Market Diseases

Stone Fruits:

Cherries, Peaches,

Vectarines, Apricots,

and Plums

Agriculture Handbook No. 414

Ä.^NB^4^

Agricultural Research Service

UNITED STATES DEPARTMENT OF AGRICULTURE
Market Diseases

of

Stone Fruits:

Cherries, Peaches,

Nectarines, Apricots,

and Plums

By JOHN M. HARVEY, WILSON L. SMITH, JR.,

and JACOB KAUFMAN

Agricuhure Handbook No. 414

Agricuhural Research Service

UNITED STATES DEPARTMENT OF AGRICULTURE

Washington, D.C. Issued December 1972

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

Washington, D.C. 20402 - Price 65 cents

Stock number 0100-1419
Preface

This handbook is an extensive revision of and

supersedes Miscellaneous Publication No. 228,

Market Diseases of Fruits and Vegetables :

Peaches, Plums, Cherries, and Other Stone Fruits,

by Dean H. Rose, D. F. Fisher, Charles Brooks,

and C. 0. Bratley. This handbook is one of a series

designed to aid in the recognition and identification of market diseases, to provide information on

factors causing the diseases, and to present control

measures for reducing the economic losses caused

by these diseases during marketing.

The handbook is designed for use by market inspectors, research workers, shippers, receivers,

carriers, and others concerned with maintaining

the quality of fresh foods during marketing.

Other publications in this series are :

Agriculture Handbooks

28. Market Diseases of Tomatoes, Peppers, and Eggplants.

June 1952. (Revised February 1968.)

155. Market Diseases of Beets, Chicory, Endive, Escarole, Globe

Artichokes, Lettuce, Rhubarb, Spinach, and Sweetpotatoes.

April 1959. (Reprinted May 1967.)

184. Market Diseases of Cabbage, Cauliflower, Turnips, Cucumbers, Melons, and Related Crops. September 1961.

189. Market Diseases of Grapes and Other Small Fruits. November 1960. (Reprinted April 1966.)

303. Market Diseases of Asparagus, Onions, Beans, Peas, Carrots,

Celery, and Related Vegetables. September 1966.

376. Market Diseases of Apples, Pears, and Quinces. May 1971.

398. Market Diseases of Citrus and Other Subtropical Fruits.

(In press.)

Ill
PRECAUTIONS

Pesticides used improperly can be injurious to

man, animals, and plants. Follow the directions

and heed all precautions on the labels.

Store pesticides in original containers under

lock and key—out of the reach of children and

animals—^and away from food and feed.

Apply pesticides so that they do not endanger

humans, livestock, crops, beneficial insects, fish,

and wildlife. Do not apply pesticides when there

is danger of drift, when honey bees or other pollinating insects are visiting plants, or in ways that

may contaminate water or leave illegal residues.

Avoid prolonged inhalation of pesticide sprays

or dusts ; wear protective clothing and equipment

if specified on the container.

If your hands become contaminated with a pesticide, do not eat or drink until you have washed.

In case a pesticide is swallowed or gets in the

eyes, follow the first aid treatment given on the

label, and get prompt medical attention. If a

pesticide is spilled on your skin or clothing, remove clothing immediately and wash skin thoroughly.

Do not clean spray equipment or dump excess

spray material near ponds, streams, or wells.

Because it is difficult to remove all traces of herbicides from equipment, do not use the same equipment for insecticides or fungicides that you use

for herbicides.

Dispose of empty pesticide containers promptly.

Have them buried at a sanitary land-fill dump, or

crush and bury them in a level, isolated place.

NOTE: Some States have restrictions on the

use of certain pesticides. Check your State and

local regulations. Also, because registrations of

pesticides are under constant review by the U.S.

Department of Agriculture, consult your county

agricultural agent or State Extension specialist

to be sure the intended use is still registered.

IV
Contents

Page

Introduction 1

Parasitic diseases of stone fruits 2

Cherries 2

Alternaria rot 2

Black mold rot 3

Blue mold rot 4

Brown rot 5

Cladosporium rot 5

Coryneum blight 6

Gray mold rot 7

Rhizopus rot 8

Peaches, nectarines, and apricots 9

Alternaria rot 9

Anthracnose (bitter rot) 9

Bacterial spot 11

Black mold rot 12

Blue mold rot 13

Brown rot 14

Cladosporium rot 17

Coryneum blight 17

Diplodia rot 18

Gray mold rot 19

Leaf curl 20

Powdery mildew 21

Rhizopus rot 22

Ring pox 23

Rust 24

Scab 25

Sour rot 26

Plums 27

Alternaria rot (green mold rot) 27

Bacterial spot 28

Blue mold rot 28

Brown rot _ 29

Cladosporium rot 30

Coryneum blight 30

Gray mold rot 31

Rhizopus rot 32

Rust 32

Scab 33
Page

Noîiparasitic diseases of stone fruits 33

Orchard- and weather-related disorders 33

Cracking 33

Drought injury 35

Hail injury 35

Heat injury -—- - 36

Russeting 37

Split pits ^ 37

Storage-related disorders 38

Ammonia injury 38

Freezing injury 39

Internal breakdown 39

Shriveling 40

Sulfur dioxide injury . 42

Transit- and handling-related disorders 42

Bruising 42

Freezing injury 44

Shriveling 46

Sulfur dioxide injury 46

Insect injuries 46

Catface - 46

Fruit gumming 48

Thrip injury 49

Literature cited 50

General 50

Insect injuries 64

t.t. nrHiaim ei ««itcDuiiii

VI
MARKET DISEASES

OF STONE FRUITS

Cherries, Peaches, Nectarines,

Apricots, and Plums

By JOHN M. HARVEY, WILSON L. SMITH, JR., and JACOB KAUFMAN, research

plant pathologists, Market Quality Research Division,

Agricultural Research Service

INTRODUCTION

The market diseases of cherries (Prunus avium L.), peaches

(P. pérsica (L.) Batsch), nectarines (P. pérsica (L.) Batsch var.

nectarina (Ait.) Maxim.), apricots (P. armeniaca h.), plums (P.

salicina Lindl.), and prunes (P. domestica L.) are discussed in this

publication. The diseases are divided into two groups, the parasitic diseases and the nonparasitic diseases or disorders. Parasitic diseases are those caused by pathogenic organisms (fungi

and bacteria) and viruses. Nonparasitic diseases are those

caused by physical forces (bruising or freezing), physiological effects (internal breakdov^ns or shriveling), other nonpathogenic

factors, and by insects.

The parasitic diseases are further separated on the basis of host

fruit—diseases of cherries, diseases of peaches, nectarines, and

apricots, and diseases of plums (and prunes). Diseases of each

of these fruits, or groups of fruit, are arranged by causal factor.

Frequently a particular organism will cause disease in more than

one host. In such cases, the symptoms of the disease are given

for each host, but details about the causal organism and control

are given only for the host on which the disease is most common

or of greatest economic importance. Cross-references are provided, which enable the reader to obtain additional information

about the cause and control of the disease.

In this handbook, nonparasitic diseases are separated into three

groups—diseases that are orchard and weather related, those that

are storage related, and those that are transit and handling related. The causes of nonparasitic disorders cannot always be

clearly defined, so that these disorders are arranged primarily on

the basis of symptom expression (cracking, russeting, shriveling).
2 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

Each disease is considered in respect to its geographical distribution, where it occurs in marketing channels, its economic importance, varietal susceptibility or resistance, external and internal symptom expression, causal factors, temperature relations,

and control measures. For parasitic diseases, consideration also

is given to the mode of infection, where and when it takes place,

predisposing factors to infection, dissemination of the disease, and

how it may be related to other disorders (bruising).

Control of market diseases or prevention of disorders is considered prim.arily in relation to postharvest handling, storing,

and shipping practices. Orchard treatments vary with the locality, and instruction on such control measures should be obtained

from farm advisors or county agents serving the pertinent production area. Available information is given on control or reduction of disease losses by proper refrigeration practices, controlled

atmospheres, fungicide treatments, heat treatments, or packaging.

Injurious insects sometimes cause disorders of stone fruits that

resemble certain parasitic diseases or orchard-related nonparasitic

disorders. Insect injuries that may be confused with these market diseases are described; injuries that obviously are the direct

result of boring or chewing insects are not included in this handbook.

PARASITIC DISEASES OF STONE FRUITS

Cherries

Alternaría Rot

Alternaría sp.

Occurrence and symptoms

Alternaria rot is a common market disease of the principal

varieties of sweet cherries grown in California and the Northwest

and of sour cherries grown in Michigan.

Alternaria rot of cherries is dark brown to black, firm, and

slightly moist. The affected area appears as a spot on the surface

of the fruit and may be covered with olive-green spores and white

strands of mold. The rotted tissue beneath the spot is cone

shaped, with the apex of the cone extended toward the pit. The

cone separates readily from the surrounding tissue and can be

lifted out.

The symptoms of alternaria rot are similar to those of ciado-
MARKET DISEASES OF STONE FRUITS 3

sporium rot, but in the former the surface mold is darker, the

decayed tissue more moist and dark, and the enlargement of the

lesions more rapid (pi. 1, A).

Causal factors

The fungus, Alternaría, is widespread in nature, growing on

dead leaves, twigs, and other material in the orchard. The spores

are windborne and on germination, the fungus enters the cherry

through breaks in the skin caused by cracking in the orchard or

wounding during picking and packing.

Most species of Alternaría causing fruit rot grow best at about

77° F. and grow very slowly at 32° F.

Control measures

Since the fungus is less active at low than at moderate or high

temperatures, cherries should be precooled as soon after harvest

as possible and stored or transported as close as possible to the

recommended holding temperature of 31° to 32° F. Careful handling to prevent bruising or wounding during picking, packing,

and loading would make the fruit less subject to infection.

Decay in stored cherries also has been reduced by modified atmospheres in which the carbon dioxide (CO2) level is held at 10

percent. Packing the fruit in boxes with polyethylene liners has

been effective in maintaining a high CO2 level in atmospheres in

transit and marketing.

(See 72, 73, 1ÍU, 162, 186.)^

Black Mold Rot

Aspergilliis niger v. Tiegh.

Black mold rot of cherries is rarely found on the market. Rot

caused by this mold is watery and mushy and can be scooped out,

leaving a clean cavity in the surrounding flesh. The surface of

the affected area becomes cracked and small white tufts of mold

appear. As spores are produced, the mold turns jet black.

Aspergillus niger grows best at 86° to 98° F. and grows very

little at temperatures below 45°. The disease, therefore, is of

little consequence when cherries are properly refrigerated.

See Peaches, Nectarines, and Apricots, page 12.

{Seei<50, 186.)

' Italic numbers in parentheses refer to Literature Cited, p. 50.
4 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

Blue Mold Rot

Pencilliiim expansum Lk. ex Thom,

Occurrence and symptom§

Blue mold rot is one of the most important disorders of cherries

on the market. It is particularly prevalent in fruit that has been

exposed to rainfall or high moisture conditions in the orchard.

Such conditions may cause cracking of the skin, which predisposes

the fruit to infection. The Bing and Tartarian varieties are particularly susceptible to cracking ; Lambert is less susceptible. Gen=

erally, large-fruited varieties tend to crack more readily than smallfruited varieties and susceptibility to cracking increases as the

fruit matures.

Externally, blue mold rot first appears as a circular, ñat, lightbrown area. Internally, the affected tissue is very soft and watery. As the rot develops, the skin covering it cracks readily and

small, white tufts of the mold appear. Under humid conditions,

the mold grows over the surface of the rotted area and soon produces a crop of bluish-green spores. In the late stages of decay,

affected cherries become crushed during handling and the decayed

tissues contaminate surrounding fruit (pL 1, B),

Causal factors

Blue mold rot is caused primarily by the fungus, Penicillmm

expansum, although some other species of Penicillmm may be associated with the disease. This fungus produces a large number of

spores, which are widely disseminated in the air. Penicillmm

seldom infects the fruit through the intact skin, but enters through

cracks caused by moisture or injuries during harvesting and packing. Susceptibility increases as the fruit matures.

Penicillmm expansum grows best at about 77"" F. and growth

almost ceases at 32°. The spores germinate readily at 77°, but

germination is greatly delayed (7 to 14 days) at 32°.

Control measures

Since growth of the causal fungus is greatly reduced at low temperature, rapid precooling and storage at 81° to 32° F. are effective

in reducing losses from blue mold rot. Temperatures in transit

should be maintained as close to 32° as possible.

High CO2 levels in atmospheres also reduce the development of

blue mold rot in cherries. A 20-percent level of CO2 at 36° or 45°

F. has been found to have about the same inhibitory effect on the
MARKET DISEASES OF STONE FRUITS O

development of blue mold rot as a temperature of 31'' without

CO2. High CO2 levels in atmospheres can be achieved in transit by

using polyethylene liners in the boxes in which cherries are packed

or by adding 800 to 1,000 pounds of dry ice to the refrigerator car

used to transport the fruit.

Preventing skin punctures or bruising during harvesting and

handling will reduce infection ports for blue mold.

(See 63, 70, 72, 73, lUy 152, 186, 187, 193,211.)

Brown Rot

Monilinia fructicola (Wint.) Honey and M. laxa

(Aderh. & Ruhl.) Honey

Occurrence and symptoms

Brown rot is an important disease of cherries, particularly in

humid or wet seasons when it may affect up to one-third of the

crop. The disease is found on cherries grown in California, the

Northwest, and in other areas of the United States. Brown rot

affects fruit in the orchard and during transit and marketing.

The rot is light brown at first, but darkens later. The margins

of the affected area fade into the normal fruit color, leaving no

distinct line separating decayed from healthy tissue. The skin

covering the rot remains firmly attached to the tissue beneath.

Brownish-gray masses of spores are produced quickly on the surface of decayed portions of the fruit. At room temperature, the

decay spreads rapidly over the affected fruit and to adjacent fruits

(pLl,C).

Causal factors and control measures

See Peaches, Nectarines, and Apricots, pages 15 and 16.

(See 25, 82, 3i, 65, 125, 202, 211.)

Cladosporium Rot

Cladosporium herharum Lk. ex Fr.

Occurrence and symptoms

Cladosporium rot causes serious losses in sweet cherries during

seasons in which weather conditions cause cracking of the skin.

Cherries from California and the Pacific Northwest are frequently

affected.

The decayed area is usually small, often affecting only the lining
6 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

of the erack or wound around which it centers. The decayed tissue

is hard, dry, gray to black, and cone shaped with its apex extending

deep into the fruit. This cone can be easily removed from the

surrounding healthy tissue. External signs of the fungus are a

thin, fluffy growth of white mold that covers the decayed area

and that produces abundant yellowish-olive spores (pi 1, D).

Caudal factors

Cladosporimn herbarum, the causal fungus, is widespread in

nature, growing and sporulating abundantly on dead plant materials. Decay caused by the fungus develops most rapidly at about

72° F., but also develops slowly at storage temperatures as low as

34'', Other organisms frequently gain entrance through the same

wounds and mask the primary symptoms of cladosporium rot.

Control measures

An important control measure for this disease is the prevention

of wounds, because the causal fungus enters the fruit only through

breaks in the skin. Careful sorting to remove cracked fruit at the

packinghouse and rapid cooling will reduce the incidence and

development of decay. Maximum refrigeration should be maintained in transit to provide temperatures as close to 32° F. as

possible.

(See^5, i<50.)

Coryneum Blight

Coryneum carpophiliini (Lev. ) Jauch,

Occurrence and symptoms

Coryneum blight is primarily a disease of cherries and other

stone fruits grown in the Western United States and is rarely

found in the East. The disease is most evident on the leaves

where it causes spots or ''shothole," but the organism also attacks

the fruit, causing small dry spots. The flesh below these spots is

affected with rot that gradually extends to the pit or may spread

over the whole fruit.

Causal factors and control measures

See Peaches, Nectarines, and Apricots, page 18.

(See 83, 87, 136, 160, 203, 20i.)
MARKET DISEASES OF STONE FRUITS 7

Gray Mold Rot

Botrytis cinérea Pers. ex Fr.

Occurrence

Gray mold rot is frequently found on cherries from all producing

areas in the United States. Inspection records over a period of

several years have shown that an average of almost 0.5 percent of

the cherries arriving at eastern markets have had gray mold rot.

The disease is much more prevalent in years when cool, moist

weather occurs shortly before harvest.

Symptoms

Gray mold rot first appears as a light-brown spot on the skin.

The spot later becomes covered with a delicate growth of Botrytis

cinérea, the causal fungus, and the underlying tissue becomes

somewhat watery and a darker brown. As the decayed area

enlarges, the fungus growth becomes more prominent. Under

relatively dry conditions, gray spores are produced abundantly

over the decayed areas of the fruit; under moist conditions, as in

a box of cherries with a film liner, an abundant white growth of

fungus may cover the affected fruits and spread to adjacent ones.

The skin near the margins of decayed areas slips easily under

pressure from the finger, as in rhizopus rot, but the decayed tissue

does not have the sour odor characteristic of rhizopus rot—gray

mold has no definite odor. Spread of the fungus by contact from

infected to sound fruits often occurs, resulting in nests of molded

fruit in a box (pi. 1, E),

Causal factors

Gray mold rot is caused by the fungus, Botrytis cinérea, which

causes decay in many different fruits, vegetables, and other crops.

This fungus may enter the fruit through breaks in the skin or may

penetrate the skin after growing on dead flower parts or other

plant debris adhering to the surface of the fruit.

Botrytis cinérea grows best at 72" to 77'' F. and fruit rot develops rapidly at these temperatures. Slight growth occurs at 32''

and decay may increase slowly even at this low temperature. A

50-percent reduction in growth of Botrytis occurs when 20 percent

COo is added to the atmosphere, and spore germination is completely inhibited in atmospheres with a CO2 level of 32 percent.
8 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

Control measures

Careful handling during picking and packing and elimination of

culls and rotted fruit are eifective methods of reducing market

losses from gray mold. A comparison of cherries handled commercially and those especially handled to prevent bruising showed

that almost four times as much gray mold rot developed in the

commercially handled fruit.

Prompt precooling after harvest greatly reduces the development of gray mold. Atmospheres with a CO2 level of 10 percent

have been found to reduce decay and extend storage life. Film

liners are effective in retaining CO2 during transit or dry ice may

be used to build up the CO2 level in the atmospheres. Certain

postharvest fungicidal dips have been found effective in reducing

gray mold rot.

( See 78, 162, 200, 202, 211,212,)

Rliizopus Rot

Rhizopus stolonifer (Ehr. ex Fr.) VuilL

Occurrence

Rhizopus rot is one of the most important postharvest diseases

of cherries. A survey indicated that an average of 0.7 percent

of the cherries reaching the New York market were affected by

this disease. The incidence of rhizopus rot increases as the fruit

ripens; cracks or bruises in the skin also favor the disease.

Symptoms

Rhizopus rot first appears as water-soaked, tender, slightly darkened areas on the fruit. Later the entire fruit breaks down, producing a red, loose mass of rotted tissue covered with an abundant

coarse growth of the fungus. Dull, black fruiting bodies of the

fungus are produced over the surface. The mold quickly spreads

over large parts of a box of fruit and may involve the entire contents. Watery, red juice may drip from such cherry boxes (pL 1,

F).

Causal factors

See Peaches, Nectarines, and Apricots, page 23.

Control measures

Since Rhizopus stolonifer is a **high temperature'' organism,

it is best controlled by cooling the fruit promptly and holding it at
MARKET DISEASES OF STONE FRUITS 9

low temperature in transit or in storage. The causal organism

ceases to grow at temperatures below 45° F. Maximum refrigeration is recommended in transit, with temperatures as near 32° as

possible.

Controlled or modified atmospheres also have been efliective in

reducing rhizopus rot. Spore germination is completely inhibited

in atmospheres with 8 percent CO2 and vegetative growth of the

mold is reduced by one-half in those with 20 percent CO2. Atmospheres with 10 percent CO2 have reduced decay of cherries in

storage tests. Atmospheres with high levels of CO2 can be obtained in transit by using polyethylene box liners or by using dry

ice in refrigerated railcars or trailers. From 800 to 1,.000 pounds

of wrapped dry ice can be placed in a crib above the brace of a

car, with an additional 200 pounds broken up in the ice bunkers of

the car. In trucks the wrapped dry ice is suspended well above

the load to prevent freezing.

(See 70, 71, 72, 73, Ul, 152,162, 200,)

Peaches, Nectarines, and Apricots

Alternarla Rot

Alternaría sp.

Occurrence and symptoms

Alternarla rot may occur on peaches, nectarines, and apricots

when these fruits are stored for long periods at low temperature.

The disease is rarely found on freshly harvested fruit.

Alternarla rot is black to greenish black, firm, slightly sunken,

and moist, and usually affects only the surface of the fruits. In

advanced stages, the affected areas may be covered with olivegreen spores of the fungus and the rot may extend deeper into the

flesh, forming a cone that can easily be scooped out (pi. 2, A ; pi.

Causal factors and control measures

See Cherries, page 3, and Plums, page 27.

Anthracnose (Bitter Rot)

Glomerella cingulata (Ston.) Spauld. & Schrenk,

Occurrence

Anthracnose has been an important disease of peaches in Japan

since 1920. It was first observed in the United States in ship-
10 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

ments of peaches from Georgia in 1947. In succeeding years, the

disease became serious in most Southeastern peach-growing States

and later was reported on peaches grown in most States on the east

coast and in the Midwest. The disease caused serious losses from

1947 to about 1955, but since that time has become less important.

Peaches infected with anthracnose are usually detected when the

fruit is harvested and diseased fruit is discarded during packinghouse operations. However, some incipient infections escape detection and cause losses during marketing.

Symptonis

The first symptoms of anthracnose on peach fruit are one or

more small, circular, brown spots, % to 14 inch in diameter.

These spots occur indiscriminately over the surface of the fruit

and closely resemble the early stages of brown rot. In the early

stages, the spots may be slightly moist, but usually they are firm

and dry. The spots slowly enlarge to about 1 inch in diameter

and the tissue beneath collapses, causing a depression to form

in the center. In advanced stages, the depressed area may extend

Vn to 14 inch into the ñesh. The affected area is surrounded by a

firm, circular margin. A fine, grayish growth of the fungus may

cover the spots and later concentrie rings of salmon-pink spore

masses are produced in the depression. In severe infections, the

spots may coalesce and cover a large part of the fruit (pi. 4, G).

Causal factors

The causal ínnguñ, Glomerella cmgiilata, m the same organism

that causes bitter rot of apples. The fungus overwinters in blue

lupine in the Southern States and infects peaches in the early

stages of growth in the spring. Infections also may occur in later

stages of growth and damage from the disease becomes apparent

as the fruit approaches maturity. Two strains of the organism

exist, one having a pink and the other a gray vegetative growth.

The pink strain grows more rapidly and causes decay to develop

faster than the gray strain at temperatures below 50° F. No

growth occurs with either strain at temperatures below 40° or

above 95°. The optimum temperature for growth of both strains

is 80°.

Control measures

Since the symptoms of anthracnose are often apparent when

peaches arrive at packing sheds, careful grading will eliminate

most diseased fruit from the market. Storage and transit tern-
MARKET DISEASES OF STONE FRUITS 11

peratures near or below 40° F. will prevent further development

of the decay. In regions where the blue lupine is used as a winter

cover crop, the elimination of this host has done much to reduce

losses and to minimize the importance of anthracnose as a market

disease.

{See 61, 138, 1^9, 178, 197.)

Bacterial Spot

Xanthomonas pruni (E. F. Sin.) Dows.

Occurrence

Bacterial spot is a serious disease of peaches, nectarines, and

apricots. Commercially it is most important as a disease of

peaches, causing losses in the eastern and mid-western parts of the

United States, but not in fruit-growing sections west of the Rocky

Mountains. The disease also occurs in Australia, Brazil, Canada,

Japan, New Zealand, and Russia. Most varieties of peach are

susceptible to bacterial spot, particularly Sun High and late-maturing varieties Elberta or J. H. Hale. Losses from bacterial spot

are reflected not only in damaged fruit, but also in reduced yields

resulting from defoliation of trees affected with the disease.

Symptoms

Bacterial spot appears as circular, faint, brown spots about 0.5

to 1.0 mm. in diameter on maturing peach fruits in the orchard.

As the spots enlarge, the centers darken slightly and become

sunken ; the margins of the spots have a watersoaked appearance.

Spots may occur on any area of fruit, thus differing from scab,

which occurs mostly at the stem end. The spots sometimes coalesce and cover large areas. Numerous types of skin cracking

may occur. Fruits infected at an early stage of development

usually are more malformed than those infected later. Cracks

in the fruit range from very small and shallow cracks with a

greenish halo to deep, open cracks containing a yellowish, gummy

exúdate. This exúdate also may be produced in large spots and

often dries into hornlike projections (pi. 5, A and B).

Causal factors

Xanthomonas pruni overwinters in infected twigs and in the

spring is spread mainly by wind and rain to leaves and fruits.

The bacterium infects blossoms or the unbroken skin of the fruit.

It grows luxuriantly at temperatures between 75"" and 83° F. and

may cause severe infection in the orchard between 70° and 85°.
12 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

Growth of the organism is reduced above 85° and the bacterium

ceases to multiply at 100°. It is killed in 10 minutes when exposed

to a 124° temperature. Fruit on weak trees are more susceptible

to attacks by X, pruni than fruit on vigorous trees.

Control measures

Since bacterial spot is primarily an orchard disease, affected

fruit should be graded out in the packinghouse. Postharvest

treatments do not reduce the disease. Control measures in the

orchard include proper chemical spray applications and good cultural practices necessary to produce vigorous trees,

(See 7, 8, 56, 58, 92, 102, 110, 118,121, 159,)

Black Mold Rot

Aspergillus niger v. Tiegli.

Occurrence

Black mold rot of peach, nectarines, and apricots occurs occasionally on all varieties of these fruits, but never causes serious

losses. Most commonly it attacks fruit during warm ripening

periods following prolonged storage or transit. Black mold rarely

occurs on freshly harvested fruit.

Symptoms

Early symptoms of black mold rot on peaches are small, tan,

slightly sunken spots at various places on the fruit. As the spots

enlarge, the tan skin becomes wrinkled in concentric circles.

Later a scant, white growth of mold appears near the center of

the spot and then spreads over the affected area. The mold produces abundant spores that are yellow at first, but soon turn black,

giving the rot a sooty appearance. Sometimes the sooty area is

surrounded by a scant, white growth of mold and tan discolored

skin. The flesh % to 14 inch beneath the affected area turns

brown and mushy and can be scooped out, leaving a saucerlike

hollow surrounded by healthy tissue (pi. 4, A and S).

Causal factors

The causal fungus, AspergiUus niger, is widespread in nature,

growing on organic matter in the orchard and elsewhere. It can

contaminate peaches or other stone fruits during harvesting and

packing. A. riiger grows most rapidly at high temperatures, the

optimum being between 86'' and 98'^ F. Little or no growth

occurs below 45° or above 113°. Spores will be killed at 131° for
MARKET DISEASES OF STONE FRUITS 13

30 minutes. Normally the organism does not attack uninjured,

freshly harvested peaches unless they are overripe. Losses from

black rot usually occur on injured fruit or fruit subjected to prolonged storage at low temperature before ripening at high temperature.

Control measures

Losses from black mold rot can be reduced by careful handling

to avoid injury to the fruit, avoiding excessive long storage periods,

and using sanitary measures in packinghouses and in v^holesale

and retail markets.

(See 160, 186.)

Blue Mold Rot

Pencillium sp.

Occurrence and symptoms

Blue mold rot usually does not occur on freshly harvested, uninjured peaches, nectarines, or apricots. The rot commonly is found,

however, on injured or overripe fruit or fruit that has been stored

at low temperatures for long periods.

The first symptoms of blue mold rot on these fruit are small tan

spots occurring anywhere on the surface. The skin over the spots

is moist and readily breaks or slips from the fruit. Beneath the

spot the flesh is tan and moist, but fairly firm. With slight pressure, the infected tissue can be scooped out, leaving a saucerlike

depression up to ^4. to 1/2 inch deep and surrounded by healthy

tissue. As the spot enlarges, white tufted cushions of mold appear

near the center, which later produce masses of powdery, bluegreen spores. The sporulating areas often are surrounded by a

white vegetative growth of the fungus. The affected areas gradually enlarge, but rarely involve the whole fruit (pi. 3, E and F).

Causal factors

See Cherries, page 4.

Control measures

See Cherries, page 4.

Peaches and nectarines are not as tolerant of atmospheres with

high CO2 levels as cherries, nor are they as subject to blue mold rot

as cherries. Consequently, atmospheres with high CO2 levels generally are not used in commercial shipments of peaches and nectarines. Controlled atmosphere storage of these fruit at 32'^ P. v^ith
14 AGRICULTURE HANDBOOK 414, U.S. ÜEPT. OP AGRICULTURE

1 percent oygen and 5 percent CO2 has reduced physiological disorders greatly, but has reduced decay only slightly.

(See 10, 160/186,)

Brown Rot

Monilinia fructicola (Wint,) Honey and M.laxa

(Aderh. &Ruhl.) Honey

Occurrence

Throughout the world brown rot is the most important disease

of peaches, nectarines, and apricots. In the United States the

disease occurs wherever these fruits are grown, but consistently

causes the greatest losses to peaches grown in the Southeast.

Brown rot develops on peaches in the orchard, in packinghouses,

during transit, during marketing, and in the homes of consumers.

The rot develops on freshly picked fruit, as well as on fruit after

long transit or storage periods. It will develop on relatively

immature fruit nearly as fast as on mature fruit. No commercial

varieties of peaches, nectarines, or apricots are resistant to this

disease. The J. H. Hale and Red Top peach and most nectarines

are particularly susceptible to brown rot. Most canning cling

peaches and early soft flesh peaches are highly susceptible.

The development of brown rot during marketing of these fruits

is correlated closely with weather conditions at the time of harvest.

Rainy periods stimulate spore production on infected twigs or

mummies, and if fruit is maturing during this period, infection in

the orchard may be severe. When high humidity follows rainy

periods, spore production continues for long periods. In dry

periods, even though the relative humidity may be high, spore

production is limited and late-season infection in the orchard is

slight.

Symptoms

The earliest symptoms of brown rot are small, water-soaked

spots on the surface of fruits. Beneath these spots, the flesh also

is water soaked to glassy, the discoloration extending about Va

inch. Within 24 hours, the skin and affected flesh become brown

to black. At 60° to 80° F. these spots enlarge rapidly, usually

remain circular and nonsunken, and are covered with a tough,

leathery skin that, even with moderate pressure, remains intact

over the decayed flesh. The flesh becomes brown and somewhat

watery, but firm, the decay often extending to the pit of the fruit.
MARKET DISEASES OF STONE FRUITS 15

In advanced stages, tan-gray, powdery spore masses, often in concentric rings, cover the surface of affected areas. Within 3 to 4

days at room temperature, the entire fruit may be decayed, but

with the skin remaining intact. Later these fruit shrivel and

become mummies.

Brown rot spreads rapidly from diseased to healthy fruit in shipping containers. Severe ''nesting'' usually occurs when heavily

infected fruits are packed and held at moderate temperatures (pi.

2, C and D; pL 6, A, J?, and C).

Causal factors

Two species of Monilinia, M, fructicola and M, laxa, produce

brown rot of stone fruits. In the United States, M. laxa is found

mainly in California, whereas M. fructicola is found throughout

the country.

These fungi overwinter chiefly on mummies that remain on

trees or that have fallen to the ground. Sometimes the brown rot

fungi overwinter on twig and limb cankers. During rainy periods

in the spring, spores are disseminated from these sources and infect peach blossoms, causing additional twig infections. Young

fruits may become infected by spores from these twigs ; the infection may remain, latent until the fruits mature. Additional infections may occur during rainy periods later in the season when

the fruits are maturing. The brown rot organism can penetrate

the unbroken skin of the fruits, but insect injuries, hail injury,

wind whipping, and bruising greatly increase infection.

Fruits also may become infected in packinghouses or markets

when in contact with contaminated belts, tables, or boxes. Hydrocoolers, in almost universal use in the Eastern and Southeastern

United States, can be one of the principal methods of spreading

brown rot. If the water in these coolers is not changed frequently

or treated with a fungicide, a large population of Monilinia spores

may contaminate the water and infect fruit passing through the

cooler.

Spores of M. fructicola can germinate and grow at temperatures

from 32° to 90° F. For rapid growth of this organism and for

spore production, temperatures from 60° to 80° are ideal. Most of

the spores are killed when exposed to 120° water for 3 minutes or

to 125° water for 1 minute. Exposure to 130° air with 90-percent

relative humidity for 1 hour also killed the spores, but exposure

to air with only 50-percent relative humidity did not kill the spores.

Dipping fruit in 125° water for 2 to 3 minutes has eiïectively

killed spores on the surface.
16 AGRICULTURE HANDBOOK 414, U.S. DEPT. OP AGRICULTURE

Germination of Monilinia spores requires the presence of free

water. Rainy periods, therefore, will result in severe orchard

infections, especially when fruit are nearly mature. High humidity following the rainy period will prolong the infection period.

However, high humidity alone does not provide sufficient moisture

to seriously increase the development and spread of this decay.

Control measures

Primary control of brown rot should begin with sanitation practices in the orchard, in the packinghouse, and on the market. Destroying or burying mummified fruits in the orchard, cleaning

grading and packing equipment, keeping the water clean in hydrocoolers, and destroying cull piles of fruit around orchards and

packinghouses will reduce the population of brown rot spores and

hence reduce the possibility of fruit infection. Control measures

also should include applying insecticides for flies and gnats at

packinghouses and markets since these insects carry Monilinia

spores from diseased to healthy fruit.

Proper orchard spray schedules are necessary to control brown

rot in orchards. For details, the U.S. Department of Agriculture

or State agricultural colleges should be consulted.

Refrigeration is the most commonly used method of controlling

brown rot after harvest. Temperature studies have shown that as

much brown rot develops in peaches held 1 day at 75° F. as in 3

days at 50°, 7 days at 41°, or 25 days at 32°. Prompt cooling of

fruit to temperatures below 40° will reduce the growth and spread

of this organism. Hydrocooling is a rapid method of removing

field heat. Maintaining transit temperatures below 40° will slow

the development of brown rot, though further development will

occur when fruit is moved to moderate marketing temperatures.

Postharvest fungicide treatments, such as chlorine in the hydrocooling water, have been eifective in reducing populations of Monilinia spores on the surface of peaches, but have not controlled the

growth of organisms that have already infected fruit in the

orchard. Heat treatments have been eifective in controlling incipient infections of peaches and nectarines. Dipping the fruit

in 125° to 128° F. water for 2 to 21/2 minutes destroys Monilinia

spores on the fruit and also prevents the development of organisms

already established under the skin.

(See 8, 9; 11, 12, 22, 29, SO, SI, S3, 46, Â7, Â8, 59, 76, 8S, 89, 90,

91, 98,99,100, IOS, 115,120, 127, 130,132,139,156, 157, 158, 161,

166, 170, 176, 177, 180,196, 202, 205.)
MARKET DISEASES OF STONE FRUITS 17

Cladosporium Rot

Cladosporium herbarum Lk. ex Fr.

Occurrence and symptoms

Cladosporium rot rarely occurs on peaches, nectarines, or apricots. Fruits subject to long storage or transit periods sometimes

suffer from this disease.

Cladosporium rot usually affects only a small area of the fruit,

such as the tissue lining a wound or skin break. A thin, fluffy,

white growth of mold usually covers the affected area. In late

stages the surface of the decay turns yellowish olive as spores of

the fungus are produced. On peaches the spots usually are less

than 1 inch in diameter. The most striking feature of the decay is

a hard, cone-shaped, gray to black core extending deep into the

flesh. The core is surrounded by moist, brown tissue from which

it is easily separated.

Causal factors and control measures

See Cherries, page 6.

(See 160,)

Coryneum Blight

Coryneum carpophilum (Lev.) Jauch.

Occurrence

Coryneum blight was first recorded in France in 1853 and occurs

on peaches, nectarines, and apricots in most countries of Europe,

in Algeria, in Australia, and in New Zealand. In the United

States, the disease is most serious in the Pacific Northwest, but

also causes damage to stone fruits grown in California, Colorado,

Indiana, Michigan, New York, Ohio, and Utah. Coryneum blight

also is known as peach blight, winter blight, pustular spot, and

shot hole. The disease primarily affects twigs, dormant buds,

leaves, and blossoms on peaches and nectarines, but sometimes

damages the fruit. On apricots, the disease more frequently

attacks the fruit. Diseased fruits are usually culled in the packinghouse, but occasionally reach the market.

Symptoms

On the fruit, coryneum blight causes small, purplish-red, circular spots that usually are distinct from one another. The spots

may enlarge to Vg or 14 i^i^h in diameter, a cream-colored area

develops in the center, and the margins become dark red to brown.
18 AGRICULTURE HANDBOOK 414, U.S. DEPT, OF AGRICULTURE

Later the spots are slightly sunken and colored rusty brown.

Small cracks sometimes develop in affected areas, and gumming

occurs (pi. 2, B; pi. 4, E and F).

Causal factors

The causal fungus, Cornyneum carpophihim, infects buds and

twigs during moist weather in the fall and winter. Blossoms and

young fruit may become infected during the warm, rainy spring

weather. The spores are dispersed by rain or splashing water.

Infection occurs when susceptible parts of the hosts are wet for

several hours. The optimum temperature for decay development

and growth of the fungus is near 70° F. Decay development is

somewhat slower at 80° than 70°, and at 40° decay development is

delayed for 15 to 20 days. Spores of the fungus can germinate at

40° and incipient infections may occur. Decay resulting from

these infections develops very rapidly when fruits are transferred

to higher temperatures.

Coryneum blight does not spread from diseased to sound fruit

after harvest, although there is some indication that individual

spots may enlarge. Spots 1/2 inch or more in diameter and sunken

Vs to 14 inch below the margins have been observed on the market.

Such spots are considerably larger than those commonly found at

harvest.

Control measures

Control of coryneum blight depends upon proper applications

of chemical sprays in the orchard. After harvest, decay development may be delayed by storing and shipping the fruits at temperatures below 40° F.

(See 40, 62, 83, 87,136,160,173,17U, 203,20i, 209.)

Diplodia Rot

Diplodia natalensis P. Evans

Occurrence

Diplodia rot first was observed on peaches in Georgia in 1950.

The disease has been found since on peaches grown in several other

States on the east coast. Diplodia rot is found most commonly

on mature-ripe fruit, but also may develop during ripening of previously stored green fruit. Although the rot Is not of great economic importance, the potential loss is important since diplodia

rot develops rapidly at the temperatures at which peaches normally are ripened.
MARKET DISEASES OP STONE FRUITS 19

Symptoms

In its early stages, diplodia rot may be mistaken for either

brown rot or rhizopus rot. The small, light-brown spots caused

by Diplodia enlarge rapidly at moderate temperatures and may

cover most of the peach. The skin over affected areas is somewhat softer than that of peaches with brown rot, but more tenacious than that of fruit with rhizopus rot. The decayed flesh is

tan to brown, is somewhat watery, and sometimes has a sour odor.

The decay gradually extends to the pit and eventually causes the

whole fruit to shrivel or mummify. Surface growth of the mold

over affected areas is profuse, fine, and cottony white. Later,

gray to black fruiting bodies appear over the surface of fruit in

advanced stages of decay (pi. 4, C).

Causal factors

Rot caused by Diplodia natalensis develops after fruits are harvested and is more prevalent on mature ripe than on immature

green peaches. The initial infection may occur at an injury, but

the decay will spread by contact from decayed to sound fruit, sometimes involving all the fruit in a box. On mature fruit the decay

develops most rapidly at 80° to 90° F. and at high relative humidity. The maximum temperature for growth of the causal fungus

is 102° and the minimum is 45° and 50°.

Similar diseases of peach caused by Diplodina pérsicas (Home

and Hawthorne) and Phomopsis persicae (Sacc.) Smith and Ramsey have been reported from Louisiana and South Carolina.

Control measures

Specific control measures have not been developed for this

disease, but obvious ones would include refrigeration below 45° F.,

careful handling to reduce injuries, packinghouse sanitation, and

restricting the length of the storage period for fruit from orchards

known to harbor the Diplodia fungus.

(See 9i, 95,171, 172, 207, 208,)

Gray Mold Rot

Botrytis cinérea Pers. ex Fr.

Occurrence and symptoms

Gray mold rot rarely occurs on freshly harvested and marketed

peaches, nectarines, or apricots, but does occur on these fruits if

storage or transit periods have been excessively long. Fruits that
20 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

have been injured are subject to gray mold rot earlier in the postharvest period.

The first symptoms of gray mold are light-colored spots that may

occur anywhere on the fruit. The surface of the spot turns tan,

becomes slightly wrinkled, and is a lighter tan near the margins.

The skin over the decayed area slips readily from the underlying

tissue when a slight pressure is applied. As the spot enlarges, a

white to gray growth of the mold appears. Later large numbers

of gray-brown spores are produced. The decayed flesh is brown,

soft to mushy, and watery (pi. 2, E and F ; pi. 3, A, B, and C).

Causal factors and control measures

See Cherries, pages 7 and 8.

(See 160,)

Leaf Curl

Taphrina deformans (Berk.) Tul.

Occurrence

Leaf curl occurs wherever peaches and nectarines are grown,

even though it is easily controlled by proper orchard treatments.

Apricots are immune to leaf curl. On peaches and nectarines the

disease originates in the orchard where the leaves may be severely

damaged, often resulting in almost complete defoliation of the

trees and great reductions in yield. Sometimes the fruits are

affected, but these usually are culled at the packinghouse and seldom reach the market. In some peach-growing areas losses may

range up to 15 percent of the crop in addition to indirect losses

caused by defoliation.

Symptoms

Symptoms of leaf curl on fruits are red blotches that may occur

anywhere on the surface. Sometimes depressed, reddish, lacy

markings occur on the skin. Large, partly red, wartlike protuberances may develop in the red blotches, or overgrowths occur,

causing the fruits to be misshapen. In severely affected fruit,

deep cracks may develop.

Causal factors

Spores of Taphrina defo7^7nans, the fungus causing leaf curl,

survive during the summer, fall, and winter on the surface of tree

branches or on the ground. In the spring, the spores germinate

and infect young leaf and flower buds. When young fruit become
MARKET DISEASES OF STONE FRUITS 21

infected, they usually fall from the tree. Maturing fruit may be

attacked when proper weather conditions exist. The organism

can grow at temperatures below 50° F. and up to about 86°, but

optimum growth is at 68°. The actively growing fungus is killed

at 115°, but when dried or dormant, it will withstand temperatures

up to 203°. The disease is favored by cold, wet, spring weather

and usually is of minor importance in drier areas of the Western

United States.

Control measures

Control of leaf curl depends on spraying with a fungicide before

any vulnerable tissue is exposed in the spring. One application of

a suitable fungicide at the correct time is all that is necessary.

(See 8, 83, 87,104,126,128,129,1Í0,160,186,)

Powdery Mildew

Sphaerotheca pannosa (Wallr. ex Fr.) Lev. var.

persicae Woron.

Occurrence

Powdery mildew occurs on peaches, nectarines, and apricots,

affecting primarily leaves and fruit in the orchard. The disease

is widespread over most areas where these fruit are produced.

The Rio Oso Gem peach variety is particularly susceptible to powdery mildew. In California, powdery mildew of apricots has been

correlated with the distance of the orchards from infected rose

plantings. The disease is relatively unimportant as a marketing

disease because most affected fruit is discarded at the packinghouse, but serious losses sometimes occur when marred fruit may

be rejected both for fresh market and for canning.

Symptoms

Symptoms of powdery mildew on apricot fruit first appear in

late spring or early summer when the fruits are small and green.

Light-green spots covered with a whitish growth of mold may

occur over much of the fruit surface. As the fruit develops, it

may become flattened on the affected side. The spots become

dark brown with dead surface tissue, giving the fruit a dirty

appearance.

On peaches and nectarines the fungus forms small, white, circular spots on the surface of the fruit. These spots may enlarge

until they cover most or all of the fruit. Such fruit turns reddish

or pinkish at first and then a dead brown. The underlying flesh is
22 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

rather hard, with a dark, water-soaked appearance. The affected

tissue may extend to the pit (pi. 5, E and F).

Causal factors and control measures

The causal fungus, Sphaerotheca pmmosa var. persicae, is an

obligate parasite, growing only on living tissues of the host plant.

Spores of the fungus infect the fruit early in the season, and after

germinating on the surface are able to penetrate uninjured tissue.

The disease can develop in relatively hot, dry weather, though

some moisture is needed for spore germination.

On eastern fruits, powdery mildew was not a serious problem

until organic chemical sprays replaced sulfur sprays. The disease

can be controlled very effectively with sulfur or with organic chemical sprays containing a small amount of sulfur.

(See 8,160, 210.)

Rhizopus Rot

Rhizopus stolonifer (Ehr, ex Fr.) VuilL

Occurrence

Rhizopus rot is second only to brown rot as the most important

market disease of peaches, nectarines, and apricots. In some

areas rhizopus rot is the only important market disease of these

fruit. Although the disease sometimes occurs in the orchard, it

is found more commonly after the fruit is harvested. Ehizopus

rot develops slowly on immature fruits, but develops rapidly when

the fruits mature and ripen. The disease also develops rapidly

when fruits with long refrigerated storage or transit periods are

transferred to ripening temperatures.

Symptoms

The Rhizopus fungus usually enters the fruit at an injury or

bruise. The first symptom of the disease is a circular, tan area

surrounding an island of apparently healthy skin. Within a few

hours, all the skin in the affected area becomes tan to brown. A

slight pressure applied to the surface causes the skin to slip from

the flesh. As the decay progresses, a fluffy, white growth of mold

appears near the center and rapidly covers the affected area.

White, spherical, spore-producing bodies develop almost immediately, and within 24 hours from the time mold growth first appeared, the white fruiting bodies turn jet black. Finally, the mold
MARKET DISEASES OF STONE FRUITS 23

growth turns gray and multitudes of black spores are produced.

The rot develops rapidly at ripening temperatures, spreading over

an entire fruit v^ithin 48 hours, and from diseased to healthy

fruits, frequently spoiling all the fruit in a box.

The flesh in affected areas is tan, somewhat mushy, and watery.

In advanced stages, the decay extends to the pit and, with pressure

from adjoining fruit, causes the whole fruit to collapse (pi. 2, G

andíí;pl. 6,D, £^, andF).

Causal factors

Rhizopus stolonifer usually infects fruit after harvest, while in

field containers, or during packing, grading, hydrocooling, transport, or distribution. Cuts, cracks, or bruises resulting from

rough handling of the fruit form ideal entrance points for the

organism.

The critical temperature for rhizopus rot is 45° F. The fungus

will not grow nor the spores germinate below 45°. Optimum

spore germination is at 70° to 80° and the maximum slightly above

90°. Other forms of Rhizopus will germinate and grow above

100°. In water at 120° or 130°, Rhizopus spores are killed in 2

to 3 minutes.

Control measures

Sensitivity of the causal organism to low temperature makes

good precooling and refrigeration in storage and transit a primary

control measure. Temperature studies have shown that as much

rhizopus rot develops in peaches held 1 day at 85° F. as in 3 days

at 59°, or 10 days at 50°. The fact that infections occur primarily

through wounds makes careful handling to avoid injuries another

important method of reducing losses from this disease. Sanitation at all stages of handling is important. Heat treating peaches

and nectarines in 125° to 128° F. water for 2 to 3 minutes has

proved an effective method not only for controlling Rhizopus spores

on the surface of peaches and nectarines, but also for controlling

incipient infections of the fruit.

(See 6, 29, 30, 31, 81,115,176,177,179,180,198, 202,)

Ring Pox

Ring pox is a virus disease affecting apricots in southern California, western Colorado, and central Washington. It is indigenous to the areas where it has been found and apparently does not
24 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

spread rapidly to other areas. Apricot ring pox has not been

found outside the United States. Infected apricot trees may be

ruined by the disease, but the virus produces no symptoms on

peaches. Fortunately the disease is not widespread, which limits

its economic importance.

Symptoms of ring pox on apricot fruit do not appear until the

pit starts to harden, and some fruits appear normal until 2 to 3

weeks before they mature. The first symptoms are water-soaked

grey spots and rings on the skin and just under the skin. As the

fruit matures, the discolored areas become reddish purple and

slightly raised and bumpy. The spots turn brown to reddish

brown and several spots may run together and form irregular

blotches over the surface of the fruit. The brown tissue later may

crack and fall out, and when the fruit softens, the brown areas

may extend deeper into the flesh, but never to the pit.

Control of ring pox lies in the selection of disease-free nursery

stock and destruction of diseased trees in the orchard,

(See ^i, 45.)

Rust

Tranzschelia discolor (Fckl.) Tranz. & Litv.

Rust is rarely found on peaches in the market. Usually the

disease is of minor importance, but in some years it may become

epidemic in certain areas. Rust of stone fruits is found in the

Southern and Pacific Coast States. It is primarily a foliage and

bark disease, but occasionally affects the fruit.

Fruit infections occur when the fruit nears maturity. The first

symptoms of rust on peach are water-soaked, dark-green spots,

Vé to i/s inch in diameter, which become sunken as the fruit enlarges. The center of the spot is a darker green than the margin

and later turns deep yellow or orange. The fungus may produce

fruiting bodies in the center of the spots, which appear as darkbrown, dusty areas. The tissue beneath the spots is tough and

leathery and clings tightly to adjacent healthy tissue. This characteristic makes affected fruit difficult to peel, and the resulting

blemishes preclude using the fruit for processing.

Rust infections occur only in the field and the disease does not

spread during the postharvest period. Affected fruits should be

culled in the packinghouse, but a few occasionally reach the market.

(See 8, 57, 74-, 166,185.)
MARKET DISEASES OF STONE FRUITS 25

Scab

Cladosporium carpophiluni Thuem.

Occurrence

Scab occurs in all of the peach-growing areas of the United

States, except Oregon and Washington. Normally the disease is

more serious in States east of the Rocky Mountains than in the

Western States. Nectarines and apricots are affected less seriously than peaches. Since scab originates in the orchard, most

affected fruit should be eliminated in packinghouses before .shipment. However, some peaches with scab appear on the market.

The disease can cause serious economic losses in the orchard, but

is of minor importance as a market disease. Scab sometimes is

called freckles or black spot.

Symptoms

Symptoms of scab on peach fruit first appear when the peaches

are about half formed. Early symptoms are circular, olive-green

spots about 1/16 to i/8 inch in diameter, which may occur singly

or in groups. The spots have rather poorly defined borders at

first, but later the margins become distinct. Scab occurs primarily on the stem end or exposed sides of the fruit, but may occur

anywhere on the skin. The spots enlarge slowly, coalesce, and

turn dark olive or black, due to the myriads of black spores that

are produced. A layer of cork develops below the spots, and as the

fruit develops, it becomes misshapen. Severely scabbed peaches

may crack open, sometimes as far as the pit, thus exposing the

fruit to attack by other decay fungi. Affected fruit usually does

not attain normal size (pi. 5, C and D).

Causal factors

Scab is caused by Cladosporium carpophihim. The fungus overwinters on the twigs and produces spores that infect the young

fruit in the spring or early summer. The spores are produced in

greatest abundance in wet weather and at moderate temperature

(65° to 75° F.) and are disseminated by splashing rains. Symptoms of the disease on the fruit may not be expressed until 1 to 2

months after infection has occurred. Scab is usually more serious

in orchards lying in low, moist areas than in areas with good air

drainage.
26 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

Control measures

Scab can be controlled readily by one orchard application of a

fungicide shortly after petal fall. The disease does not develop

or spread in transit or storage.

(See 8, 60, 83, 87,101, 157.)

Sour Rot

Geotrichum candidiim Lk. ex Pers.

Occurrence and symptoms

Sour rot of peaches has been found in midwestern markets on

fruit from Georgia, New Jersey, North Carolina, and Pennsylvania. In midsummer, about 3 percent of the peaches inspected

had sour rot. The disease is usually associated with bruising or

cutting of the fruit and is particularly prevalent in fruit with split

pits. Sour rot generally affects only ripe fruit, but also may

affect severely bruised green fruit.

External symptoms of sour rot are depressed, dark-brown areas

with purple margins. Later, white masses of spores are produced

on the surface of affected areas. Internally, the rotted flesh is

wet, soft, and dark brown, and occasionally has cavities filled with

masses of white spores. The rot may extend to the pit. Fruit

with split pits aifected by sour rot may not have external symptoms

of the disease, but when cut, the rot is apparent in tissue surrounding the pit. Sour rot has a characteristic vinegary odor (pi.

4,£>).

Causal factors and control measures

The fungus, Geotrichum candidiim, is widespread, growing on

many kinds of fruit, vegetables, and organic matter. Spores of

the fungus may be spread by vinegar flies from decayed fruit to

cracks or bruises in healthy fruit. The spores may also be spread

in picking boxes and handling equipment.

The minimum temperature for spore germination, growth, and

infection by the fungus is about 36° F., the optimum 86°, and the

maximum 101°. At about 60°, the rot spreads very rapidly in ripe

peaches.

Control of sour rot lies in careful handling to reduce bruising,

culling to remove injured or infected fruits that would provide

sources of inoculum, and good sanitary practices during picking
MARKET DISEASES OF STONE FRUITS 27

and packing. Rapid cooling of the fruit and refrigeration at low

temperature will reduce losses from sour rot.

{See 38, 39, H5,)

Plums

Alternaría Rot (Green Mold Rot)

Alternaría sp.

Occurrence and symptoms

Alternarla or green mold rot is occasionally seen in eastern markets on plums and fresh prunes shipped from California, Idaho,

Michigan, and Oregon. A spotting of the fruit, caused by Alternaría sp., has been noted in Canada. The decay occurs in nicks,

cuts, or bruises and in fruit weakened by prolonged storage. Only

small areas are involved, but the decay detracts from the appearance of the fruit.

Alternaria rot appears as a firm, dark-brown to black spot.

The decay is shallow in its early stages, but later may progress to

the pit, forming a cone of diseased tissue. The affected tissue is

firm and can be separated easily from the healthy tissue, the boundaries of the decay being sharply delineated. In late stages the

decayed area is usually covered with olive-green spores of the

fungus, but sometimes a white vegetative growth of mold may

hide the green spores (pi. 7, A).

Causal factors

Green mold rot of plums is caused by one or more species of

Alternaría, which usually enter the fruit through breaks in the

skin. Growth of this mold is most rapid at 85° F., but decay will

develop slowly at transit temperatures near 40°. Other types of

decay may follow alternarla rot. The decay is easily confused

with cladosporium rot, although the latter develops somewhat more

slowly than alternaría rot. Viewing the spores with a microscope

is necessary for positive identification of the rot.

Control measures

Since the causal organism is frequently associated with cuts and

bruises, careful handling to reduce these injuries during harvesting, packing, and shipping will reduce alternarla rot. Quickly

precooling plums to the recommended storage temperature of 31°
28 AGRICULTURE HANDBOOK 414, U.S. DEFT. OF AGRICULTURE

to 32° F. will slow the development of rot and reduce the chance

of new infections.

{^eeJfl,51,112,160.)

Bacterial Spot

Xanthomonas priini (E. F. Sin.) Dows.

Occurrence and symptoms

Bacterial spot of plums is found occasionally in orchards along

the east coast of the United States and in the North-Central and

Midwestern States. Bacterial spot is also known as black spot of

plum. The disease appears as leaf spots, shotholes, cankers on

twigs, and infrequently as spotted and somewhat deformed fruit.

American and European plum varieties are less susceptible than

Japanese varieties, Kelsey and Gaviota.

On the fruit, the disease first appears as small, light-brown to

red spots. In advanced stages the spots become depressed, enlarged, and darker, and may coalesce. A callus may form as a

response to the disease while the fruit is growing ; and when young

fruit are infected, cracks may appear within the depressed area

because of the growth strains involved. When fully growm fruit

become infected, cracks do not develop. A gummy exúdate of the

bacteria may ooze out of affected areas.

Causal factors and control measures

See Peaches, Nectarines, and Apricots, pages 11 and 12.

(See 56, 58,109,153,159,18Jf.)

Blue Mold Rot

Pencillium sp.

Occurrence and symptoms

Blue mold rot is one of the most common rots affecting plums

during storage, transit, and marketing. The disease rarely occurs

in the field, where it affects only mature fruit.

On the market, the rot is associated with cuts, cracks, or other

injury to the fruit. In its early stages, the rot appears as a

bleached or light-brown, circular, fairly soft spot with a definite

outline. Later the skin cracks and white tufts of the fungus appear. The tufts at the center of decay turn bluish green as the

spores are produced, whereas the newer tufts around the rim of

the decay are still white. The decayed ñesh is wedge or saucer

shaped, water soaked, or discolored brown. In advanced stages,
MARKET DISEASES OF STONE FRUITS 29

the decay may encompass the whole plum. Fruits with blue mold

have a musty odor and taste (pi. 7, ß).

Causal factors

See Cherries, page 4.

Control measures

Careful handling of plums to prevent skin breaks and bruises

during harvesting, storing, packing, and shipping will reduce the

incidence of blue mold. Excessively tight packs cause bruises that

favor decay. Rapidly precooling the fruit to temperatures between 40° and 45° F. effectively slows the development of blue

mold in fruit of average maturity. Very mature fruit should be

precooled to temperatures between 35° and 40°.

Plums usually are not stored longer than a few weeks because

of their perishability. Prolonged storage at low temperatures

(31° to 32° F.) predisposes the fruit to blue mold rot.

The use of modified atmospheres during cold storage slows the

ripening of some varieties of plum, thereby reducing susceptibility

to decay. A 7 to 11 percent CO2 level in the atmosphere reduces

ripening rates and decay of Nubiana and El Dorado plums. However, plum varieties differ greatly in their responses to modified

atmospheres ; thus, each should be tested carefully before this procedure is used on large quantities of fruit.

(See 19, il, Jf9, 50,152,160,189, 202,)

Brown Rot

Monilinia fructicola (Wint.) Honey and M. laxa

(Aderh. &RuhL) Honey

Occurrence

Brown rot usually is not as serious on plums and prunes as on

other kinds of stone fruit. However, considerable losses sometimes occur in the eastern part of the United States and the disease

also has caused losses in shipments from California, Idaho, Oregon, and Washington. In the West, the disease is more prevalent

in varieties that mature late in the season than in early varieties. Susceptibility to infection increases as the fruit approaches

maturity.

Japanese and American varieties of plums appear less susceptible than European varieties. No variety of plum is immune to

brown rot. Greatest losses are in those varieties in which the

plums grow in clusters since the fungus spreads rapidly from one

decayed fruit to others in contact with it.
30 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

Symptoms

In light-colored plum varieties, brown rot first appears as a firm

brown spot that enlarges rapidly. The flesh softens as the decay

progresses. In dark plum varieties, the discoloration of affected

areas is not readily discernible at first. As the decay progresses,

the intact skin becomes leathery and dark brown or black. Ashycolored tufts of the fungus and masses of tan spores often occur

on discolored areas. Eventually the fruit shrivels and mummifies

(pl.7,C),

Causal factors and control measures

See Peaches, Nectarines, and Apricots, pages 15 and 16.

(See i6, 61,, 65, 89, 93, 96,108,152,156,163,165.)

Cladosporium Rot

Cladosporium herharum Lk, ex Fr.

Occurrence and symptoms

Cladosporium rot, also called green mold rot, is frequently

found on plums and fresh prunes shipped to eastern markets from

California, Idaho, Oregon, and Washington. The disease is particularly prevalent in fruit held for prolonged storage and transit

periods.

Usually the decayed areas are small and are associated with

nicks, cuts, bruises, or other injuries. In the early stages the decayed spots are shallow and may be overlaid with a white fungal

growth that later produces olive-green spores. The decay may

later extend from the surface to the pit, forming a dark, usually

cone-shaped mass of tissue, which can easily be separated from

the healthy part of the fruit (pL 7, D).

Causal factors and control measures

See Cherries, page 6.

(Seei^, 26, 160,)

Coryneuni Blight

Coryneum carpophilum (Lev.) Jaucb^

Occurrence and symptoms

Coryneum blight of plums has been reported from California to

Idaho and Washington and also from foreign countries. The disease is of field origin and is seldom seen on fruit in the market,

especially in the Eastern United States. The European plum

varieties are more susceptible to coryneum blight than the Japan-
MARKET DISEASES OP STONE FRUITS 31

ese varieties. The disease is also known as shothole, winter blight,

brown spot, and pustular spot. The same organism is one cause

of the European piercing blight.

Symptoms of the disease on the fruit are small red or purplered spots, which gradually enlarge, become depressed, and turn

brown. The centers of the spots remain light in color because of

the formation of dry, corky tissue.

Causal factors and control measures

See Peaches, Nectarines, and Apricots, page 18.

(See 107,160, 17^, 208, 20Í,)

Gray Mold Rot

Botrytis cinérea Pers. ex Fr.

Occurrence

Gray mold occasionally attacks plums in storage and on the

market. It is most prevalent on varieties that are harvested late

in the season and that are exposed to high moisture conditions

before picking. Highly mature fruit is more susceptible to gray

mold rot than less mature fruit.

Infections of plums usually occur through cracks and wounds,

but may also occur by contact when the mold grows from diseased

to adjacent sound fruit, forming ''nests" of decayed fruits. In

California, infections of green fruits have been observed, the

fungus gaining entrance by first infecting adhering flower parts.

In very wet spring weather the Botrytis fungus causes blossom

blight of plums.

Symptoms

In its early stages, gray mold rot is characterized by a lightbrown, firm spot with a distinct boundary. In dark plum varieties

there is a slight fading of the skin color, rather than browning

observed in light varieties. In advanced stages of gray mold rot,

the spot becomes dark brown or almost black and may become

leathery. Internally, the tissues are either water soaked or discolored brown. The affected area becomes covered with a white,

fluffy growth of mold and grayish spore masses. These may be

scanty or abundant, depending upon prevailing humidity and temperature. The decay is softer than brown rot, but not as soft as

blue mold or rhizopus rots. Decayed areas are shallow at first,

but later may extend to the pit. Gray mold has a very slight

earthy odor (pi. 7, E),
32 AGRICULTURE HANDBOOK 414, U.S. DEPT. OP AGRICULTURE

Causai factors and control measures

See Cherries, pages 7 and 8.

(SeeU, 112,131,)

Rhizopus Rot

Rhizopus stolonifer (Ehr. ex Fr.) Vuill.

Occurrence and symptoms

Rhizopus rot is an important disease of plums in transit and in

marketing channels. Various surveys have indicated that, over a

period of years, about 1 percent of the plums and prunes reaching

eastern markets are affected with rhizopus rot. Very ripe plums

are more subject to decay than less ripe fruit.

Rhizopus rot first appears as tan to brown spots on the skin.

Within a day at room temperature, affected areas are covered by

the white, coarse, stringy growth of mold. Small spore-bearing

heads are produced by the mold, which are white at first but later

turn gray or black. The mold forms nests, rapidly spreading

from one fruit to another. In the early stages, the flesh is water

soaked and separates readily from the skin. Later the affected

flesh darkens and the cell walls break down, releasing juice when

the slighest pressure is applied. This condition is known as "leak"

and frequently results in the staining of containers or other objects

in contact with the fruit. The decay has a fermented odor (pi. 7,

F),

Causal Factors

See Peaches, Nectarines, and Apricots, page 23.

Control Measures

The best postharvest control for rhizopus rot is good refrigeration. The causal organism does not grow at temperatures below

45'' F. Precooling plums promptly to this temperature and shipping them at temperatures between 35° and 45° will greatly reduce

the development of rhizopus rot. Most plum varieties are not

adapted to long storage periods so should be marketed promptly.

See Peaches, Nectarines, and Apricots, page 23.

(See 5, 17, 29, 30, U, 120, 179, 202.)

Rust

Tranzschelia discolor (Fckl.) Tranz. & Litv.

The rust disease of plums is usually of little economic importance and is rarely seen on fruit in the market. Most Japanese

and all American varieties may be attacked, although Japanese
MARKET DISEASES OF STONE FRUITS 33

varieties are less susceptible. The disease has been reported on

plums grown in California.

The causal organism, Tranzschelia discolor, affects mostly

leaves, causing premature defoliation. Rusty pustules surrounded

by corky, suberized areas may occasionally develop on the fruit.

The spread of rust in the orchard is favored by rainfall and

high humidity. Postharvest applications with sulfur are effective

against this fungus. Recommendations of local authorities on

control methods should be followed.

See Peaches, Nectarines, and Apricots, page 24.

(See 8, 57, 169,185.)

Scab

Cladosporium carpophilum Thuem.

Occurrence and symptoms

Scab, also known as freckles or black spot, is of orchard origin

and does not spread in storage or in transit. The causal fungus is

widespread, although more serious east of the Rocky Mountains

than in the Western United States. Scab on freshly shipped plums

is occasionally seen during marketing. The poor external appearance of the affected fruit lowers the marketing grade.

The first symptoms of scab are small, circular, yellow spots on

the skin of the fruit. A shallow layer of cells underlying the spot

also turns yellow. Later a brown corky area appears in the center

of the spot. As the spots enlarge, they may coalesce and turn

dark olive or black as the fungus spores develop. Cracks often

develop in the diseased areas, providing entry ports to the organisms causing brown rot, rhizopus rot, and blue mold rot.

Causal factors and control measures

See Peaches, Nectarines, and Apricots, pages 25 and 26.

(See 13,14, 28,1^3.)

NONPARASITIC DISEASES OF STONE FRUITS

Orchard- and Weather-Related Disorders

Cracking

Cracking among the stone fruits is most common in cherries, although plums and peaches occasionally suffer from the disorder.

Estimates indicate that an average of 15 to 20 percent of the sweet

cherries in Michigan crack and that losses in California, Michigan,

Oregon, Utah, Washington, and other States where cherries are

grown often amount to $6 million annually. Most cracking occurs
34 AGRICULTURE HANDBOOK 414, U.S. DEPT. OP AGRICULTURE

in the orchard when fruit is exposed to rain or high humidity

shortly before harvest. Cherries absorb moisture through the

skin and also from the tree ; the moisture may be translocated from

both roots and foliage. More cracking occurs at high temperature

(85° F.) than at low temperature (40''), and cracking increases

as the sugar content of the fruit increases from 17 percent up to

20 to 21 percent; at higher sugar contents, cracking decreases.

The Bing cherry variety is particularly susceptible to cracking;

Black Tartarian, Lambert, Napoleon, Schmidt, and Windsor crack

less than Bing ; and Montmorency cracks less than any of the sweet

varieties. The toughness or elasticity of the skin is a factor in

determining susceptibility of various varieties to cracking.

Cherries crack first in surface areas having the greatest curvature. Cracks may be in the form of deep crescent or V-shaped

breaks in the skin near the apex of the fruit, deep, straight slits

along the sides of the fruit, or circles or semicircles in the stem

cavity. The tissue lining the cracks usually dries out and may

heal over. However, the cracked fruit often become infected with

decay-causing fungi (pL 8, B).

Fresh Italian or French prunes sometimes split or crack along

the sides or on the ends, usually just before ripening. Or growth

cracks may develop in fruits that have been injured at an, early

stage of development by insects; later expansion in the size of the

fruit causes the skin to rupture in the injured areas.

Both peaches and plums sometimes crack as a result of renewed

growth when rainfall follows periods of dry weather (pi. 8, A ). A

defect called open suture affects Stanley plums in Idaho and appears to result from growth stresses along all or a part of the

suture. Late Santa Rosa plums tend to crack at the suture because this part of the fruit ripens first. Nubiana plum is prone

to cracking at various places on the surface. Peaches sometimes

crack when there is an excess of boron in the soil.

Cracking of cherries and some other stone fruits is favored by

rainfall,.the presence of free moisture on fruit and foliage, and

high humidity. Helicopters have been used to dry off the trees

and various cultural practices have been used to increase the transpiration rate of the trees, thereby reducing the turgor of the

fruit. Certain orchard sprays have been effective in increasing

the resistance of cherries and prunes to cracking. Most cracked

fruits are removed in the packinghouse, but some damaged fruits

reach market.

(See 15, 36, U2, 70, 77, 82, 86, 111, lU, 160, 178, 187, 191, 192,

193.)
MARKET DISEASES OF STONE FRUITS 35

Drought Injury

Drought injury primarily affects Italian prunes grown in the

Northwest, although the disorder is found occasionally on prunes

from California, New York, Utah, and other States.

Symptoms of injury are irregular or circular, purple patches on

the skin, which later turn brown. The flesh beneath the affected

areas may also turn brown ; is usually very firm because of dead,

corky tissue; sticks to the pit; and often develops gum pockets.

Finally, the skin breaks over the pockets, forming cracks 14 to %

inch long. The cracks are usually on the cheeks of the fruit and

release a gummy exúdate. Affected fruits usually are culled in

the orchard or packinghouse, but occasionally reach market.

Shriveling (see p. 40) is another type of drought injury.

Shriveling usually occurs at the stem end of the prune and may

extend 14 to 1/3 the length of the fruit. The flesh beneath the

shriveled area turns brown to black. This type of injury is probably due to the withdrawal of water from the fruit by the leaves in

times of water shortage.

^ The effects of drought injury and heat injury (see p. 36) are

difficult to separate because of the similarity of certain symptoms.

Losses from drought injury can be reduced by using vigorous

root stocks, by proper soil management, and, in irrigated orchards,

by proper irrigation practices. Trees that have been injured

previously by cold weather may bear fruit showing symptoms of

drought injury. Drought injury is often associated with boron

deficiency, the tissue and pits of affected fruit being low in boron

content.

(See 20, 37, 78, 155,160, 19^.)

Hail Injury

Stone fruits injured by hail when at an early stage of development have irregular, sunken scars, often with dried segments of

skin and flesh around the edges or on the surface. The injury

may be in the form of small punctures, shallow gouges, deep punctures, or deep gouges that extend to the pit. During development,

the fruit enlarges normally except at the site of the injury, resulting in a misshapen product. Large, gum-filled ducts often form

in the flesh beneath hail scars. Injured areas on peaches may

have a light-red pigmentation ; plums may turn brown at the injury. Hail injury to peaches is usually accompanied by russeting

at the scarred area (pi. 9, A and B).

Hail injury occurs only on one side of the fruit—the side exposed

to hail while the fruit is on the tree. Fruits injured while young
36 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

usually heal over, but sometimes the injured area becomes infected

with decay organisms. Fruits injured near maturity usually do

not heal and soon become unmarketable.

Severely injured fruits are culled during harvesting or packing,

but mildly injured fruits sometimes reach market.

(Seei^O, 168,173.)

Heat Injury

Apricots, prunes, and plums are more susceptible to heat injury

than the other stone fruits.

PIT BURN.—Heat injury to apricots is commonly referred to as

pit burn. At first, the flesh near the pit softens while the outer

flesh remains firm. In a few days the softened flesh turns brown,

but still no evidence of the disorder can be seen externally. Pit

burn develops when exceptionally hot weather occurs between the

time when the fruit begins to lose its green color and when it

becomes ripe enough to harvest. Temperatures of 102° or 103°

F. for 2 or 3 days are sufficient to induce pit burn. The disorder

may develop at slightly lower temperatures on very vigorous

trees. The affected tissue is often attacked by decay-causing

organisms (pi 8, Cando).

INTERNAL BROWNING.—-Italian and French primes are subject

to a disorder called internal browning, which is thought to be

related to weather. First the flesh becomes translucent near the

pit cavity ; later the affected tissue turns brown and breaks down.

In severely injured fruit, the affected area may be quite large and

cavities may develop in the flesh near the pit.

Heat injury to prunes occurs when orchard temperatures remain above 105° F. for extended periods. Fruits that are near

full maturity are more susceptible to the disorder than less mature

fruit. Anaerobic conditions in the inner tissue of the fruit during

periods of high temperature are thought to contribute to heat

injury in prunes. High temperatures (above 105°) also significantly reduce the specific gravity of prunes, thus lowering their

quality.

KELSEY SPOT.—Kelsey plums sometimes suffer from a heatrelated disorder called Kelsey spot. The disorder most commonly

occurs on the distal end of the fruit, although it may occur anyw^here on the fruit. Mildly affected plums have a slightly depressed, reddish, well-defined spot, but severly affected fruit have

larger discolored areas. The flesh below the spot turns brown,

usually about one quarter inch deep, but sometimes the brown tissue extends all the way to the pit.
MARKET DISEASES OP STONE FRUITS 37

Kelsey spot also affects other varieties of plum ; Japanese plum

varieties are more susceptible than European varieties. The disorder is more prevalent on weak trees than on vigorous ones, and

orchards with cover crops show less damage than clean-cultivated

orchards. At temperatures above 105° F., the incidence of Kelsey

spot increases.

(See 35, 55, 67, 68, 8Í, 85, 88, 105, 106, 116, H6, 15i, 19Í, 195.)

Russeting

Russeting is an abnormal roughening and scarring of the surface of fruit, which characteristically is smooth. It commonly

occurs on plums and prunes grown in the Pacific Coast States and

occasionally occurs on cherries and nectarines. Russeting may be

localized on certain parts of the fruit, may occur in patches or

bands, or may cover most of the fruit. Sometimes the disorder is

accompanied by deformities in the shape of the fruit, and russeted

fruit are usually smaller than normal fruit. Bordeaux sprays

tend to make cherries smaller and darker than unsprayed fruit,

though such sprays at recommended concentrations do not cause

russeting.

There are many difí'erent causes of russeting. Frost injury,

spray injury, insect damage, the rubbing of young fruit against

twigs or branches, and various combinations of weather factors

may contribute to russeting.

(See 83, 119, 151, 160, 188.)

Split Pits

Peaches and plums of all commercial varieties occasionally have

split pits. Early peach varieties with fruits that develop rapidly

are particularly susceptible. Blazing Gold, Springtime, Cardinal,

and Royal May are early varieties in which split pits are a problem. Some later varieties such as Red Globe, Fiesta, and J. H.

Hale also tend to produce split pits.

Externally, affected fruits are usually flattened somewhat at the

blossom end and consequently are more spherical than fruit without the disorder. Sometimes a visible crack in the flesh or the

upper end of the stone can be seen in the stem cavity, but in many

fruits, the split pit cannot be found until the fruits are cut.

Fruits with split pits tend to mature faster than normal fruit, so

are more prevalent in the first picking of a particular variety.

Such fruit are edible but do not carry as well as normal fruit during marketing and may become infected with various decay

organisms. Species of Alternaría, Aspergillus, or Pénicillium
38 AGEieULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

may grow on the seed or pit without spreading to the flesh (pL 9,

H).

During normal fruit development, peaches undergo three stages

of growth: A period of rapid growth during the first 40 to 50

days, a period of slow growth during which the pit hardens, and a

final growth swell about 4 weeks before harvest. When abnormal

growth of the flesh occurs during the period of pit hardening, the

pit is torn apart or split, usually along the dorsal or ventral sides.

This abnormal growth may result from weather conditions, an

unusually short crop, high nitrogen conditions in the soil, or the

inhibition of the downward translocation of foods in the tree.

Fruits that develop most rapidly and that have split pits are most

often found toward the ends of branches or in the tops of trees.

Cultural practices that promote excessively vigorous and rapid

growth should be avoided—particularly with varieties that are

susceptible to split pit.

(See 18, 52,118, 1Í7,160, 173.)

Storage-Related Disorders

Aiiinionia Injury

Ammonia injury occurs during precooling or in storage when

leaks develop in mechanical refrigeration systems using this gas

as a refrigerant. Ammonia enters the fruit through lenticels,

through the stem, or directly through the skin.

Peaches exposed to low concentrations of ammonia for a short

period develop minute, greenish-black specks. With longer exposures or higher concentrations of gas, the fruit loses its red

color and becomes a dull, yellowish green. Severely injured

peaches have reddish-brown blotches and large drops of moisture

on the surface. Peaches with ammonia injury shrivel rapidly

when removed from storage and the flesh turns brown, indicating

deep penetration by the gas (pi. 10, A).

Injury to nectarinesis similar to that of peaches, but the surface

tissues of nectarines sometimes become brown and russeted when

exposed to ammonia.

Sweet cherries turn dark blue around the lenficels when injured

by ammonia. The blue color gradually disappears when the fruit

is aerated. In severely injured fruit, the affected tissues turn

brown and shrivel.

Plums injured by ammonia have swollen, discolored lenticels,

which turn dark blue on red fruit and become sunken and brown

after several days (pi. 10, ß).
MARKET DISEASES OF STONE FRUITS 39

Ammonia-induced changes of color from red to blue are thought

to be due to pH changes in the cell sap. Increasing the alkalinity

of the sap causes the color of anthocyanin pigments to change.

Browning, associated with severe injury, is caused by oxidation

reactions in damaged cells of the fruit.

Injury from ammonia can be minimized if the gas is removed

as soon as possible after a leak is discovered. A water spray

in the room is very effective for this purpose because ammonia is

highly soluble in water. If water cannot be used, the room should

be aerated by whatever means available.

(See 54, 148.)

Freezing Injury

See Freezing Injury, page 44.

Internal Breakdown

Most stone fruits are not stored for more than a few weeks. If

stored for longer periods, they are subject to internal breakdown,

loss of flavor, discoloration of the flesh, surface pitting, shriveling,

and predisposition to decay. Some of these disorders may not be

apparent when the fruit is first removed from cold storage, but

develop when the fruit is ripened.

Peaches and nectarines can be stored for about 3 weeks at 31°

to 32° F. without serious loss of quality. With longer storage

periods, the fruit may appear to be normal when removed from

storage, but often develops serious internal breakdown when

transferred to ripening temperatures. The first evidence of

breakdown is a reddish-brown discoloration and a granular texture of the flesh. The discoloration is usually more intense near

the pit than toward the surface of the fruit. Later the flesh becomes a darker brown, often with gray-brown water-soaked areas

extending from around the pit into the flesh. The graininess increases and the affected flesh has a wooly or mealy texture, is

off-flavored, and lacks juiciness. Even in such advanced stages of

breakdown, the fruits usually have a normal external appearance.

Recent studies show that peaches and nectarines can be stored at

31° to 32° in controlled atmosphere with 1 percent oxygen and 5

percent carbon dioxide for 6 to 9 weeks without developing internal

breakdown during storage or ripening. However, with such long

periods of storage, decay caused by Botrytis or Pénicillium may

develop. These organisms normally do not attack freshly harvested peaches (pi. 9, G).

Peaches and nectarines can be stored for a week to 10 days at

40 "" F. without developing internal breakdown during ripening.
40 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

After 3 weeks' storage at 40°, however, internal breakdown is

serious.

Apricots can be stored for 1 to 2 weeks at 31° to 32° F. Apricots packed in polyethylene liners have developed a gel breakdown,

off-flavors, and mealiness, probably due to atmospheres with high

CO2 levels.

Plums or fresh ItaHan prunes can be stored for 3 to 4 weeks at

31° to 32° F., depending upon the variety. Longer storage may

cause the development of breakdown, darkening of the flesh, and

loss of flavor. Stored Kelsey and Wickson plums tend to develop

breakdown, which is more severe at 40° than at the recommended

31° to 32°. El Dorado plums develop a slick, gelatinous texture

and suffer a loss of flavor when stored at temperatures above 34°

for several weeks. Internal breakdown in plums is very similar

to that in peaches, starting near the pit and causing the flesh to

become water-soaked and, later, to turn brown. Also, affected

fruits become mealy and desiccated and develop off-flavors and

abnormal odors. Injured fruits frequently are invaded by various

decay-causing organisms. Modified atmospheres with high CO2

levels have been useful in extending the storage life of El Dorado

and Nubiana plums, but some varieties such as Santa Rosa and

Wickson may be injured by such atmospheres. The use of dual

temperatures, in which the temperature is changed during storage,

has shown promise in reducing cold storage injury to some plum

varieties (pi. 9, C, D,E\ and F).

Cherries can be stored for 10 days to 2 weeks at 31° to 32° F.

When held longer, they sometimes develop elongated, irregular

brownish pitis in the skin. The flesh beneath these spots is discolored brown and tends to dry out, leaving small hollow cavities.

Affected fruit has an abnormal flavor. Injury is frequently followed by decay. Cherries can be stored three times longer at 32°

than at room temperature. A 10 percent CO2 level in controlled

storage atmospheres extends the storage life of Lambert cherries

up to 25 days without serious loss of flavor. Cherries of this

variety stored longer than 25 days in controlled atmosphere lose

quality rapidly and suffer extensive decay when removed from

storage.

(See i, 2, i, 10, 28, 2Í, U, U9, 50, 76, 79,80, 97, 111,, 13i, 135,

137,160,162,175,195,)

Shriveling

Shriveling, due to loss of moisture from the fruit, is a severe

problem of all stone fruits. If listed in order of susceptibility to
MARKET DISEASES OF STONE FRUITS 41

shriveling, nectarines would be first, followed by apricots, cherries,

peaches, fresh prunes, and plums. Defuzzed peaches are almost

as susceptible to shrivel as nectarines. Loss of moisture from

peaches and nectarines not only detracts from their appearance

and eating quality, but loosens the pack within the container,

thereby contributing to bruising. Shriveling of sweet cherry

stems is a serious factor in their loss of fresh appearance and salability. Shriveling is the most extensive form of deterioration of

fresh prunes during storage, and greatly impairs the market quality of the fruit.

Most shriveling is due to the evaporation of moisture from the

surface of the fruits or stems, but some shriveling is due to loss of

moisture resulting from metabolic processes (respiration). Sugars break down into water and CO2 during respiration.

Moisture loss at a given relative humidity is greater at high

temperature than at low temperature and at a given temperature

is greater at low relative humidities than at high relative humidiies. As long as the temperature of the fruit is higher than that

of the air around it, moisture will continue to move out of the fruit

into the air because of a vapor pressure deficit, even at 100-percent

relative humidity. Rapid air movement around the fruit causes

more loss of moisture than slow air movement. Small fruits

generally lose weight faster than large fruits of the same kind

because small fruits have more surface area per unit weight than

large ones and consequently more opportunity for evaporation.

Kinds and varieties of fruit have different rates of moisture loss,

depending upon the texture of the fruit and the type of peel.

Considering the above temperature-relative humidity relationships, the reduction of moisture loss from stone fruits depends

upon the following handling practices : Rapid precooling to bring

the fruit down to storage room or transit temperatures as quickly

as possible; maintenance of high relative humidities (90 to 95 percent) in precooling and storage rooms; the use of protective packaging, such as waxed liners or polyethylene film liners for boxes,

to restrict the movement of moisture from the fruit to the container or to the air outside the container ; and control of air circulation to provide maximum movement for quick cooling, but minimum movement for temperature maintenance after the fruit is

cooled. Hydrocooling is an effective method of precooling some

stone fruits and also serves to moisten wooden containers, thereby

reducing their absorption of moisture from the fruit.

Peaches lose about IV2 times as much moisture at 40° F. as at

33° and lose about 8 times as much moisture per hour during pre-
42 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

cooling as they do after reaching storage room temperature.

Moisture loss is about 21/2 times as great at 76-percent relative

humidity as at 96-percent. These figures illustrate the value of

rapid air cooling or of hydrocooling peaches. Polyethylene liners

are effective in reducing moisture loss from peaches and nectarines,

but cause increased decay losses unless used in conjunction with a

fungicide treatment. Unless ventilated, such liners also may

cause injurious modifications of the atmosphere.

Cherry stems are particularly susceptible to shriveling and discoloration and lose about four times as much moisture as the fruit,

on a percentage of fresh-weight basis. Delayed precooling and

warm, dry environments during wholesale and retail marketing

are much more harmful than the normal time spent in storage or

transit. Rapid cooling in an air blast causes less moisture loss

from the stems than slower cooling in relatively still air. Bruising contributes greatly to the loss ofmoisture from cherry stems.

Polyethylene box liners have been very effective in reducing shrivel

of cherries shipped from the Northwest.

Waxing effectively reduces shriveling of certain stone fruits,

but in some instances may cause an increase in decay. Waxing

of apricots may interfere with normal respiration and thus cause

breakdown and off-flavors.

(See^, 28, iS, 58, 69\ 72, 78,llJf,117,167,182,195,199,)

Sulfur Dioxide Injury

See Sulfur Dioxide Injury, page 46.

Transit- and Handling-Related Disorders

Bruising

Bruising injury is common to all stone fruits, particularly to

peaches, nectarines, apricots, and plums, and is one of the most

important factors contributing to market losses. Bruising may

occur during harvesting, sorting, brushing, packing, car loading,

shipping, or in wholesale or retail marketing. The increased use

of mechanical harvesting for stone fruits has caused an increase in

the percentage of bruised fruits. Because fruits become more

susceptible to bruising as they soften^ they should be harvested at

optimum maturity for shipping. During handling, fruits also

should be of uniform maturity, because running mixed firm and

soft fruits through a sizing line in a packing house causes much

more injury to the softer fruits than running only fruits of near

equal maturity. Delaying the time between picking and packing

also increases losses from bruising.
MARKET DISEASES OF STONE FRUITS 43

Varieties differ in susceptibility to bruising. Springtime

peaches, which have a pointed tip or apex, are prone to injury at

this part of the fruit, whereas Red Haven peaches tend to soften

first at the suture, which favors bruising of this part of the fruit.

Peach varieties also differ greatly in overall firmness. J. H. Hale,

Rio Oso Gem, and Redtop are notable for their firmness and resistance to bruising, whereas many of the very early varieties and

the white-ñeshed varieties are relatively soft and susceptible to

bruising injury.

Symptoms of bruising vary greatly with the type of injury and

the kind of fruit. On light-colored fruit, bruised tissues generally

appear water-soaked or glassy at first and later tend to turn

brown. Dark fruit, such as some varieties of plum, may not show

the discoloration. Discoloration of bruised tissues is greater at

high temperatures (70° F.) than at low (35°). Bruised tissues

frequently develop off-flavors, are usually softer than uninjured

tissues, and dry out when exposed to air. Moderate or light bruising may only blemish the skin, but more severe bruising may cause

breaks that provide entry ports for decay organisms. Since many

of the fungi causing spoilage cannot penetrate the skin of sound

fruit, bruising contributes greatly to these secondary losses from

decay. The amount of decay developing in mechanically harvested

apricots and peaches, for example, is greater than that in handharvested fruit. Bruising also predisposes cherries to scald, a

cause of quality loss in processed fruit.

The causes of mechanical injury to fruits are sometimes divided

into four classes : cutting, compression, impaction, and vibration.

Cutting commonly occurs when fruits strike the sharp points or

edges of equipment or containers ; and fingernail cuts may be inflicted during picking, sorting, or packing.

Compression injury occurs when fruit is placed in over-packed,

bulging containers, w^hen fruit is packed too deeply in a container,

or when containers partly collapse because of weakness, excessively high stacking, or other causes. This type of injury may

occur at points where fruits touch one another or where fruits

touch the bottom, sides, or lid of the box.

Impaction injury occurs at various places during handling.

Warm fruits are generally less susceptible to impaction injury

than cold fruits. Speeding up packinghouse equipment may contribute to this type of bruising. Padding conveyors and sorting,

sizing, and washing machinery to lessen the force of impacts between fruit and machinery parts has helped to reduce losses from

this type of bruising. Care in loading, stripping, and bracing rail-
44 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

cars reduces the shifting of individual packages and consequent

damage from impacts.

Vibration injury occurs when fruits are packed too loosely in

a container and consequently roil or rub against adjacent fruits or

packaging materials during shipment or handling. Brushing or

drying rollers in packinghouses sometimes cause a similar injury.

Cold fruit is less susceptible to this type of injury than warm

fruit. Fruits with vibration injury may appear scalded as a

result of chafing in transit or during handling. Napoleon cherries

or some of the light-colored varieties of plum sometimes show this

type of injury. Enzymatic browning of the surface areas of

plums injured by vibration may be in the form of irregular

patches, may appear as concentric bands around the fruit, or may

affect the whole surface of the fruit. The flesh sometimes turns

brown below affected areas and becomes desiccated. Vibration

injury to apricots resembles that to plums.

Peaches from the Southeastern United States sometimes show

black to purple longitudinal streaks, which sometimes coalesce,

discoloring large areas of the fruit. This disorder is commonly

referred to as black streak. The discoloration appears to be

caused by packinghouse operations in which fruit may rub, roll,

or scrub against other fruit or against equipment. Brushes used

to defuzz or rollers used to dry the fruit are thought to contribute

to the disorder. When injured areas come in contact with iron

salts during washing or hydrocooling, the discoloration becomes

more intense. Normally the discoloration does not appear until

20 to 24 hours after the fruit has been packed and is more severe

on warm than on cold fruit (pi. 10, G).

Pads and box liners reduce compression, impaction, and vibration injury. The tight-fill container has been successful in minimizing injury to cherries, peaches, nectarines, apricots, and plums.

Various types of cup and tray materials also reduce injury. Careful handhng through all phases of harvesting, shipping, and marketing is an obvious and necessary way of reducing losses from

bruising. Prepackaging has helped to reduce injuries incurred

during the retaihng of stone fruits.

(See 27, il, 66, 75, 82, 108, 122, 123, 124, 133, 1U2, 150,

152, 164, 181, 183, 190, 206.)

Freezing Injury

Freezing injury may occur during precooling, in storage, during

transit, or during handling at terminal markets. Because most

stone fruits are harvested and shipped during the summer months,
MARKET DISEASES OF STONE FRUITS 45

freezing usually results from faulty refrigeration practices or

malfunctioning equipment rather than from inclement weather.

However, exposure to frost in the orchard during the growing

period may cause russeting of the fruit, particularly plums or

Italian prunes. Susceptibility to freezing varies with the kind

and variety of fruit and with the maturity. Fruits with high

soluble soHds have lower freezing points than those with low

soluble solids, and as fruits mature, the soluble solids increase.

Also, the stems are more susceptible to freezing than the edible

part of the fruit because the soluble solids are low in the stems.

The place in the handling and distribution sequence where

freezing damage occurred may be indicated by the pattern of

freezing within a container or within a load. For example, containers with frozen fruit scattered at random through a load

suggest that the freezing occurred before loading the fruit in the

railcar or trailer. On the other hand, containers with frozen fruit

located near the outlets of refrigeration ducts or adjacent to the

walls of a car or trailer suggest that the freezing occurred during

transit. Sometimes only the fruit at the sides of the containers

adjacent to a wall of the car or trailer is frozen; this pattern also

would suggest freezing during transit.

Symptoms of freezing injury are a water-soaked, translucent

appearance of the skin or the flesh. The severity of freezing depends upon the temperature drop and the length of time below the

freezing point. When ice crystals form in the tissue, the cells are

crushed or ruptured. The tissues collapse, turn brown, and become soft and mushy. Severely injured fruit is often sticky because of leakage of juice from the injured tissue.

Cherries have average freezing points ranging from 26.2° to

28.2° F., but freezing points may be slightly higher or lower, depending on maturity. The stems may be injured at temperatures

only slightly below 32°.

Peaches have average freezing points ranging from 29.0° to

30.1° F. A low point of 28.4° and a high of 30.3° were found in

different varieties (pi. 10, F).

Nectarines have average freezing points ranging from 28.8° to

30.0° F. A low point of 27.7° and a high of 30.4° were found in

different varieties.

Apricots have average freezing points ranging from 28.9° to

29.9° F. A low point of 28.6° and a high of 30.1° were found in

different varieties.

Plums have average freezing points ranging from 27.2° to 29.8°
46 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

F. A low point of 26.3° and a high of 30.5° were found in different varieties.

(Seeii.4;^0i.)

Shriveling

See Shriveling, page 40.

Sulfur Dioxide Injury

Sulfur dioxide injury occurs when stone fruits are stored or

shipped with table grapes, which are regularly fumigated with the

gas to control decay. Vinifera grapes are about the only fruit not

injured by sulfur dioxide. The injury to stone fruits occasionally

occurs in storage if the gas accidently moves through ducts or

other openings from a room used for grapes to one used for other

fruits. More often, the injury occurs in a mixed load of grapes

and other fruits, which are fumigated in a railcar or trailer. The

person responsible for fumigating the grapes may not know that

other fruits are in the same load.

Sulfur dioxide injury has been observed on cherries, peaches,

nectarines, and plums. The gas causes pitting and bleaching of

all these fruits. Injured areas turn brown, especially when the

fruits are removed from refrigeration. On cherries and plums

the injury occurs at the lenticels, but on peaches and nectarines

the injury occurs anywhere on the surface of the fruit. On

peaches the tissue collapses beneath the browned areas, causing

them to lose moisture and become sunken. Sometimes the skin

of peaches sloughs off when injured by sulfur dioxide (pi. 10, C,

D, and£7).

(See 56, 160.)

INSECT INJURIES

Damage to stone fruits by insects, once very common on the

market, is now rarely found because of improved methods of controlling insects in the orchard, better sorting and grading of fruit,

and generally improved handling and marketing methods. Some

injuries caused by insects are difficult to distinguish from plant

diseases or physiological disorders, and fruit so injured occasionally is found on the market.

Catface

Peaches and other stone fruits may be pitted, dimpled, scarred,

or otherwise distorted as the result of damage by sucking bugs.
MARKET DISEASES OF STONE FRUITS 47

Severely distorted or "catfaced'' fruits result from injuries that

occur when the fruits are small, and subsequent growth of tissue

around the injured areas causes the abnormally shaped fruit. Injuries that occur when the fruits are larger cause less distortion

and result in dimpled or pitted fruits. Such fruit are sometimes

mottled since the skin at the bottom of the dimples remains

green. Peaches injured near maturity may develop dried out,

corky areas around the feeding sites of the insects. Injuries from

sucking bugs may occur anywhere on the surface of the fruit, but

most often are near the stem end. Injuries form entry ports for

brown rot and other decay organisms. The insects that cause

catface usually have left the fruit when the injury becomes apparent. Consequently, the kind of insect causing the injury is

difficult to determine (pi. 8, E).

Several kinds of insects cause catfacing. The tarnished plant

bug {Lygus lineolaris (Palisot de Beauvois) ) occurs throughout

the United States and seriously injures peaches. In California,

a lygus bug (Lygus hesperus (Knight)) causes catfacing in

peaches and nectarines. The brown stinkbug (Euschisttis servies

(Say)) and the green stinkbug (Acrostermim hilare (Say)) are

widespread in the Southeastern United States, the former causing

catfacing and the latter dimpling, since the green stinkbug usually

feeds on peach fruits after they have already enlarged. The Consperse stinkbug (Euschistus conspersus Uhler) and the Say stinkbug (Pitedia sayi (Stal)) cause catfacing in California. The

former also causes dry, corky areas to develop under the skin of

peach, apricot, and plum fruits. Several other species of sucking

bug may cause catfacing. Under some conditions the plum curculio (Conotrachehis nenuphar (Herbst)) causes a similar injury

to stone fruits. Injury by this insect may result from either egg

punctures or feeding. Heavy infestations of thrips (see p. 49)

sometimes cause catfacing of nectarines in California.

Many of the sucking bugs hibernate as adults in winter, becoming active in the spring. Certain species predominate at bloom,

others are most abundant a few weeks after bloom, and some are

present during the entire growing season. Since weeds, cover

crops, and orchard trash favor the build-up of these pests, ridding

the orchard of these breeding places is helpful in reducing injury.

Cultivation also interrupts the life cycle of the plum curculio. An

insecticide recommended by the local agricultural agent should be

applied at bloom time and at intervals thereafter to reduce injury.

(See 21J^, 216, 217, 218, 219, 220,)
48 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

Fruit Gumining

"Gumming'' frequently occurs at sites of insect activity on stone

fruits. The exudation of gum from the tissues of the fruit may

be stimulated by the feeding of adult insects, the entrance or exit

of larva from the fruit, or the deposition of eggs beneath the skin

of the fruit. The rupture or puncture at which gumming may be

partly surrounded by a crescent-shaped slit, which persists on

smooth-skinned fruits such as plum, but generally disappears on

developing peach fruits. Fruits injured early in their development tend to exude large quantities of gum, whereas those injured late may not heal at all and are subject to decay. The

incidence of brown rot is closely correlated with insect injuries.

Sometimes the injury does not appear to be extensive on the surface, but a large cavity may occur beneath the opening or the flesh

may be almost completely consumed by larvae within the fruit

(Pl. 8,^).

Certain bacterial and fungal diseases may also cause gumming.

These diseases, however, are readily distinguished from insect

injuries, which are characterized by tunneling within the flesh,

the presence of a powdery frass, or the larvae themselves.

Several species of insect may cause gumming of stone fruits.

The adult plum curculio frequently feeds on young peach fruits

and the females lay their eggs in the fruit. The larvae develop

within the fruit, which then tends to drop from the tree. The

oriental fruit moth (Grapholitha molesta (Busck)) also causes

gumming but the larva is the only injurious stage of this insect.

The larvae enter the partly mature fruits through either the stems

or the sides and feed on the flesh near the pit. Peaches are injured most by this insect, but other stone fruits also may be attacked. The oriental fruit moth is an important cause of gumming in peaches grown in both the Eastern and Western United

States. The larvae of the peach twig borer (Ariarsia lineatella

Zeller) attack the fruits of peach, apricot, and plum. The peach

twig borer is most serious on the Pacific Coast although it also

causes loss in other stone-fruit growing areas of the United States.

The peach twig borer is controlled by dormant sprays in some

localities, but in California additional bloom and postbloom sprays

are recommended. The oriental fruit moth and the plum curculio

are more difficult to control, requiring additional sprays during

the growing season and good orchard sanitation to eliminate the

culled fruit in which larvae develop. Clean cultivation of orchards helps reduce the population of these insects.

(See 214, 215, 216, 217, 218.)
MARKET DISEASES OF STONE FRUITS 49

Thrip Injury

Thrip injury is confined to the surface of fruits. Cherries,

peaches, nectarines, apricots, plums, and prunes are sometimes

scarred or russeted by thrips, particularly in the Pacific Coast

States and to a lesser extent in the Eastern United States. Nectarines and prunes are injured more often than other fruits.

Thrips feed by rasping the surface of the fruit or other plant parts

and sucking- out the sap exuded from the injured cells. They also

injure young fruit by depositing eggs in the stems, which usually

causes the fruit to drop. Injury often occurs where leaves or

flower parts touch the fruit, the thrips feeding on both the protected leaf and fruit surfaces. Fruit damage is greatest during

the interval between petal fall and shedding of the calyx. The injury appears as a stippling, mottling, russeting, or silvering of

the skin, which is generally lighter in color than unaffected areas

of the fruit. The discolored area may be whitish, grayish, or

yellowish, depending upon the background color of the fruit.

Nectarine fruits that are severely injured when small may become

distorted as they mature. Injured areas on smooth-skinned

fruits, such as prune or nectarine, frequently become checked or

pitted (pi. 8, G),

Several species of thrips may injure stone fruits. The pear

thrip {Taeniothrips inconsequens (Uzel) ) commonly injures

prunes in the coastal valleys of California. The western flower

thrip {Frankliniella occidentalis (Pergande) ) commonly injures

stone fruits in central California.

Thrips usually do not cause sufficient damage to warrant the

application of insecticides. However, either prebloom or residual

bloom sprays provide effective control. Clean cultivation of orchards and elimination of weeds help reduce thrip populations.

{See 213, 215, 216, 217.)
50 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

LITERATURE CITED

General

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(2) _

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1944. CARBON DIOXIDE INVESTIGATIONS: DRY ICE AS A SUPPLEMENT TO

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1915. THE TEMPERATURE RELATIONS OP SOME FUNGI CAUSING STORAGE

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1925. RHIZOPUS ROT OF PEACHES. Phytopathology 15: 122-124.

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(8)

1926. OVERWINTERING OF BACTERIUM PRUNI. Phytopathology 16: 55-

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1956. BROWN ROT OP STONE FRUITS, IV. ON THE PEACH IN WET AND

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MARKET DISEASES OF STONE FRUITS 51

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1959. FLUORIDE INJURY OR SOFT SUTURE AND SPLITTING OF PEACHES.

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1930. LENGTH OF TH.E FRUIT DEVELOPMENT PERIOD OF THE ELBERTA AND

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1951. PRUNE DISEASES. Idaho State Hort. Soc. Trans. 57th Ann.

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1939. RELATION OF DROUGHT SPOT OF PRUNES TO BORON CONTENT OF

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1942. RING SPOT OF APRICOT. Phytopathology 32: 179-181.

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1959. BROWN ROT OF STONE FRUITS. So. Austral. Dept. Agr. Jour. 63 :

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1955. EFFECT OF POLYETHYLENE (POLYTHENE) WRAPPERS ON THE KEEPING QUALITY OF APRICOTS, PEACHES, AND PLUMS. Farming in

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(26) and WIANT, J. S.

1942. DISEASES OF FRUIT AND VEGETABLES ON THE NEW YORK MARKET

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1931. DISCOLORATION OF NAPOLEON (ROYAL ANN) CHERRIES. U.S.

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52 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

(29) BROOKS, C.

1933, SPOILAGE OF STONE FRUITS ON THE MARKET. U.S. Dept. Agr.

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1921. TEMPERATURE RELATIONS OF STONE FRUIT FUNGI. U.S. Dept.

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illus.

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1952. A STUDY OF SOME INORGANIC COMPOUNDS AND GROWTH PROMOTING CHEMICALS IN RELATION TO FRUIT CRACKING OF BING CHERRIES AT MATURITY. Amer. Soc. Hort. Sei. Proc. 59: 243-253.

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1960. PATHOGENICITY AND TAXONOMY OF GEOTRICHUM CANDIDUM.

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1932. CORYNEUM BLIGHT INJURES MICHIGAN PEACHES, Mich. Agr.

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MARKET DISEASES OP STONE FRUITS 53

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(44) and ALLEN, P. W.

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(46) CORBIN, J. B. ' '

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MARKET DISEASES OF STONE FRUITS 55

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1958. TRANSIT INJURY TO FRESH FRUITS. Conf. Transportation Perishables, Davis, Calif., Proc. 1958: 76-81.
62 AGRICULTURE HANDBOOK 414, U.S. DEPT. OP AGRICULTURE

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1960. FRESH FRUIT TEMPERATURES AND TRANSIT INJURY. Amer. Soc.

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1952. IDENTIFICATION AND CONTROL OF BACTERIAL SPOT OF STONE FRUIT.

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64 AGRICULTURE HANDBOOK 414, U.S. DEPT. OF AGRICULTURE

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Agriculture Handbook 414, U.S. Dept. of Agriculture PLATE 1

PARASITIC DISEASES OP CHEBET

A, Altemaria rot of cherry ; B, Blue mold rot of cherry ; C, Brown rot of cherry ;

D, Cladosporlum rot of cherry ; E, Gray mold rot of cherry ; F, Rhizopus rot

of cherry.
PLATE 2 Agriculture Handbook 414, U.S. Dept. of Agriculture

PARASITIC DISEASES OP APEICOT

A, Alteraaria rot of apricot ; B, Coryneum blight of apricot ; C, Brown rot of

apricot (early stage) ; D, Brown rot of apricot (late stage) ; E, Gray mold

rot of apricot (early stage) ; F, Gray mold rot of apricot (later stage) ; O,

Rhizopus rot of apricot (early stage) ; H, Rhlzopus rot of apricot (late

stage).
Agriculture Handbook 414, U.S. Dept. of Agriculture

PABASITIC DISEASES OF PEACH

A, Gray mold rot of peach (early stage) ; B, Gray mold rot of peach (intermediate stage) ; 0, Gray mold rot of peach (advanced stage) ; X>, Alternarla

rot of peach; E, Blue mold rot of peach (early stage) ; F, Blue mold rot of

peach (advanced stage).
Agriculture Handbook 414, U.S. Dept. of Agriculture

PABASITIC DISEASES OP PEACH

A, Black mold rot of peach (early stage) ; B, Black mold rot of peach (advanced

stage) ; C, Diplodia rot of peach ; D, Sour rot of peach ; E and F, Coryneum

blight of peach ; G, Anthracnose of peach.
Agriculture Handbook 414, U.S. Dept. of Agriculture PLATE 5

PARASITIC DISEASES OF PEACH

A, Bacterial spot of peach (early-season infection) ; B, Bacterial spot of peach

(late-season infection) ; C, Peach scab (early-season infection) ; D, Peach

scab (late-season infection) ; E, Powdery mildew of peach (on green fruit) ;

F, Powdery mildew of peach (on ripe fruit).
PLATE 6 Agriculture Handbook 414, U.S. Dept. of Agriculture

Si»

PABASITIC DISEASES OP PEACH

A, Brown rot of peach (early stage) ; B, Brown rot of peach (intermediate

stage) ; C, Brown rot of peach (advanced stage) ; D, Rhizopus rot of peach

(early stage) ; E, Ehizopus rot of peach (intermediate stage) ; F, Rhizopus

rot of peach (advanced stage).
Agriculture Handbook 414, U.S. Dept. of Agriculture PLATE 7

PABASITIC DISEASES OP PLUM

A, Altemaria rot of plum ; B, Blue mold rot of plum ; C, Brown rot of plum ; D,

Cladosporium rot of plum ; E, Gray mold rot of plum ; F, Rhizopus rot of

plum.
PLATE 8 Agriculture Handbook 414, U.S. Dept. of Agriculture

B

NoNPARASiTic DISEASES

A, Cracking of plum ; B, Cracking of cherry ; C and D, Pit burn of apricot.

INSECT DAMAGE

E, Catface of peach ; F, "Gumming" of peach ; G, Thrips damage of nectarine.
Agriculture Handbook 414, U.S. Dept. of Agriculture PLATE 9

t ^'#

A, Hail injury to peach (early-season injury) ; B, Hail injury to apricot (lateseason injury) ; C, Physiological (internal) breakdown of plums (external

symptoms) ; H, E, and F, Physiological (internal) breakdown of plums (internal symptoms) ; O, Internal breakdown of peach ; H, split pit of peach.
Agriculture Handbook 414, U.S. Dept. of Agriculture

NONPARABITIC DISEASES

A, Ammonia injury to peacli ; B, Ammonia injury to plum ; C and D, Sulfur dioxide injury of nectarine ; E, Sulfur dioxide injury to plum ; F, Freezing

injury to peach ; G, Black streak injury to peach.

A U.S. GOVERNMENT PRINTING OFFICE : 1972 0—426-471