is deficient, death of the growing point may

result. New growing points arise back of the injured area and clusters, or

rosettes, of shoots result. These in turn may die back. In California prune

trees grown in potassium-deficient soil frequently show dieback.

One of the characteristics of leaves on trees suffering from potassium

deficiency is puckering or crinkling of the tissue of the blades near the midrib

due to the unequal growth of cells (see iig. 71, B). Leaves of trees affected

with the peach mottle (pi. 12, D) show a similar characteristic. Another

symptom of nutritional disturbance noted particularly on the leaves of peach

trees showing potassium deficiency is the tendency of the leaves to curl upward and roll in from the edge (see ñg, 72, B). Rolling is observed also on

trees affected with such virus diseases as western X-disease, little peach, and

peach yellows. It is therefore apparent that rolling of the leaf alone is not

a diagnostic character. Leaves of peach trees that have their root systems

disturbed by mechanical injuries, a high water table, root or stem borers, or

other causes have a tendency to roll. In diagnosing troubles suspected of being

due to a nutrient deficiency, it is therefore necessary first to eliminate the possibility of factors other than nutritional ones as contributing causes. When

this is done, such symptoms, for example, as leaf rolling, chlorosis, marginal

scorch, crinkling, and spotting that are characteristic of potassium deficiency,

become reliably indicative of the cause of the disorder.

Stone fruits, particularly peach, plum, and cherry, show shot holes in the

leaves as a result of injury. This condition may be brought about by a

mineral deficiency, a virus, a fungus, a bacterial infection, or a toxic chemical,

but it is characteristic of some varieties. In general, when leaves of stone

fruits show localized spotting from any cause, the injured or necrotic tissues

drop out, leaving holes. This has been mentioned by some observers in the

case of severe nitrogen and potassium deficiencies. Similarly, leaf spot fungi

or bacteria may cause spots. Furthermore, materials present in toxic amounts,

either in the soil or on the leaf as a result of spraying, may cause definite

injury and produce shot holes. Accumulation of arsenic in the soil in toxic

amounts, for example, causes typical shot hole and other leaf symptoms and

marked defoliation, but the fruits hang on the tree (see pi. 27, E, F.), Soluble

arsenic on the leaf resulting from the use of insecticides in spraying may

result in the same kind of leaf symptoms and in defoliation if the injury is

severe. In the case of the western X-disease shot hole is also one of the

symptoms and marked defoliation may occur. With this virus disease, however, fruits also drop; this effect is in contrast with that of arsenic toxicity.

Late in the season a few varieties of peach may develop in the leaves shot

holes that apparently are not caused by nutritional or disease disturbance.

An example is the Iron Mountain variety. Under some conditions this variety

develops light-gray leaf spots which fall out, giving a leaf condition similar

to that on trees affected with western X-disease. The leaves, however, do not

fall prematurely.

In the Western States, where both zinc-deficiency disorder and western

X-disease occur on stone fruits, it is sometimes difficult to determine the
218 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

cause of the symptoms noted, especially when both troubles may be present

on the same tree. Thorne and Wann (315^ 315a) from observations made in

Utah pointed out the following differences and similarities:

1. Western X-disease docs not cause reduction in leaf size; zinc deficiency causes little leaf.

2. Western X-disease causes the leaves to curve downward and to roll in from the edges;

zinc-deficiency leaves do not curve downward, but have wavy, crinkly edges.

3. With western X-disease the leaves may drop off in midseason, resulting in completely

bare twigs; in severe cases of zinc deficiency, defoliation may occur but a rosette of small

leaves is retained at the tip of the twig.

4. The chlorotic and red markings caused by w^estern X-disease tend to be parallel with

the leaf margin and extend across the lateral veins; in zinc deficiency the leaf markings are

in general at right angles to the margin and in the areas between the lateral veins.

Thorne and Wann concluded that when all these general characteristics are

taken into consideration a correct diagnosis of the disease is usually possible.

Pruning, fertilizing, and otherwise providing good cultural conditions for

affected trees may correct the trouble if it is the result of a nutrient deficiency.

On the other hand, symptoms of virus diseases may be accentuated by these

treatments. Thus, an}^ method of stimulating growth is a way of determining

whether the disorder is nutritional or virus in nature. Leaf sprays may be

very effective in indicating quickly the cause of some disorders, particularly

those resulting from the lack of such elements as iron, manganese, copper, or

zinc. Definite proof of the virus nature of a disorder may be obtained by

transmission studies. When buds are taken from affected trees and inserted

into healthy ones and the latter develop typical disease symptoms, this is

conclusive proof that the disorder is infectious.

Analyses to determine the nutrient content of leaves of trees showing

deficiency symptoms are helpful in diagnosis. In fact, where symptoms are

not suflSciently distinct for visual diagnosis, leaf analyses may prove to be

the most dependable criterion. More data have been obtained on deficiency

disorders of peach than of other stone fruits. A mild case of potassium

deficiency of peach trees growing on a sandy loam where the only symptoms

were light-green leaves of small size may be used as an example. The potassium content of the leaves was found to be 1.2 5 percent on a dry-weight

basis early in the season. When potash was added to the soil and the leaves

were sampled late in the growing season, the potassium content had increased

to 2.5 percent. The leaves were then bright green and the new ones were

normal in size. Peach leaves with marked symptoms of potassium deficiency

usually show a potassium content of about 1 percent or usually below on a dryweight basis (284), Similarly, with other nutrient deficiencies, such as

nitrogen, phosphorus, and manganese, leaf analyses are a valuable aid in

diagnosis.

Excess salts in the soil may cause nutrient disturbances that result in leaf

symptoms somewhat similar to those caused by nutrient deficiencies or by

virus infections. Injury to stone fruits has been observed in California and

other Western States in orchards irrigated with saline water. Fluctuations in

the water table may be responsible for a movement of salts accumulated at

lower levels in the soil to the root-zone area of a tree. Leaf scorch of stone

fruits caused by injury from excess sodium (see pi. 27, G, D) is an example

of the kind of disorder produced.

It is apparent that it may not always be easy to make a prompt, correct

visual diagnosis of fruit-tree disorders in the field. In some instances the

symptoms of a particular deficiency or a virus disease may be clear-cut and
VIRUS DISEASES OF STONE FRUITS 219

easily recognizable. In other cases, where the disorders are mild and the

symptoms are confusing, it may be necessary to study the cause.

There are various methods available for determining the nutrient status

of trees. Considerable data have been accumulated to show the value of using

the leaf as an index of nutrient availabiUty. Soil analyses may not be rehable

since they may show an ample supply of some elements in the soil solution, but

for various reasons these nutrient elements may not be available to the plant.

In some cases a quaHtative analysis may be sufficient to indicate the probable

deficiency. There are various well-known quick-test methods that may be

employed to confirm suspected deficiencies (285). A quantitative method,

however, is usually more dependable. Chemical, colorimetric, spectrophotometric, and spectrographic analyses have been worked out for all the essential

mineral elements.

The detailed descriptions of the nutrient disorders (pp. 222 to 251) and of

virus and virushke diseases (pp. 1 to 214) give more complete information

that should help in the identification of abnormal growth conditions. The

key (p. 220), which points out differences in the nature of nutrient disorders

and their appearance on young and older leaves, should be helpful in differentiating disorders with one or more symptoms in common on peach. A

valuable key has been pubHshed by Wallace (319) as a guide to the diagnosis

of mineral deficiencies in various plants.

Some nutrient deficiencies now occur in stone-fruit-producing districts

where they were not observed in the past. Certain growth abnormalities are

noted in some orchards and not in others growing relatively close by on the

same soil. It is possible that additional districts may be involved in the future.

Soil-management, fertiHzer, and irrigation practices, together with heavy

production, may result in the occurrence of deficiency disorders, particularly

on soils poorly supplied with essential elements.
KEY TO NUTRIENT DEFICIENCIES IN PEACH TREES

By O. W, DAVIDSON

I. Symptoms in the early stages of the deficiency general on the

whole tree or tending to be localized on the older leaves of

current-season growth,

A. Symptoms rather generally distributed, but most prominent

on lower leaves of current-season growth; without areas of

dead tissue on leaves except when deficiency is advanced

and severe.

1. Leaves yellowish green; discoloration beginning on eld,

mature leaves and progressing toward tip. Reddish and

purplish-red discolored leaf spots. After prolonged deficiency, twigs hard and slender and leaves small Nitrogen

2. Young and nearly mature leaves dark green; mature leaves

tan or ocher to dark green. Old leaves usually mottled,

with light-green areas between dark-green veins. Progressive defoliation of mottled leaves from bases toward tips of

twigs. Abnormal amounts of purplish pigment in stems

and leaf petioles, especially during cool summer weather.

New twigs slender and leaves small and strap-shaped if

deficiency continues Phosphorus

B. Symptoms appearing first on mature or lower portion of

current-season growth and occurring as mottling or

chlorosis; with or without spots, blotches, marginal scorching, or other dead areas on leaves.

1. Dead areas on leaves, varying in size from very small spots

or dots to patches or extensive marginal scorching. Leaves

usually crinkled and somewhat curled. Dead areas developing first on mature leaves near middle or lower half

of current-season growth. Twigs usually slender. Fruit

buds sparse on twigs Potassium

2. Dead areas occurring as fawn-colored (or dull-brown if

exposed to rain or dews) patches on most mature, large

leaves. Progressive dropping of affected leaves toward the

tips of current-season twigs. Defoliation severe, leaving

tufts or rosettes of thin dark-green leaves at the terminals. Magnesium

3. Leaves at tips of new growth small, narrow, more or less

crinkled, and chlorotic; twigs slender, with very short

internodes at tips and therefore rosettes of leaves. Progressive defoliation from bases to tips of twigs Zinc

IL Symptoms appearing first on young tissues and tending to be

localized at the terminals of twigs, which die back from

terminals; severe necrosis on newly developed or nearly

mature leaves.

220
VIRUS DISEASES OF STONE FRUITS 221

A. Immature leaves, especially the first one or two on very

young tvàgs, and those at terminals injured, particularly

along the margins. Dark-brown dead areas along midribs of nearly mature leaves. Following severe injury to

foliage at terminals, twigs dying back for an indefinite distance. New branches usually developing a short distance

below injured tips. Symptoms always associated with extensive injury to roots

B. Leaves more or less chlorotic and wrinkled or otherwise

deformed and sometimes abnormally thick and brittle,

particularly at tips of twigs. In severe cases, dieback

of twigs. Fruits sometimes showing necrotic areas and

cracking excessively even in dry seasons Boron

C. Young leaves chlorotic, but veins usually green. In severe

cases, young leaves, including veins, sometimes creamcolored and with dead areas usually at tips Iron

Calcium
NITROGEN DEFICIENCY

By E. L. PROEBSTING and O. W. DAVIDSON

Geographic Distribution and Economic Importance

Lack of an adequate supply of available nitrogen is by far the most common and most important cause of deficiency disorders in stone fruits. This

deficiency occurs in every major fruit district in the country unless nitrogen

is applied. Nitrogen is the nutrient element to v^hich peach trees show the

greatest response in growth (283). Conversely, when nitrogen is lacking,

growth and production of fruit are greatly reduced. Stone fruits are usually

grown on light soils and on sites with good air drainage, where the springfrost hazard to blossoms is reduced. Peaches, however, are grown on a

wide range of soils varying from sand to gravelly loam, shale, and clay. Trees

on all of these soils may respond to nitrogen.

The losses sustained from lack of nitrogen are not great as measured in

tree mortality. Trees survive for many seasons even though they may show

severe nitrogen-deficiency symptoms. The losses from an economic standpoint in terms of growth and yield are significant, and profitable commercial

production is obtained only when nitrogen is adequate (272^ 307).

Stone-Fruit Species Affected

On a given soil in California peach (Pruitus pérsica) frequently shows

symptoms first, but almond (P. aimygdahis) and Japanese plum (P. salicina)

show them a little later. Domestica plum, or prune (P. domestica)^ may not

show any marked symptoms except reduced growth {3 07, 3 08),

In eastern United States also peach shows the most marked symptoms of

deficiency when nitrogen is lacking, but here as well as elsewhere symptoms

are also shown on all other species of stone fruits where the element is not

available in sufficient amounts.

Symptoms

The pale-green to yellow color of the leaves of all plants grown in a soil

low in available nitrogen is a well-recognized symptom of nitrogen deficiency

(272) (pi. 23, A). When the supply of nitrogen in the soil is limited, trees

gradually redistribute a large portion of their nitrogen from old to new tissues.

As a result, the mature and nearly mature leaves turn from dark green to

yellowish green. The yellow color of these leaves gradually increases, and

the petioles and veins become tinged with red. By this time, linear growth

of twigs has been checked and the leaf size is reduced. Moreover, the twigs

and leaves are relatively hard. In 1 to 3 weeks red or red-brown spots appear

between the large veins of the leaf blades if the deficiency is acute. In

advanced stages of nitrogen deficiency, many of the reddish spots develop

into necrotic areas. Gradual abscission of the leaves from the base of the

current-season growth toward the tip follows.

Stone fruits growing in sod usually show lack of nitrogen more quickly

and severely than trees under cultivation. The small, pale-green leaves of

unfertilized trees growing in sod, the early cessation of growth, and early leaf

fall are characteristic symptoms of nitrogen shortage. The terminal-shoot

growth is frequently short and thickened, and the fruit buds are numerous. The

222
VIRUS DISEASES OF STONE FRUITS 223

percentage of flowers setting fruit is greatly reduced. In case of severe

nitrogen shortage the shoots also are short and of slender diameter, and the

number of fruit buds is less than on normal trees. Potassium-deficient trees

also frequently have small, light-green leaves similar to those on nitrogendeficient trees. In the case of potassium deficiency, however, the terminal

shoots are more slender and the internodes are long. The red spotting of

leaves of severely affected trees is characteristic of deficiency of nitrogen.

Lack of this essential element in the soil is the only áeñciency resulting in

reddish discoloration of the leaf.

Control Measures

Nitrogen deficiency is easily corrected by the application of inorganic

sources of nitrogen such as ammonium sulfate, sodium nitrate, or ammonium

nitrate or of organic material containing soluble nitrogen (285j 307) (pi. 23,

AC).
POTASSIUM DEFICIENCY

By DAMON BOYNTON, O. W. DAVIDSON, and OMUND LILLELAND

Geographic Distribution and. Economic Importance

Potassium-deficiency symptoms have been observed on various stone fruits

in ail counties in the fruit belt of western New York (27), 277). Potassium

deficiency is a commercial problem in only a small part of the stone-fruit

orchards, where it may retard development of trees, reduce productivity, and

make fruits inferior in size and quality. The disorder has been reported on

peach also in South Carolina (3 09, 510)y Maryland (284), Pennsylvania

(287) y and New Jersey (285). In fact, it appears to have been found in

many orchards in the Coastal Plain and Piedmont regions extending along the

Atlantic seaboard from the Carolinas to New York and the Niagara Peninsula

of Canada. Symptoms of potassium deficiency have also been noted in peach

orchards on light sand in Michigan and on peach in Indiana and sour cherry

in Wisconsin. Disorders caused by potassium deficiency are found in more

peach-producing districts than those caused by other essential elements except

nitrogen, While the number of trees affected in some orchards may vary

from a few to many, the acreage involved in the peach sections of eastern

United States is relatively small. In California disorders due to potassium

deficiency have been limited to prunes in the foothill districts west of Morgan

Hill and Gilroy and to a few localities near Chico (296, 299).

Stone-Fruit Species Affected

Peach (Prnntcs pérsica), sour cherry (P. cerasus), and domestica plum (P.

domestica) are all affected with potassium deficiency.

Symptoms

Leaves of potassium-deficient trees usually look normal in spring and

early summer except for being lighter green and having somewhat the appearance of leaves low in nitrogen. Symptoms are more prevalent and severe

in dry summers than in wet ones. They are more severe on heavily loaded

trees. They occur on trees growing on various kinds of soil, whether or

not the subsoil is well drained. Although young trees are more commonly

affected than mature ones, symptoms have been noted on bearing trees of

plum, peach, and sour cherry.

Peach.—The initial symptom of insufficient potassium on peach trees is

a slight yellowing of the leaves. Inasmuch as this symptom is similar to that

of a lack of nitrogen (pL 23, A, B), it is not diagnostic. The older leaves

on affected trees are lighter green than those on unaffected trees, and under

good cultural conditions they may start to fold or roll toward the tipper surface (pi. 23, B). Some interveinal chlorosis may be apparent, and there may

be pronounced wrinkling at the midrib {ñg. 71, B). As the season progresses,

the margins of the folded leaves fade in color and turn brown (pi. 24, B),

Later, small straw-colored necrotic spots and blotches develop within the blades

(ûg. 70, G) and straw-colored necrotic stripes appear along the margins of

leaves on the midportion of the current-season growth (pi. 24, C). After

exposure to dews and rain the necrotic tissue becomes dull brown. The necrosis

due to potassium deficiency has been commonly called leaf scorch. If the

224
VIRUS DISEASES OF STONE FRUITS 225

deficiency continues, necrotic areas develop on leaves progressively toward both

the tips and bases of the stems. New growth continues to develop slowly at

the tips, and considerable rolling is noticeable. The twigs are usually very

figure 71.—Terminal shoots from Elberta peach trees in orchard at Beltsville, Md.:

A, Adequately supplied with nitrogen and potassium; B, adequately supplied with

nitrogen. Crinkling of the older leaves is evident in B,

«91793°—51—18
226 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

slender (fig. 72, B; pi. 24, A), and fruit buds are sparse or lacking. On

severely affected trees the leaves are apt to be small (pi. 24, B) and the terminal

growth short. Such trees are usually stunted and produce few fruits.

Figure 72.—T^wo-year-old peach trees: Ay Adequately supplied with nitrogen and

potassium; B, adequately supplied with nitrogen. The narro^vness of the leaves

and their tendency to fold are evident at the tips of the branches in B.

Cherry.—In July or August the older leaves of affected trees turn lighter

green than those of normal trees and their margins roll upward. At the same

time the leaf margin becomes discolored and the faded areas develop into

necrotic, scorched lesions. Severely affected trees are apt to have small leaves

and short terminal growth, to be stunted, and to produce few fruits.

Plum.—In New York the general symptoms on plum are similar to those

described by Wallace (317). In the spring and early summer leaves of

potassium-deficient trees appear normal except for being somewhat small.

In July or August (depending largely on weather and degree of deficiency)

the leaves on peripheral branches begin to lose their normal green color,

usually fading first at the margins. As chlorosis progresses, the margins of

the older leaves roll inward toward the upper surface. Finally marginal

necrosis occurs. On severely affected trees almost all the leaves show a progressive development of symptoms. On moderately affected trees only the

older leaves on outside branches may show the symptoms in all stages. On

slightly affected trees the symptoms may develop late and on the outer

branches only; they may not develop beyond the leaf roll stage. Cumulative

effects of severe scorch are decreased terminal growth, delayed fruiting of

young trees, and marked dwarfing (pi. 24, E).
VIRUS DISEASES OF STONE FRUITS 227

In California dieback of branches, as well as leaf chlorosis (pi. 24, D), is

a symptom. Heavy bearing usually makes the symptoms more conspicuous,

and some plum trees may not show symptoms until they come into bearing.

Plum trees on peach rootstocks are injured more than those on myrobalan plum

(P. cerasifera) rootstocks. Leaves of trees that show symptoms contain less

than 1 percent of potassium (dry-weight basis).

Control Measures

Prune, peach, and cherry trees with potassium-deficiency symptoms responded to applications of potassium fertilizers when they were growing on

soils ranging from sandy to silty clay loams with or without well-drained subsoils (275). Applications of potassium chloride (muriate of potash; commercial 5 0 to 60 percent) at rates of 1 to 5 pounds per tree, depending upon

its age, resulted in satisfactory recovery after 1 to 3 years. Fresh hay or

straw mulch and manure also effectively reduced or eliminated potassiumdeficiency scorch.

In California improvement was obtained with heavy applications of potash

both when fruit was thinned early and when it was not thinned. Usually lowpotassium areas in orchards are replanted to more tolerant crops. According

to analyses of the soil by the Neubauer (rye-seedling) method, such soil areas

contain less than 100 parts per million of potassium in the first 4 inches of

soil (299).

In orchards planted on sand, clay, or gravelly loam in the Coastal Plains,

peach trees responded to application of potash fertilizer (284, 310). Excellent results were obtained in a single season in Maryland from an application

of 3 pounds of potassium nitrate containing 43 percent potash on 7-year-old

trees. This fertilizer served as a source of nitrogen and potash. Equally good

growth and recovery from potassium deficiency of young trees were obtained

when 1 to 2 pounds of potassium chloride to the tree was broadcast on the

surface of the soil.
PHOSPHORUS DEFICIENCY

By F. P. CuLLiNAN and O. W. DAVIDSON

Geographic Distribution and Economic Importance

Disorders of stone fruits that might be caused by lack of available

phosphorus have not been as numerous as those caused by lack of some other

nutrient and trace elements. It is known that phosphorus is relatively low

in some soils in the stone-fruit-producing districts of the country. On these

soils annual crops frequently show marked symptoms of phosphorus deficiency,

and their production is limited if phosphate fertilizers are not added. Certain

soils in California have a low content of available phosphorus and a high

capacity for the fixation of this element. Eighteen different annual crops

tested on one of the soils, an Aiken clay loam, in California failed to make

satisfactory growth without the addition of phosphate fertilizer. When

phosphate was added, however, there was no improvement in the growth and

the yield and quality of fruits of almond, cherry, peach, prune, and other

fruit trees established on this soil. Both treated and untreated trees were

comparable with trees growing on more fertile soils in California (301).

Improvement in growth and yield of peach trees planted on a coarse phase

of Norfolk sand typical of much of the sand-hill section of the Southeast was

reported in South Carolina. When no phosphorus was added, the trees showed

symptoms of phosphorus deficiency, but the deficiency symptoms were not as

marked as those on trees on the same soil that had received phosphorus and

nitrogen but no potassium (312). Typical potassium-deficiency symptoms

were evident on them. While the omission of phosphorus in these experiments

did not result in marked deficiency symptoms, lack of phosphorus was reflected

in reduced growth and yield.

Similarly, peach trees on sandy soils in New Jersey have shown phosphorusdeficiency symptoms. Lack of adequate phosphorus was reported to be

responsible for considerable losses to peach growers each year (285).

Stone-Fruit Species Affected

Phosphorus deficiency has been reported and described largely for peach

(Pnmus pérsica).

Symptoms

When peach trees are grown in sand culture, the first symptom is the development of a dark-dull-green to purplish-green color of the leaf. This

abnormal color contrasts with the bright green of trees adequately supplied

with nitrogen. The leaves show no puckering or crinkling along the midrib,

and the blade is narrower than normal for the variety, leathery, and flat

(ñg. 70, A). When the phosphorus shortage is severe, the veins on the

under side of the leaf and the leaf petiole may have a purplish color.

In New Jersey a compound deficiency of phosphorus and potassium has

been observed to be second only to a deficiency of nitrogen in frequency of

occurrence (28J), This deficiency often occurs in young peach plantings on

acid coastal plain soils. The symptoms exhibited by the affected trees range

from those of a mild deficiency of one of these nutrients and a severe deficiency

of the other to those of severe deficiencies of both. The trees develop a hard

228
VIRUS DISEASES OF STONE FRUITS 229

type of growth with relatively slender and abnormally pigmented leaves. In

many instances they resemble nitrogen-deficient trees; in fact, they usually

can be stimulated to make an improvement in growth for 2 or 3 weeks by

heavy application of sodium nitrate or ammonium sulfate. It is possible, however, that this response is due primarily to the liberation of some potassium from

the soil complex by the added cations.

Leaves on the older portions of the current-season growth droop, unlike

those on normal peach trees. Young, bearing trees affected with this compound deficiency, if they set at all, produce small, dull-red fruits that are

abnormally astringent. These characteristics, together with the small, rolled

foliage formed on the trees, suggested many years ago the term "false little

peach" for this condition.

Control Measures

Where phosphorus-deficiency symptoms have been observed under field conditions, the trouble has been corrected by application of phosphate fertilizers.

Good soil-management practices, including the use of cover crops fertilized to

produce a good tonnage of green manure when turned under, aid in building

up the available phosphorus content of the soil.
IRON CHLOROSIS

By J. P. BENNETT

Geographic Distribution and Economic Importance

Iron chlorosis (lime-induced chlorosis) is widely distributed over the

western half of the United States {274, 292), It is of economic importance

in every State lying partly or wholly west of the 98 th meridian. The areas

involved receive relatively low annual rainfall as compared with the eastern

half of the country, where the soils are usually acid and chlorosis is rare. So

far as known chlorosis in the field is limited to calcareous soils, in which iron,

although abundantly present, is relatively unavailable because of their high

pH. Increasing the water content of such soils by irrigation or spring rains

aggravates the tendency toward chlorosis probably by raising the soil pH.

Cause and Order of Susceptibility of Stone Fruits

Plants vary widely in susceptibility to iron chlorosis induced by high soil

lime. The cause of susceptibility is not definitely known, but susceptibility

seems to be related to the iron requirement, extent of the root system, and the

activity of the roots as indicated by respiration. Many economic plants have

been practically grouped according to the amount of lime which they will

tolerate without becoming chlorotic; this amount is generally lower in light

than in heavy soils. The tolerated concentrations range from 1 to 5 percent

for the most susceptible species on the Hghtest soils up to 15 to 20 percent

or even higher for the less susceptible species on heavy soils.

The order of susceptibility of the stone fruits on the basis of tolerance to

lime is peach (Prunus pérsica), sweet cherry (P. avium), plums (P. domestica,

P. salicina), apricot (P. armeniaca), and almond (P. amygdalus) if they are

on the roots of their own species. The rootstock is in general the dominant

factor in susceptibility. Thus apricot or plum on peach roots are very

susceptible, but on plum roots they are much less so. Trees on apricot and

almond roots are also much less susceptible than those on peach roots. As

compared with roots, the tops have httle apparent relation to susceptibihty

although to a large extent they determine the iron requirements of trees. Sour

cherries are affected with iron chlorosis in Utah {315a),

Symptoms

The principal symptom of iron chlorosis is deficiency of chlorophyll {271,

298) in the leaves (ñg. 73), It is commonly imderstood that slightly to

completely yellow leaves are chlorotic, but probably degrees of chlorophyll

deficiency which show as lighter than normal shades of green rather than as

yellowness also are indicative of iron deficiency. On leaves which are distinctly

yellow the color pattern may vary from complete absence of greenness to

slight yellowness between the larger veins. A common symptom is a distinct

band of green along the veins, shading to yellow in the interveinal regions

(pi. 25, E). None of the color patterns are specific for iron chlorosis; all

may be found on leaves chlorotic from other causes such as potassium or

magnesium deficiency.

The most distinctive characteristic of iron chlorosis is that it appears first

and is most developed at the tips of growing terminal shoots. Older leaves

230
VIRUS DISEASES OF STONE FRUITS 231

Figure 7}.—Leaves of French (Agen) prune showing the normal green and the characteristic color patterns in reduction of chlorophyll due to lack of available iron.

are successively less chlorotic, and basal or spur leaves may be normally green.

In succeeding seasons, unless remedied by treatment or more favorable soil conditions, iron chlorosis appears earlier and is more severe. Chlorosis may eventually affect not only the leaves at the base of the shoots but also those on

spurs and other slow-growing branches. On trees affected with iron chlorosis

the leaves are chlorotic when formed. They may subsequently become green

if iron becomes available; when once fully green and fully grown, leaves do

not become chlorotic as a result of iron deficiency, because the iron in leaves

is highly immobile. Most of the chlorophyll is formed during the early part

of the season but it generally increases further during the remainder of the

season except in severely affected leaves. If iron chlorosis is light to

moderate, the leaves are usually of about normal size and without lesions.

But in severe cases leaf size is usually reduced and areas of dead tissue often

occur along leaf margins or between the larger veins. Severe cases usually

result also in shorter shoot growth and even in dying of shoots from the

tips downward.

Control Measures

The control of iron chlorosis depends on making more iron available (270,

292, 318, 320). This can be accomplished by spraying, injection, or soil treatment. With all treatments, including spraying, applied during the leafy season, the response becomes slower as the season progresses until little or no

effect is obtained from those made during the latter half of the season.

Spraying with dilute ferrous sulfate, usually of less than 1-percent concentration, is effective; but the effect lasts for only one season and spraying

must be repeated during that season to include developing shoots.

Treatment by injection is done by boring holes into the live wood of the
232 HANDBOOK 10, U, S. DEPARTMENT OF AGRICULTURE

branches or the trunk or preferably in the base of the trunk or the upper

part of the root below ground level, where the sapwood is thicker and healing

of wounds occurs most rapidly, at intervals of 4 to 5 inches around the tree

in order to get adequate distribution. A quantity of a soluble iron salt (2 to

5 gm.) is placed in each hole, which is closed by wax or a plug. Ferric citrate

and ferric oxalate have been found to be especially suitable, because of the ease

of handling them; but any soluble iron salt not otherwise toxic is effective.

Soil treatment is accomplished by digging trenches or boring auger holes

around the tree and putting a suitable quantity of a soluble iron salt (usually

ferrous sulfate) in the bottom of each trench or hole. The salt must be

brought into contact with the roots to be effective; therefore holes or trenches

should reach to the root zone and should be placed to give distribution around

the tree. Subsequent watering aids in obtaining contact between the salt and

the roots.

With both injection and trench or auger-hole treatments there is danger

of killing considerable tissue, not only by the tools but by the high concentration of the salt used. Cures effected by these methods will last about

3 years if the maximum dosage that does not produce excessive injury is

used. The treatments give the best results when applied during the dormant

season, but they may be used when leaves are present. There is some danger of

injury to the leaves, however, if large doses are used.

Permanent cure of iron chlorosis appears to require lowering the general

level of the soil pH to a point at which plants are able to get sufficient iron by

normal processes, whatever these may be. In highly calcareous soils this is

not feasible or economically possible. Because of the aggravating effect of

increased water content, better drainage and less frequent watering often

improve the condition of plants. In light soils with a low lime repeated light

surface applications of ferrous sulfate or sulfur or large apphcations of organic

matter may give extended benefit. Permanent cover crops of nonsusceptible

varieties appear to aft'ord continued control whenever they can be used.
MAGNESIUM DEFICIENCY

By A. LEON HAVIS

Geographic Distribution and Economic Importance

Disorders in stone fruits attributable to magnesium deficiency in the soil

Figure 74,—Leaves from a peach tree gro^vn in a magnesium-deficient nutrient solution: A, Severe symptoms; B and C, mild symptoms.

233
234 HANDBOOK 10, U, S. DEPARTMENT OF AGRICULTURE

have not been reported from most of the stone-fruit districts of the country.

It is known, however, that apple orchards in northeastern United States have

responded to the addition of magnesium to some soils {27d). It is not known

whether apple trees are more sensitive to magnesium deficiency than stone

fruits, but in an orchard on Chillum gravelly loam at Beltsville, Md., apple

and pear trees (2^^) showed typical symptoms of magnesium deficiency on

leaves, whereas adjacent peach trees on the same soil did not. In New Jersey

magnesium deficiency is reported to occur occasionally after heavy rains in

peach orchards grown on light sandy soil. In wet seasons the deficiency has

been found on peach trees growing on very acid loams and on sandy loams

receiving heavy applications of lime of low magnesium content {ll'y^.

Losses due to magnesium deficiency may result when defoliation is severe.

In New Jersey winter mortality of trees occurs where peach trees lose many

leaves and are weakened from the effects of magnesium deficiency {!%')),

Losses due to magnesium deficiency have been insignificant in the Western

States.

Stone-Fruit Species Affected

Magnesium deficiency has been noted on peach {Prumis pérsica).

Symptoms

When peach trees are grown in a magnesium_-deficient nutrient solution,

the older green leaves may develop light-gray- or fawn-colored spots in the

area between the veins. In severe cases the spots may enlarge and take in the

edges of the leaves (fig. 74). In early stages leaves may show a chlorosis

somewhat like the early stages of iron chlorosis. The leaves of severely affected trees shed, from the base toward the tip, and only a few of the youngest

leaves may remain near the growing tip. As the green color fades out between

the veins, the leaf tissue takes on a papery gray appearance and the dead spots

may enlarge and envelop the outer margin of the leaves (pi. 2 5, JF). Under

controlled nutrient tests in sand culture magnesium deficiency appears first

where calcium or potassium is relatively high in relation to magnesium.

Control Measures

Applications of magnesium sulfate at the rate of 1 pound per tree should

correct the mild cases of magnesium deficiency observed on peaches in sandy

soils. Spraying the leaves with a solution of epsom salts in water may give

a quicker response.
MANGANESE DEFICIENCY

By OMUND LILLELAND

Geographie Distribution and Economic Importance

Manganese is one of the trace elements, or micronutrients, required in

relatively small amounts by all plants. Mild chlorosis of leaves caused by

manganese deficiency has been observed on stone fruits in California, Utah,

Michigan, and New York. A number of unpubhshed observations of

chlorosis suspected of being caused by lack of manganese have been made in

several peach-producing districts of eastern United States.

The amount of injury to trees or loss of crops has in general been negligible.

In Cahfornia in one orchard that was severely affected and chlorotic a crop of

only 3 tons to the acre was harvested instead of a 10-ton crop that would

be expected on trees of the same age with healthy foliage {291). DefoUation seems to be rare, and no evidence of dieback has been observed. It seems

unUkely that manganese deficiency will cause any serious effects in commercial stone-fruit orchards, because it is easy to correct.

Stone-Fruit Species Affected

Manganese deficiency has been observed on almond {Primus amygdalus),

apricot (P. armeniaca), sweet cherry (P. avmm), sour cherry (P. cerastis),

peach (P. pérsica), domestica plum (P. domestica), and Japanese plum (P.

salicina ).

Symptoms

A distinct pattern has been observed on the leaves of all stone-fruit species

on which manganese deficiency has been observed. The midrib and main

veins with adjacent bands of tissue of varying width remain green, whereas

the interveinal and peripheral areas of the leaf edges may be chlorotic (pi.

25, A-D). All the leaves on some severely affected trees may show some

degree of chlorosis, but on other trees only a few branches may be involved.

Leaf scorch may occur when the deficiency is severe. There are no marked

symptoms recognizable on the fruits or twigs.

Samples of leaves of peach taken from 39 Elberta orchards and analyzed

for manganese content showed a range of 293 to 6 p.p.m. (parts per million)

on a dry-weight basis. Deficiency s^^mptoms on peach generally seemed to

be associated with a manganese content of less than 17 p.p.m. The changes

in manganese content throughout the summer were not large, and it was

concluded that samples of leaves taken at any time from June to October in

California would reflect the general level of manganese in peach trees {291).

Analyses of chlorotic leaves of 6 kinds of fruits, including peach, almond,

prune, and sweet cherry, gave values ranging from 5 to 2 5 p.p.m. of

manganese. Differences in content could not be correlated with species.

Control Measures

Manganese deficiency is easily corrected by use of leaf sprays in early summer (5 to 10 pounds of manganese sulfate in 100 gallons of water). Injection of a manganese sulfate solution into the branches and soil treatments with

manganese sulfate are also effective. In a severely chlorotic orchard in California a 1-percent solution of manganese sulfate was sprayed on certain

235
236 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

branches in the spring and in 2 weeks the sprayed branch on every tree was

normal, while the rest of the tree was chlorotic. Similarly, in New York

D. Boynton injected dry manganese sulfate into the branches of chlorotic sour

cherry. The following spring the treated branches bore normal green leaves,

whereas the untreated ones bore chlorotic leaves (pi. 2 5, C, D).
ZINC DEFICIENCY

By W. H. CHANDLER

Geographic Distribution and Economic Importance

In the hot interior valleys of the Pacific slope, stone-fruit trees are apt to

show zinc-deficiency symptoms on sandy soils, especially if cultivation is

frequent during the summer. Old sweet cherry trees are apt to show such

symptoms even on loams or clay loams. At one time the losses from decline

of trees and reduction in crops amounted to millions of dollars. Even in

orchards that have not had zinc apphcations losses from zinc deficiency have

been greatly decreased by the general reduction in summer cultivation; the

decrease is possibly due to soil shading by weeds that are permitted to grow.

Zinc deficiency has been reported on stone fruits in Utah, Idaho, and

Colorado in addition to the Pacific Coast States and British Columbia, Canada.

It seems likely that it might be found on these fruits in all 11 of the Western

States, since it has been reported to occur on other trees in that region. In

general, zinc deficiency has occurred on sandy soils or on those treated with

large amounts of organic matter. In some of the Western States disorders

shown to be due to lack of available zinc were observed first on sites formerly

used as corrals or other enclosures for livestock. In the Pacific Coast States

the deficiencies are confined largely to the irrigated valleys of the interior.

In the Mountain States deficiency of zinc has also been observed in irrigated

valleys. Up to the present time zinc deficiency has not been reported on stone

fruits in the eastern half of the country except in New Jersey (282a) and

Florida. In Florida (286) it has been found in peach orchards growing on

Norfolk fine sand. Unpublished observations indicate that zinc deficiency

may occur on peach elsewhere in the East.

Susceptibility of Stone Fruits

Chandler (280) listed sweet cherry (Prtintis avium) as the most susceptible

of the stone fruits to zinc deficiency. Other stone fruits affected, in order

of susceptibility, seem to be Japanese plum (P. salicina), domestica plum (P,

domestica), peach (P. pérsica), apricot (P. armeniaca), and almond (P.

amygdalus). In Utah zinc-deficiency symptoms have been observed in sour

cherry (P. cerasus) (315, 321).

Symptoms

Leaf symptoms have been emphasized more than others. Irregular splashes

of yellow occur between the veins, especially on leaves of the new growth in

the first few weeks of spring and on long shoots during the last few weeks of

summer. Most of the leaves have wider green areas along the veins and around

the yellow splashes than manganese-deficient leaves have, and the yellow tends

to be paler and less golden. Leaves at the end of some summer shoots may be

creamy yellow, with very little green even along the veins. Leaves that

develop in the first few weeks of spring at the apex of a long shoot of the preceding year may be very much smaller than normal (about 1 inch long and

54 inch wide or less), nearly sessile, and stiff; the disease has been known as

Uttle-leaf (281, 282, 286, 297). The small, stiff leaves are crowded very closely

into tufts (ûg. 75). Because the internodes are very short, the disease is some237
238 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

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Figure 75.—Young peach tree showing typical rosette condition accompanying zinc

deficiency, Utah.

times called rosette (pi. 26, A-C). The branches may die back so much in

late summer that few if any rosettes grow in the following spring, the upper

shoots being water sprouts from dormant buds below the dead parts.

Such dying back of zinc-deficient cherry trees is so general that spring

rosettes are rarely seen (fig. 76). Leaf mottling and very small fruits on

the outer parts of branches may be the only distinctive symptoms of serious

zinc deficiency.

Old almond trees may not show a distinct mottling of the leaves, and

the leaves may have only a paler than normal color. Because bearing trees

are pruned so little and make such short shoot growth, rosettes as well as

distinct mottling are apt to be seen in early summer on water sprouts of the

preceding year only. Young, vigorous, zinc-deficient almond trees, however,

may show mottling and rosettes much like those on Japanese plum.

On trees of all affected species of stone fruit, the internodes of the last few

inches of the longest summer shoots may be very short and the leaves may

be rather small, yellowish, often much distorted, and closely packed.

In peach, apricot, plum, and cherry orchards, the most dependable zincdeficiency symptoms occur on the fruits if the deficiency is not bad enough

to prevent all fruits from setting. Fruits on the lower parts of the trees
VIRUS DISEASES OF STONE FRUITS 239

may be normal or nearly so. Those in the tops, and especially toward the

ends of the branches, tend to be progressively much smaller than normal (pi.

26, C). In California at least, this progressive decline in size of fruits toward

the ends of the upper branches seems always to be conclusive evidence of zinc

Figure 76.—Sweet cherry tree showing production of small, chlorotic leaves and severe

dieback, caused by zinc deficiency, Utah.
240 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

deficiency. The fruits also tend to be abnormal in form. Those of peach and

Japanese plum, are more flattened than normal and constricted below the

apex into a rather thick neck with a terminal beak. Apricot fruits are less

flattened than normal, more nearly round, and grading downward in size to

that of medium-sized cherries. Mature peaches from zinc-deficient trees

break down or turn brown sooner after harvest than those from normal trees.

Control Measures

Most soils have great capacity to render zinc unavailable to trees. In some

of the Pacific slope soils this fixing capacity is so great that 1,000 to 1,5 00

pounds of zinc sulfate applied to an acre of soil may not supply the necessary

ounce or two of zinc to an acre of trees. Soil appUcations are therefore

avoided as much as possible.

Leaf spraying with zinc-Hme has not been very eflfective on deciduous

trees. Dormant spraying with zinc sulfate alone, 10 to 5 0 pounds of zinc

sulfate to 100 gallons of water, has been found to be the best practice that

has been tried for peach, almond, and Japanese plum. The amount required

depends upon the severity of the symptoms. If there is much dying back,

even more than 50 pounds to 100 gallons may be advisable in dormant applications. If the zinc is applied in combination with bordeaux mixture against

leaf curl or other diseases controlled by winter spraying, somewhat more zinc

sulfate should be used because of the effect of the lime in the bordeaux

mixture. Apricot does not respond so well as peach to dormant spraying, and

therefore stronger solutions must be used. Sweet cherry trees hardly respond

at all to spraying, unless the soil is one with such a low fixing power that

soil treatment (5 00 pounds of zinc sulfate or less to the acre) is feasible.

Driving very many zinc-coated finishing nails into the trunk and branches,

with the heads driven to the bark, may be the only treatment. As many as

40 to 50 zinc-coated, 1-inch-long nails for each inch of trunk circumference

may be required; no nail should be nearer than a half inch to another, or the

bark may be killed between them. And, of course, the nails should be rather

well distributed around the trunk or branch. Great masses of gum will

exude around each nail, but this seems to do no harm unless the nails are too

close to each other.
COPPER DEFICIENCY

By CARL J. HANSEN

Geographic Distribution and Economic Importance

Copper deficiency (exanthema) was first reported on plums in California

by Smith and Thomas (313) in 1928. Since then additional affected plum

trees have been found in a few localities in the State. Other stone fruits

have not been definitely proved to be suffering from copper deficiency in

California. However, in a few former corral areas, where other complications would obscure symptoms of copper deficiency if it were present, peach,

cherry, and apricot have in some instances responded to applications of copper.

Copper deficiency has not been reported on stone fruits in eastern United

States, but deficiency of copper in Florida soils has been shown to affect citrus

(279).

Stone-Fruit Species Affected

Only plums (Prunus domestica and P. salicina) are positively known to

be affected with copper deficiency in this country. In South Africa copperdeficiency chlorosis has been observed on apricot (P. armeniaca) and peach

(P. pérsica) (269).

Symptoms

The tips of the shoots of the affected varieties of domestica and Japanese

plum are killed, and the lateral buds are forced into growth. These lateral

shoots may in turn die back as illustrated by the Imperial prune shoots in

plate 26, D. The chlorosis and scorching of the Late Santa Rosa plum leaves

shown in figure 77 have been identified as symptoms of copper deficiency.

The trees affected were cured by applying copper sulfate to the soil. Some

other varieties of plums, at least under the particular climatic and soil conditions where they were observed, showed none or practically none of the leaf

symptoms. The leaves, for example, remaining on the two shoots in plate 26,

D, are practically normal, although some scorch was observed on those that

had fallen. The bark of some small branches of affected trees may be rough

and corky, but the extent of such injury depends on the variety. Swellings

may also occur in the regions surrounding the buds and the lateral shoots.

In many respects the copper-deficiency injury illustrated in plate 26, D,

resembles the injury caused by excess boron. Copper deficiency, however,

does not produce corky areas on the leaf petioles and veins and does not cause

injury to the stems just above the buds.

Control Measures

Plum trees showing symptoms of copper deficiency have been cured by

application of copper sulfate to the soil, by injecting copper sulfate into

holes bored in the trunks, and by spraying the young leaves with 5-5-5 0

bordeaux mixture.

Soil apphcations have generally varied from 1 to 5 pounds of copper sulfate

placed in the bottom of a circular trench or spaded in around the base of each

tree, the exact quantity depending on the size of the tree and the fixing

power of the soil. In a few soils with a high fixing power even considerably

heavier applications were not effective.

891793°—51—19

241
242 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Figure 77.—Leaves of Late Santa Rosa plum showing chlorosis and scorching characteristic of copper deficiency.

The holes used for the injection of dry copper sulfate are spaced about 4

inches apart around the trunk, and excessive injury is avoided by keeping the

material away from the cambium and the bark. This is done by inserting the

copper sulfate in gelatin capsules or forcing it through a tube. Wooden plugs

are generally driven into the holes.

It is likely that more copper deficiency would occur if most stone-fruit

trees were not regularly sprayed with copper sprays for disease control.
CALCIUM DEFICIENCY

By A. LEON HAVIS

Geographic Distribution and Economic Importance

In the fruit-producing districts of this country no serious disorders in top

growth of stone fruits that could be attributed to lack of calcium have been

reported. In the humid region of the eastern part of the country a number

of soils are acid, and satisfactory growth of many plants on these soils is

obtained only when lime is added to correct the acidity and raise the pH.

Many soils have been made productive, particularly for legumes, grasses, and

cereal grains, when lime and phosphate were added as fertilizers. On many of

the soils on which peach and other stone fruits are grown the soil is frequently

acid and low in calcium. Tree fruits are known to tolerate acid soils. Calcium

is an essential element required by all plants; stone fruits are not an exception. The appearance of deficiency symptoms under field conditions, however, is not marked. The addition of lime to soils low in potassium and

magnesium may produce deficiency symptoms of the last two elements. The

stone-fruit-producing districts of the Western States have alkaline soils, and

no symptoms of calcium deficiency have been reported on stone fruits.

Stone-Fruit Species Affected

Peach {Prunus pérsica) is the only species known to suffer from calcium

deficiency in orchards.

Symptoms

When peach trees are grown in a nutrient solution lacking calcium, the

first symptom of the deficiency is usually decreased terminal growth; the

older leaves may be of normal size, but the young leaves are usually smaller

than normal. The color of the leaves is dark green, and no chlorosis is

evident. Later, a large chlorotic area develops in the center of some of the

younger leaves. It is a large, characteristic spot involving tissue on either

side of the midrib. The older leaves later show marginal chlorosis and breakdown (pi. 27, A), Finally the leaves drop off at the tip; then the ends of

the shoots may die back. Under controlled nutrient conditions calcium

deficiency is shown in peach foliage first where potassium and magnesium

are relatively high.

In the field calcium deficiency has been reported to curtail greatly root

extension of peach (285).

243
BORON DEFICIENCY

By CARL J. HANSEN, F. P. CULLINAN, and E. L. PROEBSTING

Geographic Distribution and Economic Importance

Boron is one of the elements essential to all plants, but the amount required is relatively small when compared with some of the other essential

elements. A trace is needed in nutrient solutions for satisfactory growth of

some plants, but only a few parts per million more than needed for optimum

growth may be toxic to other plants. In some of the irrigated districts of

the West the concentration of boron in the irrigation water may be high

enough to cause injury to stone fruits.

Boron deficiency on apricot and peach has been reported in virgin soils in

British Columbia, Canada, (29la, 304) and in commercial orchards in the

Northwest (285). It is known to occur on apple in northeastern United

States, principally in New York and the New England States. Internal cork

of apple found in orchards in the Cumberland-Shenandoah Valley (305) and

New York (278) has been corrected by injection of boric acid crystals or

application of boric acid to the soil. Apple orchards in southwestern Michigan

also have been improved by application of borax. Even though boron is

known to be deficient in soils in eastern United States, there have been no

reports thus far of marked boron deficiency on stone fruits. Some breakdown in the flesh of peach fruits has been suspected of being due to lack of

boron, but thus far correction of this trouble has not been effected by application of borax.

Boron deficiency has been observed on domestica plums in the Sierra

Nevada foothills of California (294). The orchards were on soils of the

Aiken and Sites series.

In orchards in the vicinity of The Dalles, Greg., a dwarfed, chlorotic condition has been observed on the leaves of cherry, peach, prune, and apricot.

The trouble was most noticeable on sweet cherry. The symptoms, which

were in general characteristic of zinc deficiency, disappeared after the trees

were sprayed with zinc sulfate, but better results were obtained when boric

acid was added to the spray solution (311).

In nutrient-culture experiments v^^ith apricot in California deficiency

symptoms developed when the boron concentration of the nutrient solution

was 0.1 p.p.m. (parts per million). The trees showed leaf injury and dieback.

When the concentration of boron was raised to 0,5 p.p.m., growth was resumed

and 6 weeks later no evidence of boron deficiency was noticeable (297).

Stone-Fruit Species Affected

Domestica plum (Prunus domestica) varieties President, Giant, and Diamond are the only plums in California that up to now have shown symptoms

of boron deficiency. Varieties of Japanese plum (P. salicina) growing

adjacent to affected domestica plums appeared normal. Peach (P. pérsica)

is naturally affected with boron deficiency and has been experimentally

affected. Apricot (P. armeniaca) y sweet cherry (P. avitcm), and cherry

seedlings also are affected,

244
VIRUS DISEASES OF STONE FRUITS 245

Symptoms

The only boron-deficiency symptoms that appear consistently on plums in

CaUfornia orchards are on the fruits. Brown sunken areas in the flesh may

consist of a single spot or may involve practically the whole fruit. The

flesh beneath the sunken parts is brown and firm, and in severe cases the

browning extends to the pit. The fruits color earlier than normal fruits and

drop. The number of fruits on a tree showing these symptoms may vary

from a few to the entire crop. Leaves from trees showing deficiency symptoms in the fruit contained 25 p.p.m. or less of boron, whereas leaves from

normal trees contained 3 0 p.p.m. or more. Leaf concentrations ranging from

26 to 29 p.p.m. were obtained from both normal and deficient trees.

In British Columbia the outstanding symptoms of boron deficiency on

peach are failure of buds to break in the spring and dying of twigs, branches,

and sometimes even entire trees (304). When peach is grown in a nutrient

solution lacking boron the first symptoms appear at the terminals of upright

shoots or at the end of the leader. The terminals die back, dark-green watersoaked spots appear in the bark, gum may exude, lateral buds develop, and the

resulting new shoot growth also dies back. Small irregular spots appear in

the leaf, die, and drop out. Most of the affected leaves are chlorotic. Injured

leaves fall off rapidly from the tip toward the base (322), On the stems

dark-brown, corky spots appear (289y 322). Cherry and peach seedHngs in

sand cultures made good growth when the concentration of boron in the

nutrient solution was 1 p.p.m. Both of these fruits showed injury when

the concentration was 5 p.p.m. {289). In British Columbia, however, twigs

from peach trees that showed signs of boron deficiency had a boron content of

4 to 8 p.p.m. {304).

In the Northwest the apricot shows the following fruit symptoms {277a) :

Internal browning and corky tissue developing in the stone area; cracking,

shriveling, surface browning, and constrictions.

Control Measures

Boron-deficiency symptoms on plums disappeared when borax was broadcast on the surface of the soil in late summer at the rate of 0.5 pound to the

tree, or approximately 50 pounds to the acre. It is estimated that the effect

of a single application may last 3 years. Some boron injury occurred when

borax was used at the rate of 1 pound to the tree {294). Applications of

0.5 pound of borax per tree have corrected boron-deficiency symptoms on

apricots.
BORON-EXCESS INJURY

By CARL J. HAKSEN

Geographic Distribution and Economic Importance

Injury to stone fruits by an excess of boron has occurred in approximately

one-fourth of the counties of CaUfornia. The districts where boron injury

has been reported are scattered mostly in the western part of the State. They

consist of single orchards irrigated by a well high in boron or of several

orchards. Excess boron has sometimes been found occurring naturally in

the soil where irrigation is not practiced (288, 290).

Stone-Fruit Species Affected

Almond (Prtmîts amygdalus)^ apricot (P. anne/iiaca) y sweet cherry (P.

avhim), peach (P. pérsica), Japanese plum (P. salicina), and domestica plum

(P. domestica) are known to be injured by excess boron.

Symptoms

Many kinds of plants show marginal leaf scorch when grown in soil containing excess boron, but this scorch does not occur on apricot, peach, plum,

cherry, and almond. On plum, apricot, peach, and almond the principal

injury is to the shoots of the current-season growth. The French (Agen)

prune shoot in plate 27, B, shows how the shoots die back at the tip and the

cracked, corky bark, a symptom of the excess. Sometimes gum may also be

exuded from the injured parts. The short section of a shoot illustrates the

tendency for the injury to be most severe just above the buds. Corky areas

similar to those on prune petioles and on the large veins of the lower side of

prune leaves (pi. 27, B) are also found on apricot (fig. 78). On peach and

almond the leaf injury is limited to the midribs. If other conditions are

normal for growth, the lateral buds on injured apricot, plum, and peach shoots

start to grow, only to be killed back later. When apricot trees are dormant,

the injured branches look like the shoots shown in figure 79. Enlargements

like those at the nodes do not appear on peach. Cherries are injured by too

much boron, but symptoms such as those just described are rarely found.

Cause of injury can be determined by analysis of soil and plant parts and by

observation of typical symptoms on nearby plants {293),

Injury sometimes occurs on fruits of peach and occasionally on those of

apricot. The injured areas on the peach fruits are dark brown and woody;

they vary in size, but a single one may involve over half a fruit and extend

from the surface almost to the pit. The injury on apricot fruits consists of

dark, circular areas approximately % inch in diameter.

Control Measures

Unfortunately there is no cure for excess boron except the adequate use

of satisfactory irrigation water.

246
VIRUS DISEASES OF STONE FRUITS 247

Figure 78,—Apricot shoots injured by excess boron, showing dieback at tips and

cracked and corky bark.
248 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Figure 79.—Dormant apricot shoots, showing at nodes enlargement caused byexcess boron.
Agriculture Handbook 10, U. S. Department of Agriculture PLATE 23

A, Peach trees showing symptoms of nitrogen deficiency; B, peach tree showing symptoms of potassium deficiency;

C and D, comparable normal trees.
Agriculture Handbook 10, U. S. Department of Agriculture PLATE 24

A and B, Peach shoots from orchard trees showing rolled leaves characteristic of potassium deficiency; C, portion

of potted peach grown with low potassium, showing marginal scorch of leaves; Dand E, prune leaves and

branch showing symptoms of potassium deficiency.
Agriculture Handbook 10. U. S. Department of Agriculture PLATE 25

A, Peach leaves showing a gradient of manganese-deficiency symptoms; B, sour cherry leaf showing manganesedeficiency symptoms, Michigan; C and D, sour cherry leaves (C) from a manganese-deficient branch and (D)

from a branch cured by injection of manganese sulfate, New York; E, prune leaves showing symptoms of iron

deficiency, in contrast with normal leaves; F, peach leaves showing symptoms of magnesium deficiency.
A-C, Plant parts showing symptoms of zinc deficiency, in contrast with healthy ones at right: A, Peach; B, apricot; C, cherry. D, prune shoots show:

of copper deficiency.

ng symptoms >

n
Agriculture Handbook 10, U. S. Department of Agriculture PLATE 27

A, Peach leaves showing symptoms of calcium deficiency. B, French prune twigs showing symptoms of boron

injury. C and D, Leaves showing symptoms of sodium injury: C, Apricot; D, peach. E and F, Peach leaves

and shoots showing symptoms of arsenic injury.
SODIUM-EXCESS INJURY

By OMUND LILLELAND

Geographic Distribution and Economic Importance

Injury of stone fruits due to excess sodium is widely distributed throughout the San Joaquin Valley and in other fruit-growing districts of California.

In some localities only one or two trees are aííected in a 20-acre orchard,

whereas in others the entire orchard may be affected.

Stone-Fruit Species Affected

Almond {Vrunus amygdahs), apricot (P. armeniaca), sweet cherry (P.

avhtm), peach (P. pérsica), and Japanese plum (P. salicina) are known to be

injured by excess sodium.

Symptoms

Several types of leaf scorch (300, 302) are attributable to injury caused

by excess sodium. Burning at the tip of the leaf is frequently characteristic

of early stages of injury (pi. 27, C, D). Trees may be reduced in growth,

but remain alive for a number of years, or they may die in one season. Analysis of scorched leaves often shows 0.5 percent or more of sodium in the dry

matter. A low potassium content is frequently associated with a high sodium

content. Chemical analysis of the roots of injured trees reveals accumulation of sodium in the wood. Injury may occur on soils which contain as

low as 2 Í 0 parts per million of total soluble salts.

Control Measures

Leaching the soil with nonsaline irrigation water and additions of gypsum,

sulfur, and similar materials, depending upon soil conditions, are suggested

as corrective measures.

249
ARSENIC INJURY

By C. P. HARLEY

Geographic Distribution and Economic Importance

In the Pacific Northwest, principally in central Washington, it has been

known for some time that certain crops planted on old apple-orchard sites

make poor growth or none at all. The cause of this is the accumulation in the

soil of arsenic residues as a result of spraying with arsenical insecticides {139,

273, 3 06, 316). Peach trees planted on these old apple-orchard sites usually

show symptoms of toxicity if the quantity of arsenic taken into the leaves

exceeds 2 parts per million of their dry weight (3 03). This extreme sensitivity of peach trees to arsenic has caused considerable loss to fruit growers

in the past, and much damage can still be found where careful control measures are not followed.

Fruit Species Affected

There is a marked difference in sensitivity of different kinds of fruit trees

to arsenic. Peach (Pnnim pérsica) and apricot (P. armcniaca) are most

easily injured; sweet cherry (P. avmm) is only moderately damaged; and

domestica plum (P. domestica), pear {Fyms communis), and apple {Malus

sylvestris) are very tolerant and show no symptoms whatsoever even though

planted on soils where the peach would be severely injured.

Symptoms

As a general rule arsenic-toxicity symptoms on peach do not become apparent until midsummer and appear first on the older or basal leaves. The

younger, terminal leaves frequently remain normal for a while or throughout

the season. The first indication of injury is the development of brown to

reddish-brown spots along the leaf margins. These spots also appear in the

leaf blade between the veins. Later these necrotic islands fall from the leaf,

leaving irregular-shaped holes—a shot-hole effect similar to that caused by

the western X-disease virus (pi. 27, £). In fact, the symptoms are so much

alike that arsenic injury has often been mistaken for western X-disease {139,

187). The injured tissue around the leaf margin may drop out, leaving a

ragged margin. In severely affected trees defoliation takes place later in the season, but any fruits on a tree remain attached and ripen somewhat prematurely

(pi. 27, F). The fruits do not attain full size and are astringent in flavor.

A similar injury results from arsenical sprays applied to peach trees. Peach

trees interplanted in apple orchards frequently show heavy defoliation resulting from arsenical-spray injury and the fruits cHng to the bare branches.

Control Measures

At the present time there appears to be no practical method of removing

arsenic from the soil; therefore, emphasis has been placed on the possibility

of reducing arsenic absorption by trees and of increasing the tolerance of

trees for arsenic. This has been accomplished by continued high-nitrogen

fertilization, together with occasional apphcations of zinc sulfate to the soil.

The addition of sulfur to either the high-nitrogen or the zinc-sulfate-highnitrogen treatment on alkaline soils slightly increased the effectiveness of these

treatments, but no difference was found when sulfur was added to acid soils

250
VIRUS DISEASES OF STONE FRUITS 251

(314). To establish the high nitrogen level for trees 3 years or older,

about 8 pounds of ammonium sulfate, or the equivalent nitrogen in other

carriers, is recommended. This should be used in spht applications—half in

December or January and half in May or June. The amount of zinc sulfate

is about 8 pounds per tree. This, as well as the nitrogen, should be broadcast

within a circle about 8 feet in diameter. One appUcation of zinc sulfate may

be effective for several years, but nitrogen should be applied annually. For

trees 1 or 2 years old, the quantities just given should be halved and applied

within a circle 4 feet in diameter.
LITERATURE CITED

VIRUS AND NONTRANSMISSIBLE VIRUSLIKE DISEASES

(1) ANDERSON, H. W., and SEIFERT, H. F.

1940. YELLOW-RED VIROSIS ON CHOPvECHERRY IN ILLINOIS. U. S. Buf. Plant InduS.,

Plant Dis. Rptr. 24: 340-341. [Processed.]

(2) ARNAUD, G., and ARNAUD, M.

1936. LES MALADIES À VIRUS DES ROSACEES AMYGDALEES. [Paris] Acad. dcS Sci.

Compt. Rend. 202: 869-871.

(3) ATANASOFF, D.

195 5. MOSAIC OF STONE FRUITS. Phytopath, Ztsclir. 8: [259]-284, illus.

(4) BAADE, J. H.

1928. DIAMOND CANKER IN NAPA COUNTY. Calif. Cult. 71: 494.

(5) BENNETT, C. W.

[1927.] PEACH YELLOWS AND LITTLE PEACH SITUATION IN MICHIGAN. Micll. State

Hort. Soc, Ann. Rpt, (1926) 56: 187-194.

(6) BERKELEY, G. H.

1941. THE "x" DISEASE ON PEACH AND cHOKEcHERRY. Canad. Hort. and Home

Mag., Growers' Ed., 64: 206, 220.

(7)

(8)

1941. PRUNE DWARF AND SHIRO LiNE=PATTERN MOSAIC. Canad. Hort. and Home

Mag., Growers' Ed., 64: 210, 211, 220, illus. (Reprinted as Pub, 679, Div.

Bot. and Plant Pathol., Sei. Serv., Dominion [Canada] Dept. Agr., [3] pp.,

illus. 1941.)

1947. CHERRY YELLOWS AND NECROTIC RING SPOT OF SOUR CHERRY IN ONTARIO. NO.

1. THE VALUE OF PRUNUS PÉRSICA AND P. DOMESTICA VAR. ITALIAN PRUNE

AS INDEX HOSTS. (Abstract) Phytopathology 37: 2-3.

(9) and WILLISON, R. S.

1948. YELLOWS AND NECROTIC RING SPOT OF SOUR CHERRIES IN ONTARIO: INOCULATION EXPERIMENTS. Phytopathology 38: J09-518, illus.

(10) BLAKE, M. A.

1910. PEACH YELLOWS AND LITTLE PEACH. N. J. Agr. Expt. Sta. Bul. 226, 26 pp.>

illus.

(11) COOK, M. T., and CONNORS, C. H.

1921. RECENT STUDIES ON PEACH YELLOWS AND LITTLE PEACH. N. J. Agr. Expt.

Sta. Bul. 3 56, 62 pp., illus.

(12) BLODGETT, E. C.

1937. FRUIT DISEASES IN IDAHO, 1936. U. S. Bur. Plant Indus., Plant Dis. Rptr. 21:

89-95. [Processed.]

(13)

(14)

(IS)

(16)

(17)

1939. SOME OBSCURE PEACH DISEASES IN IDAHO. U. S. Bur. Plant Indus., Plant Dis.

Rptr. 23: 216-218. [Processed.]

1939. INCIDENCE OF FRUIT DISEASES IN IDAHO IN 1937 AND 19 3 8. U. S. Bur. Plant

Indus., Plant Dis. Rptr, 23: 238-245. [Processed.]

1940. FRUIT DISEASES IN IDAHO, 1939. U. S. Bur. Plant Indus., Plant Dis. Rptr, 24:

177-182. [Processed.]

1940. A LEAF SPOT OF ITALIAN PRUNE PERPETUATED IN BUDDED STOCK. Phytopathology 30: 347-348, illus.

1941. FRUIT DISEASES IN IDAHO, 1940. U. S. Bur. Plant Indus., Plant Dis. Rptr. 25:

229-23 5. [Processed.]

252
VIRUS DISEASES OF STONE FRUITS 253

(18) BLODGETT, E. C.

1941. STUDIES ON PEACH viRosEs IN IDAHO. (Abstract) Phytopathology 31: 859-

860.

1942. FRUIT DISEASES IN IDAHO IN 1941. U, S. Bur. Plant Indus., Plant Dis. Rptr.

26: 10-15. [Processed.]

1943. FRUIT DISEASES IN IDAHO IN 1942. U. S. Bur. Plant Indus., Plant Dis. Rptr.

27: 82-86. [Processed.]

1943. PEACH WART. Phytopathology 33: 21-32, illu

1943. PRUNE DISEASES. Wash. State Hort. Assoc. Proc. 39: 59-64.

1943. RASP LEAF OF CHERRY. Phytopathology 33: 620-622.

1944. PEACH CALICO. Phytopathology 34: 65 0-657, illus.

(19)

(20)

(21)

(22)

(23)

(24)

(25)

(26)

(27) -

1947. SPARSE LEAF OF ITALIAN PRUNE. (Abstract) Phytopathology 37: 360.

(28) REEVES, E. L., WRIGHT, C. M., and WILLIAMS, H. E.

1948. THE OCCURRENCE AND TRANSMISSION OF LITTLE CHERRY IN WASHINGTON.

(Abstract) Phytopathology 3 8: 2-3.

(29) REEVES, E. L., WRIGHT, C. M., and others.

1947. THE LITTLE CHERRY DISEASE AND RELATED PROBLEMS IN WASHINGTON. Wash.

State Hort. Assoc. Proc. 43: [231]-240.

(3 0) BoDiNE, E. W.

1934. OCCURRENCE OF PEACH MOSAIC IN COLORADO. [U. S. Bur. Plant Indus.], Plant

Dis. Rptr. 18: 123. [Processed.]

(31)

(32)

1944. PLANT DISEASE SURVEYS IN IDAHO 1943-1944. U. S. Bur. Plant Indus., Soils,

and Agr. Engin., Plant Dis. Rptr. Sup. 149, pp. 400-407. [Processed.]

1946. TRANSMISSION OF PEACH WART BY GRAFT INOCULATIONS WITH AFFECTED

FRUIT TISSUE. Phytopathology 3 6: 675.

1936. PEACH MOSAIC DISEASE IN COLORADO. Colo. Expt. Sta. Bul. 421, 11 pp., illus.

(33)

(34)

1942. ANTAGONISM BETWEEN STRAINS OF THE PEACH-MOSAIC VIRUS IN WESTERN

COLORADO. (Abstract) Phytopathology 32: 1.

1942. FURTHER NOTES ON THE INCUBATION PERIOD OF THE PEACH MOSAIC VIRUS.

Science 9S: 2 56-2 57.

1944. VIRUS AND OTHER DISEASES OF STONE FRUITS IN WESTERN COLORADO. U. S.

Bur. Plant Indus., Soils, and Agr. Engin., Plant Dis. Rptr. 28: 780-781.

[Processed.]

(3 5) and DURRELL, L. W.

Î941. PEACH MOSAIC IN WESTERN COLORADO.. (Abstract) Phytopathology 31: 4.

(36) and DURRELL, L. W.

1941. HOST RANGE OF PEACH-MOSAIC VIRUS IN WESTERN COLORADO. Phytopathology

31: 322-3 3 3, illus.

(37) and DURRELL, L. W.

1941. VIRUS DISEASES OF PEACH IN WESTERN COLORADO. U. S. Bur. Plant Indus.,

Plant Dis. Rptr. 25: 474-475. [Processed.] (See paragraphs on "The

X-disease or yellow-red virosis," p. 474.)

(3 8) and KREUTZER, W. A.

1942. RING SPOT OF APRICOT. Phytopathology 32: 179-181, illus.

(39) and NEWTON, J. H.

1942. THE RASP LEAF OF CHERRY. Phytopathology 32: 3 3 3-3 3 5, illus.

(40) NEWTON, J, H., and KREUTZER, W. A.

1942. FOUR NEW VIRUS DISEASES OF STONE FRUITS FOUND IN PEACH MOSAIC STUDY IN

COLORADO. Colo. Farm. Bul. 4 (2): 6-10, illus.
254 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

(41) BoYD, O. C.

153 8. X-DISEASE OF PEACH FOUND IN MASSACHUSETTS. U. S. Bur. Plant InduS.,

Plant Dis. Rptr. 22: 3 34. [Processed.]

(42)

1939. DISTRIBUTION OF X-DISEASE OF PEACHES IN MASSACHUSETTS. U. S. Bur. Plant

Indus., Plant Dis. Rptr. 23: 341-342. [Processed.]

(43) CAESAR, L.

1910. LITTLE PEACH DISEASE. Ontario Dept. Agr., Bui. 185, 8 pp.

(44) CATION, D.

1932. THREE VIRUS DISEASES OF THE PEACH IN MICHIGAN. Mich. Agr. Expt, Sta,

Cir. Bui. 146, 11 pp., illus.

(40

{46)

(47)

(48)

(49)

(50)

(51)

193 3. AN INFECTIOUS ROSETTE OF PEACH TREES. Mich. Agr. Expt, Sta. Quart. Bui.

16: 79-84, illus.

1934. PEACH MOSAIC. Phytopathology 24: 13 80-13 8!.

1941. THE LINE PATTERN VIROSIS OF THE GENUS PRUNUS, Phytopathology 31: 1004-

1010, illus.

1941. *'X" DISEASE OF PEACH AND CHOKE-CHERRY FOUND IN MICHIGAN. U. S. Bur.

Plant Indus., Plant Dis. Rptr. 25: 406-407. [Processed.]

1942. NECROTIC SPOT, A PEACH DISEASE TRANSMISSIBLE BY BUDDING. (Abstract)

Phytopathology 32: 2.

1942. THE ROSETTE MOSAIC DISEASE OF PEACH. Mich. Agr. Expt. Sta, Tcch. Bui.

18 0, 24 pp., illus.

1949. TRANSMISSION OF CHERRY YELLOWS VIRUS COMPLEX THROUGH SEEDS. Phytopathology 39: 37-40, illus.

(52) CAVANAGH, A. E.

1937. REPORT ON PHONY PEACH DISEASE CONTROL, TENNESSEE. Tenn. State Hort.

Soc. Proc. 32: 48-53.

(53) CHRISTOFF, A.

193 8. VIRUS DISEASES OF THE GENUS PRUNUS IN BULGARIA. Phytopath. Ztschr. 11:

[360]-422, illus.

(54) CLAYTON, C. N.

1946. SOUR CHERRY YELLOWS IN NORTH CAROLINA. U. S. Bur. Plant Indus., Soils,

and Agr. Engin., Plant Dis. Rptr. 30: 246. [Processed.]

(55)

1949. ASTEROID SPOT OF PEACH IN NORTH CAROLINA. Phytopathology 39: S99-

600, illus.

(56) COCHRAN, L. C.

1942. SHOCK EFFECT OF CERTAIN VIRUSES OF TEIE MOSAIC GROUP ON PEACH. (Abstract) Phytopathology 32: 827.

(57)

(58)

(59)

(59a)

1944. THE "COMPLEX CONCEPT" OF THE PEACH MOSAIC AND CERTAIN OTHER STONE

FRUIT VIRUSES. (Abstract) Phytopathology 34: 934.

1946, PASSAGE OF THE RING SPOT VIRUS THROUGH MAZ2ARD CHERRY SEEDS. ScÎenCÊ

104: 269-270.

1946. RING SPOT, A COMMON CONTAMINANT OF STONE FRUIT-VIRUS CULTURES. (Abstract) Phytopathology 36: 396.

19 50. PASSAGE OF THE RING-SPOT VIRUS THROUGH PEACH SEEDS. (Abstract) Phytopathology 40: 964.

(60) and HuTcHiNs, L. M.

1937. PEACH-MOSAIC HOST-RELATIONSHIP STUDIES IN SOUTHERN CALIFORNIA. (Abstract) Phytopathology 27: 9 54.
VIRUS DISEASES OF STONE FRUITS 255

(61) CocHRAN, L. C, and HUTCHINS, L. M.

li?3 8. FURTHER STUDIES ON HOST RELATIONSHIPS OF PEACH MOSAIC IN SOUTHERN

CALIFORNIA. Phytopathology 28: 890-892, illus.

(62) and HUTCHINS, L. M.

1941. A SEVERE RING-SPOT VIROSIS ON PEACH. (Abstract) Phytopathology 31: 860.

(63) and RUE, J. L.

1944. SOME HOST-TISSUE RELATIONSHIPS OF THE PEACH MOSAIC VIRUS. (Abstract)

Phytopathology 34: 934.

(64) and RUE, J. L.

1946. INTERACTION OF SOME FORMS OF THE PEACH-MOSAIC VIRUS. (Abstract)

Phytopathology 36: 396.

(65) and SMITH, C. O.

193 8. ASTEROID SPOT, A NEW VIROSIS OF THE PEACH, Phytopathology 28: 278-281,

illus.

(66) CoE, D, M.

1943. REPORT OF THE 1942 STONE FRUIT VIRUS DISEASE SURVEY OF WASHINGTON.

Wash. State Dept. Agr. Bui. 2, 19 pp., illus.

(67) CoRDY, C. B.

1942. OBSERVATIONS OF BUCKSKIN DISEASE OF CHERRY. Oreg. State Hort. Soc. Ann.

Rpt. 34: [91]-92.

(68) CROSBY, C. R-, MILLS, W. D., and BLAUVELT, W. E.

1929. PROTECTING ORCHARD CROPS FROM DISEASES AND INSECTS. N. Y. (Cornell)

Agr. Expt. Sta. Bui. 498, 80 pp., illus.

(69) EASTHAM, J. W.

1941. REPORT OF PROVINCIAL PLANT PATHOLOGIST. Brit. Columbia Dept. Agr.,

Ann. Rpt. (1940) 35: 49-56.

(70)

1941. REPORT OF PROVINCIAL PLANT PATHOLOGIST. Brit. Columbia Dept. Agr., Ann.

Rpt. 36: 46-51.

(71) FAWCETT, H. S.

1940. SUGGESTIONS ON PLANT VIRUS NOMENCLATURE AS EXEMPLIFIED BY NAMES FOR

CITRUS VIRUSES. Science 92: 5 59—561.

(72) and BITANCOURT, A. A.

1943. COMPARATIVE SYMPTOMATOLOGY OF PSOROSIS VARIETIES ON CITRUS IN CALIFORNIA. Phytopathology 33: 837-864, illus.

(73) FOSTER, W. R., and LOTT, T. B.

1947. "LITTLE CHERRY," A VIRUS DISEASE. Sci. Agr. 27: 1-6, illus.

(74) GADDIS, B. M.

1936. ERADICATION OF CITRUS CANKER AND CONTROL OF PHONY PEACH AND PEACH

MOSAIC, PROGRESS REPORT, Jour. Econ. Ent. 29: 940-944.

(75)

1937. CONTROL OF PHONY PEACH DISEASE. In U. S. Bur. Plant Indus., Plant Dis.

Rptr. Sup. 99, Some Aspects of the Plant Disease Eradication and Control

Work of the Bureau of Entomology and Plant Quarantine, pp. 36-41.

[Processed.]

(76) GLOYER, "W. O., and GLASGOW, H.

1928. DEFOLIATION OF CHERRY TREES IN RELATION TO WINTER INJURY. N. Y. State

Agr. Expt. Sta. Bui. 5 5 5, 27 pp., illus.

(77) GROVES, A. B.

1941. ACTIVE SPREAD OF PEACH YELLOWS IN NORTHERN VIRGINIA. U. S. Bur. Plant

Indus., Plant Dis. Rptr. 25: 408-409. [Processed.]

(78) HARRIS, M. R.

1944. x-DisEASE ON PEACH IN NORTHERN OHIO. U. S. Bur. Plant Indus., Soils, and

Agr. Engin., Plant Dis. Rptr. 28: 840. [Processed.]

(79) HARTZELL, A.

1935. A STUDY OF PEACH YELLOWS AND ITS INSECT VECTOR. Boyce Thompson Inst.

Contrib. 7: 183-207, illus.

(80)

1936. INCUBATION PERIOD OF PEACH YELLOWS IN ITS INSECT VECTOR. Boyce Thompson Inst. Contrib. 8: 113-120, illus.

(81) [HEALD, F. D., JONES, L. K., and HUBER, G. A.]

1934. PLANT DISEASE SURVEY. Wash. Agr. Expt. Sta. Ann. Rpt. (Bui. 305) 44:

50-51.
256 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

(82) HILDEBRAND, E. M.

1941. A NEW CASE OF ROSETTE MOSAIC ON PEACH. Phytopathology 31: 353-355, illus.

(83)

(84)

(85)

(U)

(87)

(88)

(89)

(90)

(91)

(92)

(93)

(94)

(95)

1941. RAPID TRANSMISSION OF YELLOW-RED VIROSIS IN PEACH. Boyce Thompson

Inst. Contrib. 11: 485-496, illus.

1942. INDEXING CHERRY YELLOWS ON PEACH. Phytopathology 32: 712-719, illus.

1942. PRUNE DWARF. Phytopathology 32: 741-751, illus.

1942. RAPID TRANSMISSION TECHNIQUES FOR STONE-FRUIT VIRUSES, Science 95\ 52.

1942. TRADE ROLL IN CONTROL OF CHERRY YELLOWS. Amer. Nurscryman 75 (8):

9-10,

1943. STRAINS OF YELLOWS VIRUS IN MONTMORENCY CHERRY. (Abstract) Phytopathology 3 3:6.

1944. VIRUS SYMPTOMS ON MONTMORENCY CHERRY IN A BAD FUNGUS LEAF SPOT

YEAR. U. S. Bur. Plant Indus., Soils, and Agr. Engin., Plant Dis. Rptr. 28:

993-994. [Processed.]

1944. CAN THE ADVERSE EFFECTS OF VIRUS DISEASES BE CORRECTED BY EXTRA FERTILIZATION AND PRUNING THE MONTMORENCY CHERRY? U. S. Bur. Plant

Indus., Soils, and Agr. Engin., Pknt Dis. Rptr. 28: 10 57-1060. [Processed.]

1944. THE CHERRY VIRUS COMPLEX IN NEW YORK. (Abstract) Phytopathology 34:

1003.

1944. PRUNE DWARF AND TPÍE CHERRY VIRUS COMPLEX. ScicnCC 100: 147-148.

1945. THE DODDER VECTOR OF WOODY PLANT VIRUSES. U. S. Bur. Plant Indus., Soils,

and Agr. Engin., Plant Dis. Rptr. 29: 196-197. [Processed.]

1945. MYROBALAN MOTTLE AND ASTEROID SPOT. Phytopathology 35: 47-50, illus.

1945. VIRUSES AND CHERRY ROOTSTocKs. Amer. Nurseryman 82 (7): 5-8, 18-21,

illus,

(96) BERKELEY, G. H., and CATION, D., compilers.

1942. HANDBOOK OF VIRUS DISEASES OF STONE FRUITS IN NORTH AMERICA. Mich.

Agr. Expt. Sra. Misc. Pub. [LTnnumb.], 76 pp.

(97) — and CURTIS, O. F.

1942. A DARKENING TECHNIQUE FOR INDUCING VIRUS SYMPTOMS IN MATURE AS WELL

AS IN GROWING LEAVES. Science 95: 390,

(98) and MILLS, W. D.

1941. CHERRY YELLOWS (PHYSIOLOGICAL YELLOW LEAF ) IN NEW YORK. Phytopathology 31: 3 5 5-3 56.

(99) — and PALMITER, D. H.

193 8. x-viRUs DISEASE ON PEACHES IN NEW YORK, U. S. Bur. Plant Indus., Plant

Dis. Rptr. 22: 268. [Processed.]

(100) and PALMITER, D. H.

1938. YELLOW-RED VIROSIS (X-DISEASE) OF PEACH AND CHOKECHERRY. U. S. Bur,

Plant Indus., Plant Dis. Rptr. 22: 3 94-396, illus. [Processed.]

(101) and PALMITER, D. H.

1940. STATUS OF YELLOW-RED VIROSIS IN 1940. U. S. Bur. Plant Indus., Plant Dis.

Rptr. 24: 470-473, illus. [Processed.]

(102) and PALMITER, D. H.

1940. YELLOW-RED OR "X" DISEASE: A NEW THREAT TO PEACH INDUSTRY. (Abstract)

Phytopathology 3 0: 10.

(103) — and PALMITER, D. H.

1942. HOW TO PREVENT DESTRUCTION OF NEW YORK STATE PEACH ORCHARDS BY

THE NEW YELLOW-RED VIRUS DISEASE. N. Y. State Hort, Soc. Proc. 87:

34-40.
VIRUS DISEASES OF STONE FRUITS 257

(104) HOLMES, F. O.

1941. HANDBOOK OF PHYTOPATHOGENTC VIRUSES. 221 pp. Minneapolis, Minn.

[Processed.]

(105)

1948. THE FILTERABLE VIRUSES. Reprint of Supplement No. 2, Bergey's Manual of

Determinative Bacteriology, Ed. 6 (1948), pp. 1127-1286, with revised

and enlarged index. Baltimore, Md.

(106) HOUSTON, B. R., ESAU, IC, and HEWITT, W. B.

1947. THE MODE OF VECTOR FEEDING AND THE TISSUES INVOLVED IN THE TRANSMISSION OF PIERCE'S DISEASE VIRUS IN GRAPE AND ALFALFA. Phytopathology 37: 247-25 3, illus.

(107) HUTCHINS, L. M.

192 8. PEACH ORCHARDS IN GEORGIA MENACED BY PHONY DISEASE. U. S. Dept.

Agr. Yearbook of Agr. 1927: 499-503, illus.

(108)

(109)

(110)

(111)

(112)

(113)

1929. PHONY DISEASE OF THE PEACH. (Abstract) Phytopathology 19: 107.

193 0. UNE MALADIE À VIRUS DU PECHER (pHONY PEACH). Rev. de Path. Vég. et

d'Ent. Agr. de France 17: [3 83]-384, illus.

1930. THE PHONY DISEASE OF THE PEACH. Jour. Econ. Ent. 23: 5 5 5-562, illus.

1932. PEACH MOSAIC—A NEW VIRUS DISEASE. Science 76\ 123.

193 3. IDENTIFICATION AND CONTROL OF THE PHONY DISEASE OF THE PEACH.

Ga. Off. State Ent. Bui. 78, 5 5 pp., illus. [Partial translation into Italian

by A. Ott: Note di Fruttic. (R. Osserv. di Fruttic, Pistoia) 12: 44-53,

61-70, 77-83, illus. 1934.]

1939. APPARENT LOCALIZATION OF PHONY DISEASE VIRUS IN THE WOODY CYLINDER.

(Abstract) Phytopathology 29: 12.

(114) — BoDiNE, E. W., and THORNBERRY, H. H.

1937. PEACH MOSAIC, ITS IDENTIFICATION AND CONTROL. U. S. Dept. Agr. Cir.

427, 48 pp., illus.

(115) ——— and COCHRAN, L. C.

1940. PEACH-MOSAIC VIRUS STRAIN STUDIES. (Abstract) Phytopathology 30: 11.

(116) and RUE, J. L.

1939. PROMISING RESULTS OF HEAT TREATMENTS FOR INACTIVATION OF PHONY

DISEASE VIRUS IN DORMANT PEACH NURSERY TREES. (Abstract) Phytopathology 29: 12.

(117) — and RUE, J. L.

1949. NATURAL SPREAD OF PHONY DISEASE TO APRICOT AND PLUM. Phytopathology

39: 661-G67, illus.

(118) IDAHO AGRICULTURAL EXPERIMENT STATION.

1948. LITTLE CHERRY DISEASE THREATENS IDAHO CHERRY ORCHARDS. Idaho Agr.

Expt. Sta. Cir. 113, [4] pp., illus.

(119)

1949. WESTERN X DISEASE OF PEACHES IN IDAHO. Idaho Agr. Expt. Sta. Cir. 115,

[4] pp., illus,

(120) JOHNSON, J.

1949. SYSTEMS OF VIRUS CLASSIFICATION AND NOMENCLATURE. Tljdschr. OVer i lantenziekten 55: 128-137. [In English. Dutch summary, p. 13 5.]

(121) KEITT, G. W., and CLAYTON, C. N.

1939. A DESTRUCTIVE BUD-TRANSMISSIBLE DISEASE OF SOUR CHERRY IN WISCONSIN.

Phytopathology 29: 821-822.

(122) — and CLAYTON, C. N.

1940. A BUD-TRANSMISSIBLE CHLOROSIS OF PRUNUS CERASUS. (Abstract) Phytopathology 30: 13.

(123) and CLAYTON, C. N.

1941. FURTHER EXPERIMENTS ON A VIRUS DISEASE OF PRUNUS CERASUS. (Abstract)

Phytopathology 31: 14.

891793 0—51—20
258 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

(124) KEITT, G. W., and CLAYTON, C. N.

1943. A DESTRUCTIVE VIRUS DISEASE OF SOUR CHERRY, Phytopathology 331 449-

468, iUus.

(12 5) and MOORE, J. D.

1943. MASKING OF LEAF SYMPTOMS OF SOUR-CHERRY YELLOWS BY TEMPERATURE

EFFECTS. Phytopathology 33: 1213-1215.

(126) KIENHOLZ, J. R.

1947. PINTO LEAF, A TRANSMISSIBLE DISEASE OF CHERRY. Phytopathology 37:

64-66, illus.

(127) KiNMAN, C. F.

193 0. A STUDY OF SOME UNPRODUCTIVE CHERRY TREES IN CALIFORNIA. Jour. Agr.

Res. 41: 327-3 3 5, illus.

(128) KUNKEL, L. O.

1930. INCUBATION PERIOD OF PEACH YELLOWS AS AFFECTED BY POINT OF INOCULATION. Science 71: 516.

(129)

(130)

(131)

(132)

(133)

(134)

(135)

(136)

193 3. INSECT TRANSMISSION OF PEACH YELLOWS. Boyce Thompson Inst. Contrib.

5: 19-28, illus.

193 6. IMMUNOLOGICAL STUDIES ON THE THREE PEACH DISEASES, YELLOWS, ROSETTE,

AND LITTLE PEACH. Phytopathology 26: 201-219, illus.

1936. HEAT TREATMENTS FOR THE CURE OF YELLOWS AND OTHER VIRUS DISEASES

OF PEACH. Phytopathology 26: 809-83 0, illus.

193 6. PEACH MOSAIC NOT CURED BY HEAT TREATMENTS. Amer. Jour. Bot, 23:

683-686, illus.

193 8. CONTACT PERIODS IN GRAFT TRANSMISSION OF PEACH VIRUSES, Phytopathology

28: 491-497, illus.

193 8. INSECTS IN RELATION TO DISEASES OF FRUIT TREES AND SMALL FRUITS, Jour.

Econ. Ent. 31: 20-22.

1943. NEW HOSTS AS A KEY TO PROGRESS IN PLANT VIRUS DISEASE RESEARCH. In

Rockefeller Institute for Medical Research, Virus Diseases, pp. [6l]-82,

illus. Irhaca, N. Y.

1944. TRANSMISSION OF VIRUS FROM X-DISEASED PEACH TREES TO HERBACEOUS

PLANTS. (Abstract) Phytopathology 34: 1006.

(137) LEWIS, F. H.

1946. RINGSPOT AND YELLOWS OF SOUR CHERRY IN PENNSYLVANIA. N, Y. STATE

Hort. Soc. Proc. 91: 17-20.

(138)

1947. NOTES ON TWO VIRUS DISEASES OF SOUR CHERRIES. Pa. State Hort. Assoc.

Proc. 88: 65-71.

(139) LINDNER, R. C, and REEVES, E. L.

1942. ARSENIC INJURY OF PEACH TREES: A DISORDER SOMETIMES CONFUSED WITH

WESTERN x-DisEASE. \Yash. State Hort. Assoc. Proc. 38: 3 7-40, illus.

(140) LoTT, T. B.

1943. TRANSMISSIBLE ^TWISTED LEAF" OF SWEET CHERRY. Sci. Agr. 23: 439-441,

illus.

(141)

1945. "l>AMBERT MOTTLE," A TRANSMISSIBLE DISEASE OF SWEET CHERR.Y. Sci. Agr.

25: 776-779, illus,

(142)

1947. "SMALL BITTER CHERRY," A FRUIT ABNORMALITY OF THE BING CHERRY

VARIETY. Sci. Agr. 27: 260-262, illus.

(142a) =

19 50. SOME FURTHER OBSERVATIONS ON SMALL BITTER CHERRY. Sci. Agr. 3 0: 444-

446, illus.

(143) MCCLïNTOCK, J. A.

1923. PEACH ROSETTE, AN INFECTIOUS MOSAIC. Jour. Agr. Res. 24: 307-316, illus.
VIRUS DISEASES OF STONE FRUITS 259

144). MCCLINTOCK, J. A.

1931. CROSS-INOCULATION EXPERIMENTS WITH ERIGERON YELLOWS AND PEACH

ROSETTE. Phytopathology 21: 373-3 86, illus.

145) McKiNNEY, H. H.

1944. GENERA OF THE PLANT VIRUSES. Wash, Acad. Sei. Jour. 34: 139-154.

146) MCLARTY, H. R.

193 5. CHERRY MOTTLE LEAF. Northwest Assoc. Hort., Ent., and Plant Path.

(H. E. P. P.), Abs. of Papers 1: 5. [Processed.]

147) MANNS, T. F.

1934. THE DISSEMINATION OF YELLOWS AND LITTLE PEACH. Del. Agr. Expt. Sta.

(Ann. Rpt. 1932-33) Bui. 188, pp. 36-38.

[1934.] OUR PRESENT KNOWLEDGE ON THE DISSEMINATION OF YELLOWS AND LITTLE

PEACH. Peninsula Hort. Soc. [Del.] Trans. (193 3) 47: 17-19.

1936. PEACH YELLOWS AND LITTLE PEACH STUDIES. (Abstract) Phytopathology

26: 101.

148)

149)

150)

1942. PEACH YELLOWS AND LITTLE PEACH. Del. Agr. Expt. Sta. Bui. 236, 50 pp.,

illus.

151) and DAVIES, F. R.

1936. DISSEMINATION OF PEACH YELLOWS AND LITTLE PEACH BY MACROPSIS TRIMACULATA, FITCH. Del. Agr. Expt. Sta. (Ann. Rpt. 193 5-36) Bui. 205,

pp. 37-3 8.

152) and MANNS, M. M.

293 5. THE DISSEMINATION OF PEACH YELLOWS AND LITTLE PEACH. Del. Agr. Expt.

Sta. (Ann. Rpt. 193 3-34) Bui. 192, pp. 40-44, illus.

153) and MANNS, M. M.

[1935.] PLUMS AS FACTORS IN THE DISSEMINATION OF YELLOWS AND LITTLE PEACH.

Peninsula Hort. Soc. [Del.] Trans. (1934) 48: 72-76, illus.

154) MiLBRATH, J. A.

1947. VIRUS DISEASES OF STONE FRUITS. Oreg. State Hort. Soc. Ann. Rpt. 39:

43-45.

155) — and ZELLER, S. M.

1942. ROUGH-BARK, A VIRUS DISEASE OF FLOWERING CHERRY. Phytopathology 32:

428-430, illus.

156) and ZELLER, S. M.

1945. LATENT VIRUSES IN STONE FRUITS. Science 101: 114-115.

157) and ZELLER, S. M.

1948. INDEXING FRUIT TREES FOR VIRUS. Amer. Nurseryman 88 (5): 7-8, illus.

158) MILLER, H. J.

1941. YELLOW-RED VIROSIS IN PENNSYLVANIA. U. S. Bur. Plant Indus., Plant Dis.

Rptr. 25: 419. [Processed.]

159) MILLS, W. D.

1946. TEMPERATURE EFFECTS ON THE EXPRESSION OF THE YELLOWS VIRUS IN SOUR

CHERRIES. Phytopathology 36: 3 5 3-3 58,

160) MooRE, J. D.

1946. RELATION OF SOUR CHERRY YELLOWS TO YIELD. (Abstract) Phytopathology

36: 406.

161)

1947. HEAT TREATMENTS OF SOUR CHERRY CARRYING YELLOWS AND NECROTIC RING

SPOT. (Abstract) Phytopathology 37: 16.

162) BOYLE, J. S., and KEITT, G. W.

1948. MECHANICAL TRANSMISSION OF A VIRUS DISEASE TO CUCUMBER FROM SOUR

CHERRY. Science 108: 623-624.

163) and KEITT, G. W.

1944. HOST RANGE STUDIES OF NECROTIC RING SPOT AND YELLOWS OF SOUR CHERRY.

(Abstract) Phytopathology 34: 1009.

164) and KEITT, G. W.

1946. RELATION OF TEMPERATURE TO EXPRESSION OF SYMPTOMS OF SOUR CHERRY

YELLOWS AND NECROTIC RING SPOT, (Abstract) Phytopathology 36: 406-

407.

891793 0—51—21
260 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

(165) MOORE, J. D., and KEITT, G. W.

1947. TEMPERATURE AND SEASONAL DEVELOPMENT OF HOST IN RELATION TO

EXPRESSION OF LEAF SYMPTOMS OF SOUR CHERRY YELLOWS. (Abstract)

Phytopathology 37: 16,

(166) and KEITT, G. W.

1949. AN INDEXING METHOD FOR NECROTIC RING SPOT AND YELLOWS OF SOUR

CHERRY. (Abstract) Phytopathology 39: 15-16.

(167) NEAL, D. C.

1920. PHONY PEACHES: A DISEASE OCCURRING IN MIDDLE GEORGIA. Phytopathology

10: [l06]-ril0], illus.

(168) NICHOLS, C. W.

1948. THE LITTLE CHERRY SITUATION IN IDAHO. U. S. Bur. Plant Indus., Soils, and

Agr. Engin., Plant Dis. Rptr. 32: 433-434. [Processed.]

(169) PALMITER, D. H., and HILDEBRAND, E. M.

1940. PROTECTING PEACH ORCHARDS FROM YELLOW-RED VIRUSES (X-DISEASE).

N. Y. State Hort. Soc. Proc. 85: 183-187.

(170) and HILDEBRAND, E. M.

1943. THE YELLOW-RED VIROSIS OF PEACH: ITS IDENTIFICATION AND CONTROL.

N. Y. State Agr. Expt. Sta. Bui. 704, 17 pp., illus.

(171) and PARKER, K. G.

1948. PEACH X-DISEASE ON SOUR CHERRY. (Abstract) Phytopathology 38: 20.

(172) — and PARKER, K. G.

1949. PEACH "X-DISEASE" NOW THREATENS SOUR CHERRIES. Farm Res. [N. Y. State

and Cornell Agr. Expt. Stas.] 15 (1): [12]-[13], illus.

(173) PARKER, K. G., and PALMITER, D. H.

1948. x-DisEASE ON SOUR CHERRY IN NEW YORK. U. S. Bur. Plant Indus., Soils,

and Agr. Engin., Plant Dis. Rptr. 32: 188-190. [Processed.]

(174) PETERS, R.

18 08. ON PEACH TREES. Phila. Soc. Prom. Agr. Mem. 1: 15-24. (Read Feb. 11,

1806; with postscripts.)

(175) RASMUSSEN, E. J.

193 8. CAUSES OF PREMATURE DEFOLIATION OF SOUR CHERRY. Greg. State Hort.

Soc. Ann. Rpt. 30: 131-137.

(176) and CATION, D.

1942. EXPERIMENTS ON THE YELLOWS DISEASE OF SOUR CHERRY (PRUNUS CERASUS).

(Abstract) Phytopathology 32: 15.

(177) — and CATION, D.

1942. A PROGRESS REPORT ON THE YELLOW-LEAF DISEASE OF SOUR CHERRY. Mich.

State Hort. Soc. Ann. Rpt. (1941) 71: 100-105.

(178) RAWLINS, T. E., and HORNE, W. T.

1931. "BUCKSKIN," A DESTRUCTIVE GRAFT-INFECTIOUS DISEASE OF THE CHERRY.

Phytopathology 21: 3 31-33 5, illus.

(179) and PARKER, K. G.

1934. INFLUENCE OF ROOTSTOCKS ON THE SUSCEPTIBILITY OF SWEET CHERRY TO

THE BUCKSKIN DISEASE. Phytopathology 24: 1029-1031.

(180) and THOMAS, H. E.

1941. THE BUCKSKIN DISEASE OF CHERRY AND OTHER STONE FRUITS. Phytopathology

31: 916-92 5, illus.

(181) REEVES, E. L.

193 5. MOTTLE LEAF OF CHERRIES. Wash. State Hort. Assoc. Proc. 31: 8 5-89, illus.

(182)

1940. RUSTY-MOTTLE, A NEW VIROSIS OF CHERRY. (Abstract) Phytopathology 30:

789.

(183)

1941, MOTTLE LEAF, A VIRUS DISEASE OF CHERRIES. Jour. Agr. Rcs. 62: 555-572,

illus.

(184)

1943. VIRUS DISEASES OF FRUIT TREES IN WASHINGTON. Wash. State Dept. Agr.

Bui. 1, 25 pp., illus.

(185) BLODGETT, E. C, and FISCHER, G. W.

1946. THE PROBLEM OF LITTLE CHERRY DISEASE IN WASHINGTON. "Wash. State

Hort. Assoc. Proc. 42: 115-118,
VIRUS DISEASES OF STONE FRUITS 261

(186). REEVES, E. L., HUBER, G. A., and BAUER, K. E.

1939. "PINK-FRUIT" OR NECROSIS OF SOUR CHERRY IN WESTERN WASHINGTON.

U. S. Bur. Plant Indus., Plant Dis. Rptr. 23: 10-12. [Processed.]

(187) and HUTCHINS, L. M.

1940. OBSERVATIONS ON THE NEW SO-CALLED VIRUS DISEASE OF PEACH TREES IN

WASHINGTON, Wash. State Hort. Assoc. Proc. 3 6: 116-119.

(188) and HUTCHINS, L. M.

1941. A PROGRESS REPORT ON WESTERN X-DISEASE, A VIRUS DISEASE OF PEACHES.

Wash. State Hort. Assoc. Proc. 37: 27-30.

(189) and RICHARDS, B. L.

1946. A RUSTY MOTTLE-LIKE VIRUS DISEASE OF THE SWEET CHERRY ÏN UTAH.

(Abstract) Phytopathology 36: 409.

(190) RHOADS, A. S.

1945. VIRUS AND VIRUS-LIKE DISEASES OF SWEET CHERRY IN UTAH, AND NOTES ON

SOME CONDITIONS AFFECTING VARIOUS FRUIT CROPS. U. S. Bur. Plant Indus.,

Soils, and Agr. Engin., Plant Dis. Rptr. 29: 6-19. [Processed.]

(191) _

194Í. SURVEYS FOR WESTERN X-DISEASE IN UTAH PEACH ORCHARDS. U. S. Bur.

Plant Indus., Soils, and Agr. Engin., Plant Dis. Rptr. 29: 114-116.

[Processed.]

(192) RICHARDS, B. L.

1936. REPORT OF A SURVEY OF FIELD CONDITIONS IN THE REGION OF NORTHPORT,

WASHINGTON, GROWING SEASON 193 J. [Canada] Trail Smelter Ques. Docs.,

Ser. D, App. D6, 41 pp., illus.

(193)

1937. REPORT OF A SURVEY OF FIELD CONDITIONS IN THE REGION OF NORTHPORT,

WASHINGTON, GROWING SEASON 193 6. [Canada] Trail Smelter Ques. Docs.,

Ser. DD (pt. 2), App. DD4, 83 pp., illus.

1940. VIRUS DISEASE OF PEACHES SPREADING IN UTAH. Farm & Home Sei. [Utah

Agr. Expt. Sta.] 1 (4): [l], 11, illus. (Reprinted in part in U. S. Bur.

Plant Indus., Plant Dis. Rptr. 24: 474. 1940. [Processed.]

1945. RUSTY MOTTLE OF THE SWEET CHERRY IN UTAH. (Abstract) Utah Acad.

Sei., Arts and Letters Proc. (1944-45) 22: 8-9.

(194)

(195)

(196)

1945. THE RED-LEAF CHOKECHERRY VIRirS AS A POSSIBLE CAUSE OF WILT IN THE

SWEET CHERRY AND OF DIEBACK IN THE SOUR CHERRY. (Abstract) Utah

Acad. Sei., Arts and Letters Proc. (1944-45) 22: 9.

(197) — and HUTCHINS, L. M.

1941. A NEW VIROSIS OF PEACH IN UTAH, RESEMBLING X-DISEASE (YELLOW-RED

VIROSIS). (Abstract) Phytopathology 31: 19.

(198) HUTCHINS, L. M., and REEVES, E. L.

1949. THE WESTERN "X" VIRUS A CAUSE OF "LITTLE CHERRY" IN UTAH. (Abstract)

Phytopathology 39: 19.

(199) REEVES, E. L., and HUTCHINS, L. M.

1946. WILT AND DECLINE, A VIRUS DISEASE OF SWEET AND SOUR CHERRIES IN UTAH.

(Abstract) Phytopathology 36: 409.

(200) and RHOADS, A. S.

1945. RUSTY MOTTLE OF THE SWEET CHERRY IN UTAH. Farm & Home Sei. [Utah

Agr. Expt. Sta.] 6 (3): 6-8, 11, illus.

(200a) and WADLEY, B. N.

1950. STATUS OF OUR KNOWLEDGE OF THE WESTERN-X VIRUS IN UTAH. (Abstract)

Phytopathology 40: 969.

(201) WADLEY, B. N., and COCHRAN, G. W.

1948. LITTLE CHERRY, A VIRUS DISEASE OF SWEET AND SOUR CHERRIES IN UTAH.

Farm & Home Sei. [Utah Agr. Expt. Sta.] 9 (4): 10-12, illus.

(202) SCHNEIDER, H.

1945. ANATOMY OF BUCKSKIN-DISEASED PEACH AND CHERRY. Phytopathology 3 5:

610-63 5, illus.

(203) SEIFERT, H. F., and ANDERSON, H. W.

1939. YELLOW-RED VIROSIS ON CHOKECHERRY IN ILLINOIS. U. S. Bur. Plant Indus.,

Plant Dis. Rptr, 23 r 328. [Processed.]
262 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

(204) SiMONDS, A. O.

1949. APRICOTS AND PLUMS AS HOSTS OF WESTERN X-DISEASE. Science 109: 199.

(20o SMITH, C. C, and COCHRAN, L. C.

1943. A NONINFECTIOUS HERITABLE LEAF-SPOT AND SHOT-HOLE DISEASE OF THE

BEATY PLUM. Phytopathology 3 3: 1101-1103, illus.

(206) SMITH, E. F.

1888. PEACH YELLOWS: A PRELIMINARY REPORT. U. S. Dept. Agr. Bot. Div. Bui.

9, 254 pp., illus.

(207)

(208)

(209)

(210)

1891. ADDITIONAL EVIDENCE ON THE COMMUNICABILITY OF PEACH YELLO>5?S AND

PEACH ROSETTE. U. S. Dept. Agr. Div. Veg. Path. Bui. 1, 65 pp., illus.

1891. THE PEACH ROSETTE. Jour. Mycol. 6: 143-148, illus.

1893. ADDITIONAL NOTES ON PEACH KosETTE. Jour, Mycol. 7: 226-232.

1894. PEACH YELLOWS AND PEACH ROSETTE. U. S. Dept. Agr. Farmers' Bui. 17,

20 pp., illus.

(211) SMITH, K. M.

1937. A TEXTBOOK OF PLANT VIRUS DISEASES. 615 pp., illus. London.

(212) SMITH, R. E.

1932. THE DIAMOND CANKER DISEASE OF THE FRENCH PRUNE IN CALIFORNIA.

Calif. Agr. Col. Ext. Cir. 67, 22 pp., illus.

(213)

1941. DISEASES OF FRUITS AND NUTS. Calif. Agr. Col. Ext. Cir. 120, 168 pp., illus.

(214)

1941. TRANSMISSION OF DIAMOND CANKER OF THE FRENCH PRUNE. Phytopathology

31: 8 86-895, illus.

(215) STEWART, F. C.

1919. NOTES ON NEW YORK PLANT DISEASES, XL N. Y. [State] Agr, Expt. Sta. Bui.

463, pp. 157-18 8, illus.

(216) STODDARD, E. M.

1934. PROGRESS REPORT OF INVESTIGATIONS ON A NEW PEACH TROUBLE, Conn.

Pomol. Soc. Proc. (193 3) 43: 115-117.

(217)

(218)

(219)

(220)

(221)

(222)

(223)

(224)

(225)

19 3 5. PROGRESS REPORT ON THE INVESTIGATION OF A NEW PEACH DISEASE. Conn.

Pomol. Soc. Proc. (1934) 44: 31-3 6.

1936. PROGRESS REPORT OF THE "x" DISEASE OF PEACH. Conn, Pomol. SoC. ProC.

(1935) 45: 25-27.

1937. PROGRESS REPORT ON INVESTIGATIONS OF THE "x" DISEASE OF THE PEACH.

Conn. Pomol. Soc. Proc. (1936) 46: 15-18.

193 8. THE PRESENT STATUS AND SOME OBSERVATIONS ON THE "x'* DISEASE OF THE

PEACH IN CONNECTICUT. Conn. Pomol. Soc. Proc. (1937) 47: 95-97.

193 8. THE "x DISEASE" OF PEACH. Conn. (State) Agr. Expt. Sta. Cir. 122, pp.

[551-60, illus.

1939. NOTES ON "X-DISEASE" OF PEACH CONTROL IN CONNECTICUT AND REPORT

FROM WISCONSIN. U. S. Bur. Plant Indus., Plant Dis. Rptr. 23: 3 86.

[Processed.]

1941. A NEW HOST FOR THE X-DISEASE VIRUS. U. S. Bur. Plant Indus,, Plant Dis.

Rptr. 25: 3 61. [Processed.]

1942. INACTIVATING IN VIVO THE VIRUS OF X-DISEASE OF PEACH BY CHEMOTHERAPY.

(Abstract) Phytopathology 32: 17.

1944, IMMUNIZATION OF PEACH TREES TO X DISEASE BY CHEMOTHERAPY. (Abstract)

Phytopathology 34: 1011-1012.
VIRUS DISEASES OF STONE FRUITS 263

(226) STODDARD, E. M.

1^47. THE X DISEASE OF PEACH AND ITS CHEMOTHERAPY. Conn. (State) Agr.

Expt. Sta. Bui. 506, 19 pp.

(227) STOUT, G. L.

1939. PEACH MOSAIC. Calif. Dept. Agr. Bui. 28: 177-200, illus.

(228) and MCCLAIN, R. L.

1946. PEACH WART FOUND IN CALIFORNIA. U. S. Bur. Plant Indus., Soils, and

Agr. Engin., Plant Dis. Rptr. 30: 202-203. [Processed.].

(229) and WILSON, E. E.

1947. STUDIES OF A BUD FAILURE CONDITION IN ALMOND TREES. (Abstract) Phytopathology 37: 364.

(230) TAFT, L. R.

1911. REPORT OF THE STATE INSPECTOR OF NURSERIES AND ORCHARDS. Mich. State

Bd. Agr. Ann. Rpt. Sec. (1910-11) 50: 137-146.

(231) THOMAS, H. E.

1949. wiLLOA»^ TWIG OF PEACH AND NECTARINE. Calif. Fruit and Grape Grower

3 (7): 11, illus.

(232) and HILDEBRAND, E. M.

1936. A VIRUS DISEASE OF PRUNE. Phytopathology 26: 1145-1148, illus.

(23 3) — and RAWLINS, T. E.

1939. SOME MOSAIC DISEASES OF PRUNUS SPECIES. Hilgardia 12: 623-644, illus.

(234) RAWLINS, T. E., and PARKER, K. G.

1940. A TRANSMISSIBLE LEAF-CASTING YELLOWS OF PEACH. Phytopathology 30:

322-328, illus.

(23 5) SCOTT, C. E., WILSON, E. E., and FREITAG, J. H.

1944. DISSEMINATION OF A PEACH MOSAIC Phytopathology 34: 65 8-661, illus.

(236) THORNBERRY, H. H.

[1941.] VIRUS DISEASES OF THE PEACH. 111. State Flort. Soc. Trans. (1940) 74:

191-205, illus.

(237)

[1942.] DEVELOPMENTS IN PEACH VIRUS DISEASE INVESTIGATIONS. 111. State Hort,

Soc. Trans. (1941) 751 326-343, illus.

(238) TURNER, W. F.

193 3. PROGRESS IN PHONY PEACH DISEASE ERADICATION. Jour. Econ. Ent. 26:

659-667, illus.

(239)

(240)

193 5. PHONY PEACH DISEASE CONTROL IS PROMOTED BY DESTROYING WILD PEACH

TREES. U. S. Dept. Agr. Yearbook of Agr. 193 5: 275-277.

1949. INSECT VECTORS OF PHONY PEACH DISEASE. Science 109: 87-88.

(241) UNITED STATES PLANT QUARANTINE AND CONTROL ADMINISTRATION.

1929. QUARANTINE ON ACCOUNT OF THE PHONY PEACH DISEASE. NOTICE OF

QUARANTINE NO. 67. U. S. Plant Quar. and Control Admin., Serv. and

Régulât. Announc. 99, p. 118.

(242) VALLEAU, W. D.

1932. A VIRUS DISEASE OF PLUM AND PEACH. Ky. Agr. Expt. Sta. Bui. 327, pp.

r89]-103, illus.

(243) WAITE, M. B.

1930. THE PEACH YELLOWS GROUP OF DISEASES. Calif. Dept. Agr. Monthly Bui.

19: 484-488, illus.

(244) WALKER, E. A.

1939. RED SUTURE DISEASE OF PEACH REPORTED FROM MARYLAND. U. S. Bur. Plant

Indus., Plant Dis. Rptr. 23: 2 54. [Processed.]

(245) WIGHT, W. F.

1915. THE VARIETIES OF PLUMS DERIVED FROM NATIVE AMERICAN SPECIES. U. S.

Dept. Agr. Bui 172, 44 pp.

(246) WiLLisoN, R. S.

1944. STRAINS OF PRUNE DWARF,. Phytopathology 34: 1037-1049, illus.

(247)

(248)

1945. A LINE-PATTERN VIROSIS OF SHIRO PLUM. Phytopathology 3 5: 991-1001

illus.

1946. PEACH BLOTCH. Phytopathology 36: 273-276, illus.
264 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

(249) WiLLisoN, R. S., and BERKELEY, G. H.

1946. TATTER LEAF OF SWEET CHERRY, Phytopathology 56: 73-84, iílus.

(250) • BERKELEY, G. H., and CHAMBERLAIN, G. C.

1948. YELLOWS AND NECROTIC RING SPOT OF SOUR CHERRIES IN ONTARIO DISTRIBUTION AND SPREAD. Phytopathology 38: 776-792, illus.

(251) "WILSON, E. E., and STOUT, G. L.

1944. A BUD FAILURE DISORDER IN ALMOND TREES. Calif. Dcpt. Agr. BuL 33: 60-

64, illus.

(2 52) WISCONSIN AGRICULTURAL EXPERIMENT STATION.

1945. HOW IMPORTANT IS NECROTIC RING SPOT OF SOUR CHERRY? Wis. Agr. Expt.

Sta. Ann. Rpt. (Bui. 466) 61 (2): 23-24, illus.

(252a) WOLFE, H. R., ANTHON, E. W., and JONES, L. S.

19 5 0. TRANSMISSION OF WESTERN X-DISEASE OF PEACHES BY THE LEAFHOPPER, COLLADONUS GEMINATUS (VAN D.) (Abstract) Phytopathology 40: 971.

(253) WOOD, J. I., STEVENS, N. E., and MILLER, P. R., compilers,

193 3. DISEASES OF PLANTS IN THE UNITED STATES IN 1932. [U. S. Bur. Plant

Indus.], Plant Dis. Rptr. Sup. 8 5, 82 pp., illus. [Processed.]

(254) WRIGHT, C. M., BLODGETT, E. C, REEVES, E. L., and WILLIAMS, H. E.

1948. THE 1948 LITTLE CHERRY AND WESTERN X DISEASE SURVEY. Wash. State

Elort. Assoc. Proc. 44: [227]-231.

(255) ZELLER, S. M.

1934. CHERRY MOTTLE LEAF. Greg. State Hort. Soc. Ann. Rpt. 26: 92-9S, illus.

(256)

1942, VIRUS DISEASES OF STONE FRUITS. Greg. State Hort. Soc. Ann. Rpt. 34:

[8 5]-90, illus.

(257) and CORDY, C. B.

1942. BUCKSKIN DISEASE OF CHERRY IN SOUTHERN OREGON. U. S. Bur. Plant Indus.,

Plant Dis. Rptr. 26: 141. [Processed.]

(25 8) and EVANS, A. W.

1941. TRANSMISSION OF WESTERN X-DISEASE AND MARGINAL LEAF SPOT OF PEACH

IN OREGON. U. S. Bur. Plant Indus., Plant Dis. Rptr. 25: 452-45 3.

[Processed.]

(2 59) and EVANS, A. W.

1941. VEIN CLEARING, A TRANSMISSIBLE DISEASE OF PRUNUS. Phytopathology 31:

463-4^7, illus.

(260) ' KIENHOLZ, J. R., and OWENS, C. E.

1942. WESTERN X-DISEASE OF PEACH IN OREGON. U. S. Bur. Plant Indus., Plant

Dis. Rptr. 26: 13 8-141, illus. [Processed.]

(261) and MILBRATH, J. A.

1942. BANDED CHLOROSIS, A TRANSMISSIBLE DISEASE OF CHERRY. Phytopathology 32:

634-63 5, illus.

(262) and MILBRATH, J. A.

1945. TRANSMISSION OF PEACH WART TO SWEET CHERRY. Phytopathology 3 5: 607-

609, illus.

(263) and MILBRATH, J. A.

1946. VIRUS DISEASES OF STONE FRUIT TREES AND BUD WOOD SELECTION. Oreg. State

Hort. Soc. Ann. Rpt. 38: [5 5]-57.

(264) and MILBRATH, J. A.

1947. MILD RUSTY MOTTLE OF SWEET CHERRY (PRUNUS AVIUM). Phytopathology

37: 77-84, illus.

(265) and MILBRATH, J. A.

1948. WESTERN X-DTSEASE OF MONTMORENCY CHERRY AND ITS RELATION TO BUCKSKIN OF SWEET CHERRY, (Abstract) Phytopathology 38: 920.

(265a) and MILBRATH, J. A.

1950. THE RECOVERY OF WESTERN X-DISEASES OF PEACH FROM MONTMORENCY

CHERRY AND ITS RELATION TO BUCKSKIN OF SWEET CHERRY. Phytopathology

40: 707-711, illus.

(266) MILBRATH, J. A., and CORDY, C. B,

1944. ALBINO CHERRY, A VIRUS DISEASE IN SOUTHERN OREGON. (Abstract) Pkytopathology 34: 937.

(267) MILBRATH, J. A,, and KIENHOLZ, J. R.

1947. BLACK CANKER OF CHERRY. (Abstract) Phytopathology 37: 366.
VIRUS DISEASES OF STONE FRUITS 265

(268) ZuNDEL, G. L.

1944. EASTWARD EXTENSION OF PEACH X-DISEASE ON CHOKECHERRY IN PENNSYLVANIA. U. S. Bur, Plant Indus., Soils, and Agr. Engin., Plant Dis. Rptr. 28:

894-895. [Processed.]

DEFICIENCY AND EXCESS TROUBLES THAT RESEMBLE

VIRUS DISEASES ^^

(269) ANDERSSEN, F. G.

1932. CHLOROSIS OF DECIDUOUS FRUIT TREES DUE TO A COPPER DEFICIENCY. JOUR,

Pomol, and Hort. Sei. 10: 130-146, illus.

(270) BENNETT, J. P.

1931. THE TREATMENT OF LIME-INDUCED CHLOROSIS WITH IRON SALTS. Calif. Agr.

Expt. Sta. Cir. 321, 12 pp., illus.

(271)

1945. IRON IN LEAVES. Soil Sei. 60: 91-105.

(272) BLAKE, M. A.

[1922.] EFFECT OF AN EARLY APPLICATION OF NITROGEN ON PEACH TREES DEFICIENT

IN VIGOR. Amcr. Soc. Hort. Sei. Proc. (1921) 18: 139-143.

(273) BLODGETT, E. C.

1941. A SYSTEMIC ARSENIC TOXTCITY OF PEACH AND APRICOT ON OLD APPLE LAND.

U. S. Bur. Plant Indus., Plant Dis. Rptr. 25: 549-5 51. [Processed.]

(274)

1946. CHLOROSIS OF PLANTS IN IDAHO. Idaho Agr, Expt. Sta. Cir. 110, 7 pp.

(275) BOYNTON, D.

1944. RESPONSES OF YOUNG ELBERTA PEACH AND MONTMORENCY CHERRY TREES

TO POTASSIUM FERTILIZATION IN NEW YORK. Amer. Soc. Hort. Sci. Proc.

44: 31-33.

(276)

1947. MAGNESIUM NUTRITION OF APPLE TREES. Soil Sci. 63: 53-58.

(277) REUTHER, W., and CAIN, J. C.

1941. LEAF ANALYSIS AND APPARENT RESPONSE TO POTASSIUM IN SOME PRUNE

AND APPLE ORCHARDS, PRELIMINARY REPORT. Amer. SoC. Hort. Sci. PrOC.

38: 17-20, illus.

(277a) BULLOCK, R. M., and BENSON, N. R.

1948. BORON DEFICIENCY IN APRICOTS. Amer. Soc. Hort. Sci. Proc. 51: 199-204,

illus,

(278) BURRELL, A. B.

1937. BORON TREATMENT FOR A PHYSIOGENIC APPLE DISEASE. Amcr. SoC. Hort.

Sei. Proc. (1936) 34: 199-205.

(279) CAMP, A. F., CHAPMAN, H. D., and PARKER, E. R.

1949. SYMPTOMS OF CITRUS MALNUTRITION. In Amer. Soc. Agron. and Nati. Pert.

Assoc., Hunger Signs in Crops, Ed. 2, pp. 3 07-365, illus.

(280) CHANDLER, W. H.

1937. ZINC AS A NUTRIENT FOR PLANTS. Bot. Gaz. 98: 625-646, illus.

(281) HOAGLAND, D. R., and HIBBARD, P. L.

1932. LITTLE-LEAF OR ROSETTE IN FRUIT TREES. Amer. Soc. Hort. Sei. Proc. (1931)

28: 556-560, illus.

(282) HOAGLAND, D. R., and HIBBARD, P. L.

193 3. LITTLE-LEAF OR ROSETTE OF FRUIT TREES, ii: EFFECT OF ZINC AND OTHER

TREATMENTS. Amer. Soc. Hort. Sci. Proc. (1932) 29: 255-263, illus.

(282a) CHILDERS, N. F.

1950. MINOR ELEMENTS: MAJOR PROBLEM IN ORCHARDS. N. J. Farm and Garden

21 (12): 10-11, 46, illus.

(283) CuLLiNAN, F. P., and BATJER, L. P.

1945. NITROGEN, PHOSPHORUS, AND POTASSIUM INTERRELATIONSHIPS IN YOUNG

PEACH AND APPLE TREES. Soil Sci. 55: 49-60, illuS.

(284) and WAUGH, J. G.

1940. RESPONSE OF PEACH TREES TO POTASSIUM UNDER FIELD CONDITIONS. Amer.

Soc, Hort. Sci. Proc, (1939) 37: 87-94, illus.

^References (139) and (187) also are applicable.
266 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

(28 5) DAVIDSON, O. W., and JUDKINS, W. P.

1949. NUTRIENT-DEFICIENCY SYMPTOMS IN DECIDUOUS FRUITS. In Amer. Soc. Agron.

and Nati. Fert. Assoc, Hunger Signs in Crops, Ed. 2, pp. 215-267, illus.

(286) DICKEY, R. D., and BLACKMON, G. H.

1940. A PRELIMINARY REPORT ON LITTTE-EEAF OF THE PEACH IN FLORIDA A

ZINC DEFICIENCY. Fla. Agr. Expt. Sta. Bui. 344, 19 pp., illus.

(287) DuNBAR, C. O., and ANTHONY, R. D.

193 8. TWO CASES OF POTASSIUM DEFICIENCY IN PEACH ORCHARDS IN SOUTH CENTRAL

PENNsyLVANiA. Amcr. Soc. Hort. Sei. Proc. (1937) 35: 320-325, illus.

(2 88) EATON, F. M.

193 5. BORON IN SOILS AND IRRIGATION WATERS AND ITS EFFECT ON PLANTS, WITH

PARTICULAR REFERENCE TO THE SAN JOAQUíN VALLEY OF CALIFORNIA.

U. S. Dept. Agr. Tech. Bui. 448, 132 pp., illus.

(289)

1944. DEFICIENCY, TOXICITY, AND ACCUMULATION OF BORON IN PLANTS. Jour.

Agr. Res. 69: 237-277, illus.

(290) MCCALLUM, R. D., and MAYHUGH, M. S.

1941. QUALITY OF IRRIGATION WATERS OF THE HOLLISTER AREA OF CALIFORNIA

WITH SPECIAL REFERENCE TO BORON CONTENT AND ITS EFFECT ON APRICOTS

AND PRUNES. U. S. Dcpt. Agr. Tech. Bui. 746, 60 pp., illus.

(291) EPSTEIN, E., and LILLELAND, O.

1942. A PRELIMINARY STUDY OF THE MANGANESE CONTENT OF THE LEAVES OF

SOME DECIDUOUS FRUIT TREES. Amcr. Soc. Hort. Sei. Proc. 41: 11-18,

illus.

(291a) FiTZPATRicK, R. E., and WOODBRIDGE, C. G.

1941. BORON DEFICIENCY IN APRICOTS. Sci. Agr. 22: 271-273, illus.

(292) HAAS, A. R. C.

1942. LIME-INDUCED CHLOROSIS OF CITRUS IN RELATION TO SOIL FACTORS. Plant

Physiol. 17: 27-51.

(293) HANSEN, C. J,

1945. THE EFFECT OF BORON ON DECIDUOUS FRUIT TREES. BluC Anchor 22 (4):

12-15, illus.

(294) and PROEBSTING, E. L.

1949. BORON REQUIREMENTS OF PLUMS. Amer, Soc. Hort. Sei. Proc. 53: 13-20,

illus,

(29 5) HARLEY, C. P.

1947. MAGNESIUM DEFICIENCY IN KIEFFER PEAR TREES. Amer. SoC. Hort. Sci. PrOC.

50: 21-22, illus.

(296) HoAGLAND, D. R., and CHANDLER, W. H,

193 3. SOME EFFECTS OF DEFICIENCIES OF PHOSPHATE AND POTASSIUM ON THE

GROWTH AND COMPOSITION OF FRUIT TREES, UNDER CONTROLLED CONDITIONS. Amer. Soc. Hort. Sci. Proc. (1932) 29: 267-271, illus.

(297) CHANDLER, W. H., and HIBBARD, P. L.

1936. LITTLE-LEAF OR ROSETTE OF FRUIT TREES, V. EFFECT OF ZINC ON THE

GROWTH OF PLANTS OF VARIOUS TYPES IN CONTROLLED SOIL AND WATER

CULTURE EXPERIMENTS. Amer. Soc. Hort. Sci. Proc. (1935) 33: 131-141,

illus.

(298) JACOBSON, L.

1945. IRON IN THE LEAVES AND CHLOROPLASTS OF SOME PLANTS IN RELATION TO

TFIEIR CHLOROPHYLL CONTENT. Plant Physiol. 20: 23 3-245, illus.

(299) LiLLELAND, O.

193 3. EXPERIMENTS IN K AND P DEFICIENCIES WITH FRUIT TREES IN THE FIELD.

Amer, Soc. Hort. Sci. Proc. (1932) 29: 272-276, illus.

(300)

1946. THE PRESENT STATUS OF LEAF ANALYSES IN RELATION TO FRUIT TREE NUTRITION. Blue Anchor 23 (1): 14-16, 2 8-31, illus.

(301) — BROWN, J. G., and CONRAD, J. P.

1942. THE PHOSPHATE NUTRITION OF FRUIT TREES III. COMPARISON OF FRUIT TREE

AND FIELD CROP RESPONSES ON A PHOSPHATE DEFICIENT SOIL. Amer. SoC.

Hort. Sci. Proc. 40: 1-7, illus.

(3 02) BROWN, J. G., and SWANSON, C.

1945. RESEARCH SHOWS SODIUM MAY CAUSE LEAF TIP BURN. Almond Facts 9 (2):

1, 5, illus.
VIRUS DISEASES OF STONE FRUITS 267

(303) LINDNER, R. C.

1943. ARSENIC INJURY OF PEACH TREES. Amer. Soc. Hort. Sei. Proc. 42: 275-279,

illus.

(304) MCLARTY, H. R., and WOODBRIDGE, C. G.

1949. BORON IN RELATION TO THE CULTURE OF THE PEACH TREE. (Abstract)

Phytopathology 39: 860-861.

(305) MAGNESS, J. R., DEGMAN, E. S., BATJER, L. P., and REGEIMBAL, L, O.

1937. EFFECT OF NUTRITIONAL TREATMENTS ON INTERNAL CORK OF APPLES. Amer.

Soc. Hort. Sei. Proc. (1936) 34: 206-209, illus.

(3 06) MORRIS, O. M.

193 8. THE TOLERANCE OF VARIOUS ORCHARD COVER CROPS TO ARSENICAL TOXïCITY

IN THE SOIL, Wash. State Hort. Assoc. Proc. 34: 110-112.

(307) PROEBSTING, E. L.

1937. FERTILIZING DECIDUOUS FRUIT TREES IN CALIFORNIA. Calif. Agr. Expt. Sta.

Bul. 610, 29 pp., illus.

(308) and KINMAN, C. F.

1934. ORCHARD TRIALS OF NITROGEN AND PHOSPHORUS. Amcr. SoC. Hort. Sci.

Proc. (1933) 30: 426-430, illus.

(309) RAWL, E. H.

193 6. PEACH TREE ABNORMALITIES DEVELOPING FROM APPLICATIONS OF NITROGEN

FERTILIZERS ALONE. Amer. Soc. Hort. Sei. Proc. (193 5) 33: 293-298.

(310) and STALLWORTH, W. H.

1935. PEACH TREES IN SOUTH CAROLINA DEVELOP ABNORMALITIES WITH NITROGEN

FERTILIZATION ALONE. Clemson Agr. Col. S. C, Hort. Cir. 10, 22 pp.,

illus. [Processed.]

(311) SCHUSTER, C. E., MCWHORTER, O. T., and STEPHENSON, R. E.

1939. RESPONSE OF FRUIT TREES NEAR THE DALLES, OREGON, TO APPLICATIONS OF

BORON AND ZINC. Amer. Soc. Hort, Sei. Proc. (1938) 36: 99-101.

(312) SCOTT, L. E.

1939. RESPONSE OF PEACH TREES TO POTASSIUM AND PHOSPHORUS FERTILIZERS

IN THE SANDHILL AREA OF THE SOUTHEAST. Amer. SoC. Hort. Sci. ProC.

(1938) 36: 56-60.

(313) SMITH, R. E., and THOMAS, H. E.

192 8. COPPER SULPHATE AS A REMEDY FOR EXANTHEMA IN PRUNES, APPLES, PEARS,

AND OLIVES. Phytopathology 18: 449-454, illus.

(314) THOMPSON, A. H., and BATJER, L. P.

1948. HELPFUL SOIL TREATMENT FOR CORRECTING ARSENIC INJURY TO PEACH

TREES PLANTED ON TOXIC SOILS. Wash. State Hort. Assoc. Proc. 44:

[207]-208.

(315) THORNE, D. W., and WANN, F. B.

1949. THE ZINC PROBLEM IN UTAH ORCHARDS. Farm 8c Home Sci, [Utah Agr.

Expt. Sta.] 10 (4): 10-12, illus.

(315a) and WANN, F. B.

1950. NUTRIENT DEFICIENCIES IN UTAH ORCHARDS. Utah Agr. Expt. Sta. Bui. 33 8,

29 pp., illus.

(316) VANDECAVEYE, S, C, HORNER, G. M., and KEATON, C. M.

1936. UNPRODUCTIVENESS OF CERTAIN ORCHARD SOILS AS RELATED TO LEAD ARSENATE

SPRAY ACCUMULATIONS. Soil Sei. 42: 203-215, illus.

(317) WALLACE, T.

1928. LEAF scoRCEi OF FRUIT TREES. Jour. Pomol. and Hort. Sei. 6: 243-281,

illus.; 7: ri]-31, illus.

(318)

(319)

1929. INVESTIGATIONS ON CHLOROSIS OF FRUIT TREES. IV. THE CONTROL OF LIMEINDUCED CHLOROSIS IN THE FIELD. Jour. Pomol. and Hort. Sei. 7: 2 51-269.

1944. THE DIAGNOSIS OF MINERAL DEFICIENCIES IN PLANTS BY VISUAL SYMPTOMS.

Ed. 2, 116 pp., 114 col. pis., with new "'Supplement" included in 1-vol. ed.,

[5 8] pp., 95 col. pis, London.

(320) WANN, F. B.

193 0. CHLOROSIS: YELLOWING OF PLANTS. Utah Agr. Expt. Sta. Cir. 8 5, 12 pp.,

illus.
268 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

(321) WANN, F. B., and THORNE, D. W.

19 Î0. ZINC DEFICIENCY OF PLANTS IN THE WESTERN STATES. Sci. Monthly 70:

180-184, illus.

(322) WEINBERGER, J. H., and CULLINAN, F. P.

1937. SYMPTOMS OF SOME MINERAL DEFICIENCIES IN ONE-YEAR ELBERTA PEACH

TREES. Amer. Soc. Hort. Scî. Proc. (1936) 34: 249-254, illus.
APPENDIX

COMMON AND SCIENTIFIC NAMES OF PLANTS

Almond {Prunus amygdalus Batsch; syn, P.

communis (L.) Arcang.)

Almond, desert (P. fasciculata (Torr.) Gray)

Almond, fenzl (P. fenzliana Fritscli)

Almond, tangut (P. tangtitica Batal.)

Apple (Malîis sylvesfris Mill.)

Apricot {Vrunus armeniaca L.)

Apricot, ansu (P. armeniaca var. ansu Maxim.)

Apricot, desert (P. fremontii S. Wats.)

Apricot, Japanese (P. mume (Sieb.) Sieb. &

Zuce.)

Bushcherry, Chinese (P. japónica Thunb.)

Carrot {Daucus carota L.)

Cherry, almond {Prtmus glandtdosa Thunb.)

Cherry, Bessey (P. besseyi Bailey)

Cherry, bitter (P. emarginata (Dougl.) Walp.)

Cherry, bitter (var. mollis) (P. ejnarginata

var. mollis (Dougl.) Brewer & Wats.)

Cherry, black (P. serótina Ehrh.)

Cherry, duke (P. avium X JP« cerasus)

Cherry, Hansen bush (P. besseyi Bailey)

Cherry, hollyleaf (P. ilicifolia (Nutt.) Walp.)

Cherry, mahaleb (P. mabaleb L.)

Cherry, Manchu (P. tomentosa Thunb.)

Cherry, mazzard (P. avium L.)

Cherry, oriental flowering (P. serrulafa Lindl.)

Cherry, pin (P. pensylvanica L.)

Cherry, sand (P. pumila L.)

Cherry, sour (P. cerasus L.)

Cherry, sweet (P. avjîtvi L.)

Chokecherry, common, or eastern (P. virginiana L.)

Chokecherry, western (P. virginiana var. í/íwmö (Nutt.) Torr.; syn. P. demissa (Nutt.)

D. Dietr.)

Cucumber {Cucumis saiivus L.)

Kerria, Japanese (Kerria japónica (L.) DC.)

Laurelcherry, Portuguese (Prunus lusitantca

L.)

Mazzard (P. avium L.)

Nectarine (P. pérsica var. nectarina Ait.)

Maxim.; syn. P. pérsica var. nucipersica

(Borkh.) Schneid.)

Parsley {Petroselimim crisptim (Mill.) Nym.)

Peach (Prunus pérsica (L.) Batsch)

Peach, David (P. davidiana (Carr.) Franch.)

Peach, desert (P. andersonii Gray)

Peach, purple-leaved (P. pérsica var. atropurpîirea Schneid.)

Peach, smoothpit (P. w/ríí Koehne)

Pear (Pyrtis com^munis L.)

Periwinkle (Vinca rosea L.)

Plum, American (Prunus americana Marsh.)

Plum, apricot (P. si^nonii Carr.)

Plum, Bokar (P. bokhariensis Schneid.)

Plum, beach (P. maritima Marsh.)

Plum, chickasaw (P. angusfifolia Marsh.)

Plum, damson type, or buUace (P. insititia L.)

Plum, domestica, or garden (P. domestica L.)

Plum, flatwoods (P. umbellata Ell.)

Plum, hog (P. reverchonii Sarg.)

Plum, hortulan (P. hortulana Bailey)

Plum, Indian (Osmaronia cerasiformis (Torr.

& Gray) Greene)

Plum, Japanese (Prunus salicina Lindl.)

Plum, klamath (P. subcordata Benth.)

Plum, Mexican (P. inexicana S. Wats.)

Plum, myrobalan (P. cerasifera Ehrh.)

Plum, pottawattamie, or wildgoose (P. munsoniana Wight & Hedr.)

Plum, purple, or ornamental (P. cerasifera var.

atropurpúrea Jaeger; syn. P. cerasifera var.

pissardi (Carr.) Bailey)

Plum, wildgoose (P. mtutsoniana Wight &

Hedr.)

Prune (P. domestica L.)

Tobacco (Nicotiana glutinosa L.)

Tomato (Lycopersicon esculentum Mill.)

269
LIST OF AUTHORS

C. W. Bennett, Division of Sugar Plant Investigations, Bureau of Plant Industry, Soils, and

Agricultural Engineering, U. S. Department of Agriculture, Riverside, Calif.

J. P. Bennett, Division of Plant Nutrition, California Agricultural Experiment Station, Berkeley, Calif.

G, H. Berkeley, Dominion Laboratory of Plant Pathology, St. Catharines, Ontario, Canada.

M. A. Blake,^^ formerly Department of Horticulture, New Jersey Agricultural Experiment

Station, New Brunswick, N. J.

Earle C. Blodgett, Department of Plant Pathology, Washington Agricultural Experiment

Station, Prosser, Wash.

E. W. Bodine, formerly Department of Botany and Plant Pathology, Colorado Agricultural

Experiment Station, Fort Collins, Colo.

Damon Boynton, Department of Horticulture and Allied Branches, New York (Cornell)

Agricultural Experiment Station, Ithaca, N. Y,

Donald Cation, Department of Botany and Plant Pathology, Michigan Agricultural Experiment Station, East Lansing, Mich.

W". H. Chandler, emeritus. Division of Horticulture, California Agricultural Experiment

Station, Los Angeles, Calif.

C. N. Clayton, Department of Botany, North Carolina Agricultural Experiment Station,

Raleigh, N. C.

L. C. Cochran, Division of Fruit and Vegetable Crops and Diseases, Bureau of Plant Industry,

Soils, and Agricultural Engineering, U. S. Department of Agriculture, Citrus Experiment

Station, Riverside, Calif.

C. B. Cordy, County Agricultural Agent, Medford, Oreg.

F. P. Cullinan, Bureau of Plant Industry, Soils, and Agricultural Engineering, U. S. Department of Agriculture, Plant Industry Station, Beltsville, Md.

O. W. Davidson, Department of Horticulture, New Jersey Agricultural Experiment Station,

New Brunswick, N. J.

L. W. Durrell, Department of Botany and Plant Pathology, Colorado Agricultural Experiment

Station, Fort Collins, Colo.

W. R. Foster, British Columbia Department of Agriculture, Parliament Buildings, Victoria,

British Columbia, Canada.

Carl J. Hansen, Division of Pomology, California Agricultural Experiment Station, Davis, Calif,

C. P. Harley, Division of Fruit and Vegetable Crops and Diseases, Bureau of Plant Industry,

Soils, and Agricultural Engineering, U. S. Department of Agriculture, Plant Industry

Station, Beltsville, Md.

A. Leon Havis, Division of Fruit and Vegetable Crops and Diseases, Bureau of Plant Industry,

Soils, and Agricultural Engineering, U. S. Department of Agriculture, Plant Industry

Station, Beltsville, Md.

W. B. Hewitt, Division of Plant Pathology, California Agricultural Experiment Station,

Davis, Calif.

E. M. Hildebrand, Department of Plant Physiology and Pathology, Texas Agricultural and

Mechanical College, College Station, Tex.

Lee M. Flutchins, Division of Forest Pathology, Bureau of Plant Industry, Soils, and Agricultural Engineering, U. S. Department of Agriculture, Plant Industry Station, Beltsville,

Md.

G. W, Keitt, Department of Plant Pathology, Wisconsin Agricultural Experiment Station,

Madison, Wis.

J. R. Kienholz, Division of Fruit and Vegetable Crops and Diseases, Bureau of Plant Industry,

Soils, and Agricultural Engineering, U. S, Department of Agriculture, Fruit Disease Field

Laboratory, Hood River, Oreg.

C. F. Kinman, Division of Fruit and Vegetable Crops and Diseases, Bureau of Plant Industry,

Soils, and Agriculttird Engineering, U. S. Department of Agriculture, Plant Industry Station, Beltsville, Md.

*^ Deceased.

270
VIRUS DISEASES OF STONE FRUITS 271

L. O. Kunkel, emeritus, Rockefeller Institute for Medical Research, 66th and York Avenue,

New York 21, N. Y.

Omund Lilleland, Division of Pomology, California Agricultural Experiment Station, Davis,

Calif.

T. B. Lott, Dominion Laboratory of Plant Pathology, Summeriand, British Columbia, Canada.

J. A. McClintock, Department of Horticulture, Indiana Agricultural Experiment Station,

Lafayette, Ind.

H. R. McLarty, Dominion Laboratory of Plant Pathology, Summerland, British Columbia,

Canada.

T. F. Manns, formerly Department of Plant Pathology and Soil Bacteriology, Delaware Agricultural Experiment Station, Newark, Del.

J. A. Milbrath, Department of Botany and Plant Pathology, Oregon Agricultural Experiment

Station, Corvallis, Oreg.

J. Duain Moore, Department of Plant Pathology, Wisconsin Agricultural Experiment Station,

Madison, Wis.

D. H. Palmiter, Division of Plant Pathology, New York State Agricultural Experiment

Station, Poughkeepsie, N. Y.

K. G. Parker, Department of Plant Pathology, New York (Cornell) Agricultural Experiment

Station, Riverhead. N. Y.

G. L. Philp,^^ formerly Division of Pomology, California Agricultural Experiment Station,

Davis, Calif.

E. L. Proebsting, Division of Pomology, California Agricultural Experiment Station, Berkeley,

Calif.

E. J. Rasmussen, Department of Horticulture, New Hampshire Agricultural Experiment Station, Durham, N. H.

T. E. Rawlins, Division of Plant Pathology, California Agricultural Experiment Station,

Berkeley, Calif.

E. L. Reeves, Division of Fruit and Vegetable Crops and Diseases, Bureau of Plant Industry,

Soils, and Agricultural Engineering, U. S. Department of Agriculture, Horticultural Field

Laboratory, Wenatchee, Wash.

B. L. Richards, Department of Botany and Plant Pathology, Utah Agricultural Experiment

Station, Logan, Utah.

C. O. Smith, emeritus, California Agricultural Experiment Station, Citrus Experiment Station, Riverside, Calif.

Ralph E. Smith, Division of Plant Pathology, California Agricultural Experiment Station,

Berkeley, Calif.

E. M. Stoddard, Department of Plant Pathology and Botany, Connecticut State Agricultural

Experiment Station, New Haven, Conn.

Gilbert L. Stout. Department of Plant Pathology, California State Department of Agriculture,

Sacramento, Calif.

H. Earl Thomas, Division of Plant Pathology, California Agricultural Experiment Station,

Berkeley, Calif.

H. H. Thornberry, Department of Horticulture, Illinois Agricultural Experiment Station,

Urbana, 111.

William F. Turner, Division of Fruit Insect Investigations, Bureau of Entomology and Plant

Quarantine, U. S. Department of Agriculture, Fort Valley, Ga.

M. F. Welsh, Dominion Laboratory of Plant Pathology, Summerland, British Columbia,

Canada.

R. S. Willison, Dominion Laboratory of Plant Pathology, St. Catharines, Ontario, Canada,

E. E. Wilson, Division of Plant Pathology, California Agricultural Experiment Station, Davis,

Calif.

S. M. 2eller,'^° formerly Department of Botany and Plant Pathology, Oregon Agricultural

Experiment Station, Corvallis, Oreg.

*® Deceased.
REFERENCES TO VIRUS DISEASES DESCRIBED TOO LATE FOR

INCLUSION OF SECTIONS

Peach :

Yellow leaf roll—

NYLAND, G., and SCHLOCKER, A.

1951. YELLOW LEAF ROLL OF PEACH. U. S. Bur. Plant Indus., Soils, and Agr. Engin.,

Plant Dis. Rptr. 3Î: 33. [Processed.]

Sweet cherry:

Cherry bark blister—

STOUT, G. L.

1949. CHERRY BARK BLISTER. Calif. Dept. Agr. Bui. 38; 2 57-260.

Dixie rusty mottle—

RICHARDS, B. L., and WADLEY, B. N.

19 50. UTAH DIXIE RUSTY MOTTLE OF SWEET CHERRY. (Abstract) Phytopathology 40:

969,

WADLEY, B. N., and COCHRAN, G, W.

1950. NEW VIRUS DISEASE OF SWEET CHERRIES FOUND IN UTAH'S DIXIE. Farm & Home

Sei. [Utah Agr. Expt. Sta.] 11: 36-37, illus.

Mild rugose mosaic—

BERKELEY, G. H.

1950. MILD RUGOSE MOSAIC OF SWEET CHERRY. Phytopathology 40: 992-998, illus.

272
HOST-DISEASE INDEX"

Page

Almond

Almond bud failure 20S

Almond calico 189

Asteroid spot 84

Boron-excess injury 246

Buckskin 98

Cherry rugose mosaic 139

Drake almond bud failure 191

Iron chlorosis 23 0

Manganese deficiency 235

Muir peach dwarf 64

Nitrogen deficiency 222

Peach mosaic 27

Peach rosette 7

Peach yellows 1

Phony , 18

Ring spot 72

Sodium-excess injury 249

X-disease 38

Yellow bud mosaic 53

Zinc deficiency 237

Almond, desert

Yellow bud mosaic 53

Almond hybrids

Buckskin 98

Almond, tangut

Peach mosaic 27

Ring spot 72

Apple

Ring spot 72

Apricot

Arsenic injury 250

Asteroid spot 84

Boron deficiency 244

Boron-excess injury 246

Copper deficiency 241

Golden-net , g g

Iron chlorosis 230

Line pattern Ijg

Little peach 4

Manganese deficiency 23 5

Muir peach dwarf 64

Peach mosaic 27

Peach rosette 7

Peach yellows 1

Phony 18

Prune dwarf 171

Ring pox 187

Ring spot 72

Sodium-excess injury 249

Western X-disease 46

Page

Apricot—Con.

Yellow bud mosaic 53

Zinc deficiency 237

Apricot, ansu

Asteroid spot 84

Apricot, desert

Ring spot 72

Apricot, Japanese

Asteroid spot 84

Peach mosaic 27

Peach yellows 3

Phony 18

Ring spot 72

Yellow bud mosaic 5 3

Bushcherry, Chinese

X-disease 3 8

Carrot

X-disease 38

Cherry, almond

Peach yellows 3

Cherry, Bessey

Necrotic ring spot 164

Peach mosaic 27

Western X-disease 46

X-disease 38

Cherry, bitter

Buckskin 98

Mottle leaf 107

Cherry, black

Sour cherry yellows 153

Cherry, duke

See cherry hybrids.

Cherry hybrids

Mottle leaf 106

Necrotic ring spot 164

Peach mottle 59

Sour cherry yellows 153

Cherry, mahaleb

Buckskin 98

Cherry rugose mosaic 139

Green ring mottle 159

Line pattern I77

Mottle leaf 107

Muir peach dwarf 64

Necrotic ring spot . 164

Prune dwarf I71

Ring spot 72

Sour cherry yellows 153

Tatter leaf . . . , 141

•^^ Host here includes suscept of nontransmissible diseases and species affected with nutritional

disorders.

273
274 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Page

Cherry, Manchu

Peach mosaic 27

Peach yellows 3

Ring spot 71

Western X-disease 46

Cherry, mazzard

See sweet cherry.

Cherry, oriental flowering

Line pattern . 177

Ring spot 72

Rough bark 149

Rusty mottle (severe) 119

Cherry, pin

Necrotic ring spot 164

Sour cherry yellows 1Î3

Cherry, sand

Necrotic ring spot 164

Peach rosette 7

Ring spot 72

Cherry, sour

Albino 103

Buckskin 58

Green ring mottle 159

Iron chlorsis 230

Line pattern 177

Little cherry 126

Manganese deficiency 235

Mild rusty mottle Ho

Mottle leaf 106

Necrotic ring spot 164

Peach mottle 59

Peach rosette . 7

Pink fruit 162

Potassium deficiency 224

Prune dwarf 171

Rasp leaf 132

Ring spot 72

Rusty mottle 113

Sour cherry yellows 152

Tatter leaf 141

Twisted leaf 13 5

Western X-disease . 46

X-disease 38

Zinc deficiency 237

Cherry, sweet

Albino 103

Almond calico 189

Arsenic injury 250

Blank canker 137

Boron deficiency 244

Boron-excess injury 246

Buckskin 98

Cherry bark blister . 272

Cherry rugose mosaic 139

Dixie rusty mottle 272

Green ring mottle 159

Iron chlorosis 230

Lambert mottle 123

Line pattern 177

Little cherry 126

Manganese deficiency 235

Mild rugose mosaic 272

Mild rusty mottle 116

Page

Cherry, sweet—Con.

Mottle leaf 106

Muir peach dwarf 64

Necrotic ring spot 164

Necrotic rusty mottle 120

Peach mottle 'i^

Peach necrotic leaf spot 81

Peach rosette 7

Pinto leaf 147

Prune dwarf 171

Rasp leaf 132

Ring spot 72

Rough bark of oriental flowering

cherry 149

Rusty mottle 112

Small bitter cherry 130

Sodium-excess injury 249

Sour cherry yellows 153

Sweet cherry crinkle leaf 195

Sweet cherry deep suture 201

Tatter leaf 141

Twisted leaf 135

Wart '>6

Western X-disease 46

X-discase 3 8

Yellow bud mosaic 53

Zinc deficiency 237

Chokecherry, common, or eastern

Necrotic ring spot 164

Ring spot 72

Sour cherry yellows 153

Western X-disease 43

X-disease 3 8

Chokecherry, western

Buckskin 98

Ring spot 72

Rusty mottle (severe) 119

Western X-disease 46

Cucumber

Necrotic ring spot 164

Hybrids

See various plants.

Kerria, Japanese

Yellow bud mosaic 5 3

Laurelcherry, Portuguese

Yellow bud mosaic 53

Mazzard

See sweet cherry.

Nectarine

Asteroid spot , . . . , 84

Peach mosaic 27

Peach yellows 1

Willow twig 95

Western X-disease 46

X-disease 3 8

Parsley

X-disease 3 8

Peach

Almond calico 189

Arsenic injury 250

Asteroid spot 84

Boron deficiency 244

Boron-excess injury 246
VIRUS DISEASES OF STONE FRUITS 275

Peach—Con.

Buckskin 98

Calcium deficiency 243

Cherry rugose mosaic 139

Copper deficiency 241

Golden-net 88

Green ring mottle 159

Iron chlorosis 230

Line pattern 177

Little peach 4

Magnesium deficiency 234

Manganese deficiency 235

Mild rusty mottle 116

Mottle leaf 107

Muir peach dwarf 63

Necrotic ring spot 164

Nitrogen deficiency 222

Peach blotch 93

Peach cahco 90

Peach mosaic 26

Peach mottle $9

Peach necrotic leaf spot 81

Peach rosette 7

Peach variegation 213

Peach yellows 1

Phony 17

Phosphorus deficiency 228

Potassium deficiency . , 224

Prune dwarf 171

Red suture . 11

Ring spot , 71

Rosette mosaic 14

Rough bark of oriental flowering

cherry 149

Rusty mottle 113

Sodium-excess injury 249

Sour cherry yellows 153

Standard prune constricting mosaic. 185

Tatter leaf 141

Twisted leaf 135

Wart 56

"Western X-disease 43

Willow twig 9 5

X-disease 37

Yellow bud mosaic 5 3

Yellow leaf roll 272

2inc deficiency . 237

Peach, David

Peach mosaic 27

Peach yellows 3

Phony 18

Ring spot 72

Peach, desert

Yellow bud mosaic 53

Peach hybrids

Buckskin 98

Peach, purple-leaved

X-disease 38

Peach, smoothpit

Buckskin 98

Periwinkle

Peach rosette 7

X-disease 3 8

Page

Plum, American

Necrotic ring spot 164

Peach mosaic 27

Peach yellows 1

Ring spot 72

Sour cherry yellows 153

X-disease 38

Plum, Bokar

Peach mosaic 27

Ring spot 72

Plum, chickasaw

Peach mosaic 27

Peach rosette 7

Phony 18

Ring spot 72

Plum, damson, or bullace

Peach mosaic 27

Peach rosette 7

Prune dwarf 171

Ring spot . 72

Rosette mosaic 14

Western X-disease 46

Plum, domestica, or garden

Asteroid spot 84

Boron deficiency 244

Boron-excess injury 246

Copper deficiency 241

Iron chlorosis 230

Italian Prune leaf spot 210

Italian Prune sparse leaf 212

Line pattern 177

Little peach . 4

Manganese deficiency 235

Mild rusty mottle 116

Muir peach dwarf 64

Necrotic ring spot 164

Nitrogen deficiency 222

Peach mosaic 27

Peach yellows 1

Potassium deficiency 224

Prune diamond canker 175

Prune dwarf 171

Ring spot 72

Rosette mosaic 14

Sour cherry yellows 153

Standard prune constricting mosaic. . 18 5

Sweet cherry crinkle leaf 195

Tatter leaf 141

Zinc deficiency 237

Plum, flatwoods

Peach mosaic 27

Ring spot 72

Plum, hog

Peach mosaic 27

Plum, hortulan

Peach mosaic 27

Peach yellows 1

Phony 18

Plum hybrids

Line pattern 177

Little peach 4

Noninfectious plum shot hole 208

Peach rosette 7
276 HANDBOOK 10, U. S. DEPARTMENT OF AGRICULTURE

Page

Plum hybrids—Con.

Peach yellows 3

Prune dwarf . 171

Red suture , . . . 12

Rosette mosaic . 14

Western X-disease 46

Plum, Japanese

Asteroid spot 84

Boron-excess injury 246

Copper deficiency . . , ., 241

Golden-net 88

Iron chlorosis 230

Line pattern 177

Little peach 4

Manganese deficiency 235

Nitrogen deficiency 222

Peach mosaic 27

Peach rosette 7

Peach yellows . Í

Plum white spot 183

Prune dwarf Î71

Red suture H

Ring spot 71

Rosette mosaic 14

Sodium-excess injury 249

Tatter leaf 141

Zinc deficiency 237

plum, Mexican

Peach mosaic ...,,.. . 27

Phony ... 18

Plum, myrobalan

Line pattern 177

Page

Plum, myrobalan—Con.

Little peach 4

Muir peach dwarf 64

Necrotic ring spot 164

Peach mosaic 27

Peach yellows 1

Prune dwarf 171

Ring spot 72

Sour cherry yellows 153

Yellow bud mosaic Î3

Plum, pottawattamie

See wildgoose plum.

Plum, purple, or ornamental

Peach yellows 1

Plum, wildgoose

Little peach 4

Noninfectious plum shot hole 208

Peach mosaic 27

Peach yellows . 3

Ring spot 72

X-disease 3 8

Prune

See domestica plum.

Rose

Ring spot 72

Yellow bud mosaic 53

Tobacco

Peach rosette 7

Tomato

Peach rosette 7

X-disease . , 38

i^ U. S. GOVERNMENT PRINTING OFFICE: 1951—S91793