Market Diseases

of

Cabbage, Cauliflower, Turnips,

Cucumbers, Melons, and

Related Crops

«• S. OEPT. Of AGíHCütn«E|

UPRARV

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^wnm spRMi Kectms

Glen B. Ramsey and M. A. Smith

Agriculture Handbook No. 184

UNITED STATES DEPARTMENT OF AGRICULTURE

Agricultural Marketing Service

Market Quality Research Division
THIS REPORT is one of a group of publications on market diseases

of fruits and vegetables. The publications are designed to aid in the

recognition and identification of pathological conditions of economic

importance affecting fruits and vegetables in the channels of marketing

in order to facilitate inspection of these food products and to prevent

losses from such conditions.

Other reports on market diseases of fruits and vegetables issued by

the U.S. Department of Agriculture include :

Miscellaneous Publications

98. Potatoes. Revised Jan. 1949.

168. Apples, Pears, Quinces. Revised Nov. 1951.

228. Peaches, Plums, Cherries, and Other Stone Fruits. Revised Feb. 1950.

340. Grapes and Other Small Fruits. July 1939.

440. Asparagus, Onions, Beans, Peas, Carrots, Celery, and Related Vegetables. Sept. 1941.

498. Citrus and Other Subtropical Fruits. June 1943.

Agriculture Handbooks

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

June 1952.

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

Artichokes, Lettuce, Rhubarb, Spinach, and Sweetpotatoes. April 1959.

Miscellaneous Publications 228, 340, and 440 are out of print but

may be consulted in libraries.

This publication supersedes Miscellaneous Publication 292, "Market

Diseases of Fruits and Vegetables; Crucifers and Cucurbits."
t

Market Diseases

Cabbage, Cauliflower, Turnips,

Cucumbers, Melons, and

Related Crops

Agriculture Handbook No. 184

UNITED STATES DEPARTMENT OF AGRICULTURE

Agricultural Marketing Service

Market Quality Research Division

September 1961

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

Washington 25, D.C.
CONTENTS

Page

Crueifers 1

Cabbage 1

Alternaría leaf spot 2

Bacterial soft rot 3

Bacterial zonate spot 4

Black leaf speck 4

Black rot 5

Downy mildew 6

Freezing injury 7

Gray mold rot 8

Mosaic 9

Rhizoctonia head and root

rots 9

Rhizopus soft rot 10

Sunscald 11

Thrips (Edema) 11

Tipburn 11

Watery soft rot _ 12

Chinese cabbage 13

Brussels sprouts 13

Broccoli 14

Cauliflower 14

Bacterial leaf spot 14

Boron deficiency 15

Brown rot 16

Ring spot 16

Collards and kale 17

Cress 17

Horseradish 17

Bacterial root rots 18

Pénicillium root rot 18

Rhizoctonia root rot 18

Kohlrabi 18

Mustard 19

Radish 19

Black spot 19

White rust 19

Rutabaga and turnip 20

Alternarla root rot and leaf

spot 20

Anthracnose 20

Clubroot 21

Cucurbits 21

ii

Page

Cucumber 21

Anthracnose 22

Bacterial spot (angular leaf

spot) 23

Black rot 23

Cottony leak 24

Low temperature breakdown 24

Mosaic 25

Scab 25

Soil rot 25

Muskmelon 26

Alternarla rot 26

Anthracnose 27

Bacterial soft rot 28

Bacterial spot 29

Blue mold rot 29

Charcoal rot 30

Cladosporium rot 30

Diplodia rot 31

Fusarium rot 32

Low temperature breakdown. 33

Phytophthora rot 33

Pink mold rot 34

Rhizopus soft rot 35

Pumpkins 36

Squash 36

Alternarla rot 36

Black rot (gummy stem

blight) "_ 37

Blossom end rot 37

Watermelon 38

Anthracnose 38

Black rot 39

Blossom end rot 40

Bruising (mechanical injury) 40

Charcoal rot 40

Fusarium rot 41

Internal rind spot 41

Phytophthora rot 41

Watermelon pimples 42

Pythium rot 42

Sclerotium rot 43

Soilrot 43

Speckle 43

Stem end rot 44

Literature cited 45
Market Diseases

of

CABBAGE, CAULIFLOWER, TURNIPS, CUCUMBERS,

MELONS, AND RELATED CROPS

By GLEN B. RAMSEY, principal pathologist,^ and M. A. SMITH, senior pathologist, Market Quality Research Division, Agricultural Marketing Service

CRUCIFERS

The various members of the crucifer group supposedly are horticultural varieties which have been developed by cultivation from the

wild Brassica olerácea. Thus the headless types (kale and coUard,

etc.) "are B. olerácea var. viridis L.; the budding type (brussels

sprouts), var. gemmifera DC; the floral head types (cauliflower and

flowering broccoli), var. hotrytis L. and var. itálica Plenck; the enlarged stem type (kohlrabi), var. caulo-rapa L.; and the leafy head

type (cabbage), var. capitata L.

CABBAGE

Cabbage is used for food as salad and as a cooked vegetable, and

a considerable amount is fermented and eaten as sauerkraut. Cabbage, like most other cultivated crucifers, belongs to the genus

Brassica.

The marketability of cabbage for table purposes is affected by

many factors, the foremost being crispness, solidity of head, color,

and freedom from blemishes and decay. Since field diseases often

affect the crispness, solidity, and color of cabbage, they are both a

direct and an indirect factor in its marketability.

Lack of crispness may be due to poor growing conditions, to field

diseases, to excessive drying out in storage, or to the respiratory

activities of the tissues. Excessive loss of crispness because of respiration may result from too high a temperature during transit and

storage or from too long a transit or storage period.

Several diseases which seriously affect production may also directly

affect the marketability of the heads. Foremost among these is black

rot {XantKonwnas camfestris (Pam.) Dows.). Others are alternarla

leaf spot {Alternaría hrassicae (Berk.) Sacc. and A. olerácea Milbrath), bacterial leaf spot {Pseudomonas iimculicola (McCull.) F. L.

Stevens), downy mildew {Peronospora parasítica (Fr.)), and

Rhizoctonia head rot {PelliculaHa filavientosa (Pat.) Kogers).

iNow retired.
There are several diseases which only occasionally cause losses in

the field, but Avhich are exceedingly important in the later stages of

distribution and in storage. These are bacterial soft rot (Enmnia

carotovora), gray mold rot {Botrytis cinérea (Pers.)), rhizopus soft

rot {Rhizojma stolonifer (Fr.)), and watery soft rot {Sclerotinia

sclerotiorum (Lib.) DBy). Often these also cause heavy indirect

losses in transit and storage by necessitating heavy trimming.

(See 10, 11, 26, 27, k6, 6k, 68, 89, 101, lOl^.y

ALTERNARíA LEAF SPOT

A\\Qtnat\a spp.

Occurrence and Importance

Alternaría leaf spot is a widelj' distributed disease that occurs on

cabbage, cauliflower, broccoli, and most other plants belonging to the

mustard family. In wet seasons this leaf spot has been known to

reduce the yield of cabbage by more than 50 percent. The market

losses are due to decay which develops in transit and storage, to

secondaiy decay for wliich it opens the way, and to blemishes which

render the heads unsightly and necessitate heavy trimming.

Symptoms

The first symptom of alternaría leaf spot is the appearance of

small grayish-brown to black spots about i/^e inch in diameter (pi.

3, F). They may appear at any time during the life of the cabbage

plant. They usually are most conspicuous on the outer, older leaA^es.

The color of the spots depends somewhat on the color of the part of

the leaf aiïected. Old spots may range up to 1 inch or more in

diameter. Sometimes the spots produced by A. hrassica-e are marked

by light- and dark-brown concentric zones that produce a "target

board" appearance. A growth of dark brown to black mold is often

present in a humid atmosphere (pi. 1, B). The spots caused by

A. olerácea are not zonate and usually are not covered by a moldy

growth until the leaves turn yellow or are shed. Bacterial soft rot

and other secondary decay sometimes follow in these lesions.

Causal Factors

Three species of Alternaría have been reported as causing leaf spot

of plants belonging to the mustard family. A. hra,ssicae is generally

thought to be the cause of most losses, although A. olerácea also

causes serious damage in some regions. Under moist conditions the

spores of these organisms may germinate and cause infection within

24 hours. The spores germinate best between 63 and 70° F. Wounds

are not necessary for infection. Although most infections are prominent on the wrapper and older head leaves, the age of the plant apparently has little to do with the infection. High humidity and

moderate temperatures favor the spread and development of this

disease. Low temperatures (35^5° F.) and low humidity greatly

inhibit infection and decay.

Control Measures

Severely spotted heads of cabbage and other plants of this family

should be closely trimmed before shipment. Shipments to distant

' Italic numbers in parentlieses refer to items in the Literature Cited, p. 45.

2
markets should be refrigerated to 40-45° F. during transit. Cabbage

to be held in storage for any great length of time should be kept at

35° F. or slightly below.

{See 89,93.)

BACTERIAL SOFT ROT

Erwinia carotovora (Jones) Holland and other bacteria

Occurrence and importance

Bacterial soft rot of cabbage and other members of the mustard

family often causes serious losses during marketing. This is because bruised and wounded tissues are readily atfected, and the causal

organism is a secondary invader of tissues killed or weakened by

most of the parasitic and some nonparasitic diseases. It often follows black rot, clubroot, downy mildew, or alternarla leaf spot, and

causes most of the damage following freezing.

Ordinarily, soft rot is of little importance in the field except as a

secondary invader following other diseases. At times dead and

dying heads in the field develop soft rot and in cutting the crop for

marketing the knives become contaminated, thus leading to infection

of subsequent heads. Such heads show stump or butt rot by the time

they reach the market (pi. 3, C).

Symptoms

On cabbage and brussels sprouts the first symptoms usually show

as watersoaked or greasy spots on the leaves as biiiises or as white

to grayish, soft areas at tlie base of the heads. Small lesions have

no appreciable odor but extensive decay has a very putrid odor.

INHien this disease follows black rot and other diseases frequently a

large proportion of the head is converted into a brownish-black slimy

mass.

On the curds of cauliflower the first evidence of infection is small,

yellowish, slightly Avatersoaked specks in the florets (pi. 6, B). As

the decay progresses, the affected florets become darker yellow, more

watery and somewhat sunken. The most serious type of bacterial

soft rot is developed in cauliflower when large yellowish-brown areas

resulting from pressure bruises in packing and handling become

infected.

Although bacterial soft rot is usually not of much importance in

shipments of broccoli it sometimes appears as dark green watersoaked

or greasy lesions at bruises on the leaves and flower heads.

Causal Factors

The bacterial soft rots of vegetables are caused by Erwinia carotovora or closely related organisms. The bacteria of this gi'oup are

ever present in vegetable-growing regions, but they are unable to

invade plants except through wounds, through lesions produced by

other diseases, or through tissues injured by freezing, asphyxiation,

or ao-ino-. Moist surfaces or injured tissues which lead to bleeding

of the plant juices generally provide the water and food necessary

for growth and reproduction of the soft rot bacteria. Warm, wet

weather favors the development and spread of the disease m the held,

and warm, moist conditions favor its development and spread m

transa Temperatures between 69° and 77° F favor the disease

because there ís less drying out of tissues. At 91° the orgamsm does
not. grow as well as at 69° ; at 61° it produces only one-half and at

54° only one-third as much rot as at 69°, while at 46° there is practically no invasion of tissues.

Control Measures

The control of bacterial soft rot in vegetables during transit and

marketing involves careful trimming to eliminate other diseases,

careful packing and handling to avoid unnecessary wounds, and good

refrigeration in transit and while held in stores. Vegetables should

be kept at 45° F. or below to effectively check the development of

bacterial soft rot.

(See 9.7.)

BACTERIAL ZONATE SPOT

9%Qiiáomona% cichori'i (Swingle) Stapp

Bacterial zonate spot is primarily a disease of cabbage although

other members of the Cruciferae and Cucurbitaceae are susceptible.

It was first observed on Florida-grown cabbage in the Chicago market in 1953.

The disease is characterized by round to irregular lesions y^e to I/2

inch in diameter, at first buff to light brown, becoming darker brown

with age. The lesions are zoned or targetlike and may occur on any

part of the leaf (pi. 3, D). Superficially the lesions resemble those

caused by Alternaría hra-Hsicae on cabbage. Infected areas are firm

and pliable but only slightly soft. This is in contrast to the slimy

type of decay produced by Erwinm carotovora.

The casual organism, Pseudomonrts cichorii (Swingle) Stapp,

enters cabbage through wounds. Lesions may occur on any part of

the leaf but there is no evidence that the disease involves the vascular

system. Best growth of the pathogen occurs at 75° F. Control

measures have not been developed.

(See 73.)

BLACK LEAF SPECK

Black leaf speck may occur in cabbage, Chinese cabbage, and cauliilower from all sections. It occurs commonly in transit and storage

and sometimes m the field. The spots render these products unslightly, thus affecting their marketability.

Black leaf speck is characterized by small, sharply sunken, brown

or black specks occurring anywhere on the leaves of cabbage, cauliflower, and Chinese cabbage (pi. 2, A and pi. 9). At times they are

found m great abundance, especially on the leaf blades. These

specks may occur m a few of the outer head leaves of cabbao-e or in

leaves throughout the head. Frequently, it is difficult to distinguish

them from the early stages of Alternaría spot in cabbage, and from

ring spot m cauliflower.

Very little is known about the cause of black leaf speck. However, a similar type of leaf spotting of cabbage is known to be caused

by a virus (see Mosaic, p. 9). Its occurrence under refrigeration

m transit and storage and in association with decided drops in temperature m the field suggest that this trouble is in some way related

to low temperature. Black leaf speck has been produced experimentally by placing cabbage in a well-ventilated room at temperatures near 32° F. for 2 or 3 weeks.

No effective control measures are known.

(See 52.)
BLACK ROT

Xanthomonas campestr'is (Pam.) Dows.

Occurrence and Importance

Black rot is often one of the most serious diseases of cabbage, cauliflower, and related vegetables of the mustard family. The disease

is a market factor because it produces discolorations in the leaves

and stems of affected plants and because it opens the way for secondary infection by bacterial soft rot which often causes serious loss

during marketing. When the heads are not affected throughout,

some salvage can be effected by trimming off blemished or decayed

leaves.

Symptoms

Black rot is a vascular disease. It is not a soft rot, although it

niay be complicated by soft rot. Often the first symptoms of this

disease are yellow and light-brown spots or patches at the margin of

the leaves. The veins in affected leaves appear as a black, conspicuous network and in the midrib where the vascular tissue is covered

by light fleshy tissue there is a dark shadow running through the

center. This black stain often extends into the compact head leaves

of cabbage and down the stem (pi. 2, B). Part or all of the vascular

ring in the stem may be discolored, but the pith and cortex generally

are not involved (pi. 2, A). Even extensively invaded cabbage heads

may remain firm. However, on the market the base of the stem and

the outer head leaves often become soft due to secondary invasion by

bacterial soft rot.

Although black rot in cauliflower usually develops as in cabbage,

it sometimes manifests quite different symptoms. In very rainy

weather the leaves of cauliflower that are invaded by the black rot

bacteria may wilt quickly without showing the usual black discoloration of the veins. When infection of the lower leaves occurs on the

under surfaces where waterdrops form, often large watersoaked

lesions are j)roduced and the leaves wilt and dry, causing the plant

to have a blighted appearance.

In kohlrabi affected with black rot, the staining of the vascular

elements often is very pronounced in the enlarged stem without

visible external symptoms. In Chinese cabbage numerous small

brown spots may occur on the leaf blade, and the vascular tissue also

shows discoloration. In rutabagas the roots may not show external

symptoms of the disease but on cutting, the brownish-black stained

specks in the vascular ring and in the center of the root are very

conspicuous (pi. 8, A). In none of these commodities is there a

definite odor associated with black rot lesions unless some secondary

oro^anism has invaded the affected tissues. to

Causal Factors

The bacterium causing black rot may overwinter on the seed, on

the mother cabbage heads, in plant debris, or in the soil. Infection

often occurs in the cotyledons of the plants m the seed bed. Most

infections in cabbage and other plants of this family occur through

the water pores, in the margins of the leaves. -^ r; ,i

The time of the appearance of black rot and the seventy ot the

Hi<?Pfl"5P is laro-elv determined by weather conditions. Warni, rainy

weatlfer wiS^Sderately cool rights is most favorable for infection
and spread of the disease. Hot, dry weather is unfavorable for the

development of black rot.

Black rot does not spread or develop appreciably in transit or

storage under refrigeration but secondary decay caused by bacterial

soft rot sometimes progresses sufficiently to make it seem to have

advanced.

Control Measures

Cabbage heads with badly discolored wrapper and outer head

leaves and discolored stems should not be packed for shipment.

Slightly infected heads may be salvaged by close trimming, but there

is always some danger of secondary bacterial soft rot causing trouble

during marketing, unless a temperature of 40° to 45° F. or lower

is maintained.

(See 15.)

BORON DEFICIENCY

See Cauliflower, p. 15.

DOWNY MILDEW

Peronospora parasítica [fr)

Occurrence and Importance

Downy mildew occurs on members of the mustard family from

many regions. The disease is of market significance chiefly on cabbage, cauliflower, radishes, and turnips. In the seed beds and in the

field it causes death of young plants during cool, wet weather and

blemishes many plants that survive so that their market value is

reduced. Downy mildew is sometimes a very destructive disease of

radishes and cabbage on the market and in storage.

Symptoms

The first symptoms of leaf infection are small, pale, greenishyellow angular spots. As the spots enlarge, a fine white downy

mildew becomes evident on the underside of the leaves. As long as

the weather remains wet, new spots continue to appear and the older

ones enlarge and become yellowish brown. Wlien severely spotted,

the older leaves are shed, but the newer leaves become infected as

long as the weather is favorable. This leads to spotting of the outside leaves, which sometimes detracts from the market value ípl.

3,E).

Wlien the fungus enters the stalk at the base of the old headleaves

of cabbage, a grayish-black discoloration of the stalk occurs (pi. 4,

B). In some storage lots of cabbage this discoloration has been

found extending up through the stalk to the innermost bud leaves.

The discolored pith and parenchyma tissues are practically as firm

as the healthy tissues. There is no odor and no surface growth of

mold visible. However, secondary infections by Rhizopus, Alternaría, and bacteria sometimes produce rot in the discolored areas.

Heads of cauliflower may also show the same grayish-black discoloration of the stalk and thickened branches of the flower head as

in cabbage (pi. 4, A).

"When maturing turnips are heavily infected with downy mildew,

the fungus sometimes follows down the leaves into the crown of the

root. Freshly invaded root tissues show brown mottling or streaks

extending from the crown into the root. Affected turnips in storage

sometimes have most of the central part of the root blackened by tlus
fungus. This discoloration resembles that caused by boron deficiency,

but in general it is blacker and not so watery. As in other instances

of invasion of fleshy parts of vegetables, no soft rot is produced, and

in topped turnips there is no external evidence of infection.

Affected radishes show brown to black discolorations of the epidermis generally about halfway down the side of the roots. The

discoloration has no particular pattern. Sometimes there is an

elongated streak, but usually the discoloration is blotchy and frequently spread around the circumference of the roots (pi. 7, A).

Internal flesh of the roots is firm and grayish brown to black (pi.

7,B).

Causal Factors

The causal fungus Peronospora parasítica overwinters in the form

of resting spores (oospores) in debris of affected plants of the previous year m the soil and as perennial mycelium in wild and cultivated

plants of the mustard family. Infection spreads rapidly during wet

weather but dry, warm weather stops sporulation and spread of the

disease. Sporulation may occur on infected leaves and roots in

storage or in transit. The spores germinate abundantly at 46° to

about 65° F. and may cause new infections. Infections become

visible in 3 days at about 70°. There is a rapid development of

disease in infected tissues at 75°.

Control Measures

Cabbage and cauliflower heads and radish and turnip roots showing grayish-black discolorations of the fleshy tissues should be sorted

out at the packing shed. Transit and storage temperatures below

40° F. should retard the development of this disease.

(See 32, 62, 63.)

FREEZING INJURY

Heavy losses of cabbage occur annually as a result of freezing,

both in the field and after harvest. Cabbage tissue has one of the

highest freezing points (31° F.) found among vegetables. Although

cabbage tissues differ from those of many other vegetables, in that

they can tolerate some formation of ice and thawing without apparent injury, there is a limit below which they are likely to be injured. Sometimes frozen cabbage will thaw out without injury and

sometimes it will not. In the former case the tissues are merely

frozen, while in the latter they have been killed. However, there is

no way of telling by examination of a frozen head of cabbage

whether it will show injury when thawed out. Immediately after

thawing, the frozen areas appear watersoaked due to suffusion with

water liberated by the thawing ice in the intercellular spaces. If

the cells are still alive, some of the water will go back into them and

the only effect in the tissue is a slight wilting or shriveling due to

the excessive loss of water. Tissues responding m this way become

flaccid, pithy, or spongy and tough, and lose their characteristic

flavor Some of them can withstand freezing several times before

the effect becomes pronounced; others develop it the first time It

the cells are not alive, the water does not reenter them and is either

lost rapidly into the air, with attendant drying out of the tissues,, or

t reSnsLd the tissues become a leaking ¿--^X'tW o?nï c

is attacked by saprophytic fungi and bacteria. Wliether or not ice

Lmatiofin the tissue! is attended by permanent injury and death
seems to depend upon how low the temperature is, the rate at which

it falls, the duration of the freezing temperature, and the condition

of the plant tissues.

Frozen leafy tissues and even such storage tissues as turnips and

rutabagas lose their natural luster and take on a glassy appearance.

Immediately upon thawing they become watersoaked. The leafy

green tissues in the watersoaked area also have a dirty or muddy

green color. In colorless or fleshy parts like cauliflower heads there

is no discoloration at first. Later the more sensitive tissues, especially the fibrovascular bundles, may become yellowish brown and

finally black. Fleshy roots such as turnips, radishes, rutabagas, and

horseradish often show no discolorations, except in the vascular

tissues.

In cabbage the outer leaves seem to be more resistant to killing by

freezing than the inner leaves and the stem. Generally they thawout W'ithout injury. After prolonged exposure to freezing temperatures, the inner tissues, especially the pith of the stem, usually are

killed and soon become afí'ected with bacterial soft rot.

Control is obtained by avoiding exposure of the products to freezing temperatures for a long enough period to cause their death.

{See 104.)

GRAY MOLD ROT

Botrytis cinérea Pers.

Cabbage, cauliflower, broccoli, turnip, and rutabagas are the chief

members of the mustard family that are attacked by the gray mold

rot fungus. This organism is widely distributed and occasionally

causes serious damage to crops grown in very humid regions. This

disease may cause damage to the growing crops, but it is usually

inore important as a transit and storage disease. The marketable

A^egetable produce is contaminated by spores during harvesting and

packing operations. The spores germinate readily in moist packages

of vegetables. Once infection has occurred appreciable rot may develop even under standard refrigeration practices.

On green leafy tissues of cabbage, cauliflower, and brussels sprouts

greenish brown, watersoaked areas are produced. Usually a fine

white mold is apparent on the surface of the larger spots. In more

advanced stages, the decayed areas become grayish brown and the

surface mold becomes brown also when clusters of spores begin to

form (pi. 3, B). In fleshy tissues such as cauliflower curd, turnip,

and rutabaga roots, the affected portions are gray to light brown

and are fairly moist. Gray mold rot is a moist type of decay but

not so wet or leaky as is produced by Rhizopus soft rot, or watery

soft rot. The diseased tissues have no odor except that of the juices

of the plant itself. However, produce which is warm usually becomes infected by bacterial soft rot which produces a disagreeable

odor.

Since the gray mold rot fungus is able to make noticeable progress

even m temperatures of 35 to 40° F., decay is commonly found in

refrigerated shipments and in cold storage. Best control of this

decay can be obtained by carefully sorting out all produce showing

decay at the packaging shed and keeping the commodity as cold as

possible during transit, storage, and marketing. Produce showing

infection will continue to develop decay even at 32°, but at a slower

rate.

8
MOSAIC

There are many kinds of mosaic disease on cabbage and other

menabers of the mustard family. Most members of the mustard

family are more or less affected during the growing season, sometimes with serious loss. Affected plants are seldom seen on the

market because the conspicuously mottled and discolored produce

is not shipped. Occasionally cabbage is found on the market with

numerous internal black specks that are characteristic of one kind

of mosaic. There is no decay but the appearance of the heads

greatly reduces their market value. (See Black Leaf Speck, p. 4 )

(See l^k, 52, 60, 8Jf.)

RHIZOCTONIA HEAD AND ROOT ROTS

Rhizocfonia sofani Kuehn (Pe/Zicu/aria fi/amen/osa (Pat.) Rogers)

Occurrence and Importance

Various crop plants belonging to the mustard family are subject

to attacks by the common soil fungus Rhkoctonia. Head rot of cabbage and root rot of turnips and radishes are the most important of

the resulting market diseases. Under favoiable conditions one or

more of the various types of disease induced by this fungus may

occur in any of the vegetable-growing sections of the country.

Symptoms

The lesions induced by Rhhoctonia may usually be recognized by

the moderately coarse, cream-colored to brown surface mycelium and

the irregularly shaped chocolate-brown sclerotia of the fungus. The

affected tissues are light brown and semiwatery at first and change

to dark brown or brownish black as the fungus extends deeper and

the tissues dry. Toward midseason the cabbage plants that escaped

serious previous infection may show dark lesions on the stem and

lower leaves, bottom rot, or later dark-brown sunken lesions on the

stem, midribs, and blades of the compact head leaves. This latter

phase, known as head rot, is especially damaging to cabbages ready

for market, Ibecause of the ability of the fungus to continue development during transit and while in storage. Heads so affected are

also subject to bacterial infections that mduce rapidly developing,

foul-smelling decay.

The root rots of turnips, rutabagas, and radishes caused by

Rhizocfonia are sometimes important in the field, but in many instances most damage is done in storage. The fungus may enter

through the leaf scars or injuries at the crown, or through infected

rootlets. The lesions are usually round and light brown. As the

fun<nis grows deeper into the tissues the affected area becomes dark

brown and slightly sunken and the internal tissues become semiwatery or spongy as water is lost by evaporation. Frequently the

spots in storage turnips are made up of concentric rings of lightand dark-brown tissues. Brown surface mycelium and sclerotia of

the causal fungus may or may not be present.

Causal Factors

The sterile form of the fungus {Rhizoctonia solani) is by far the

most important cause of this disease. This stage of the fungus is

ever present in the soil of most vegetable-growing districts, whereas
the spore-forming stage {Pelliculaña flainentosa) is rarely seen.

Under humid conditions the fine creamy-white mycelium and minute

granular spores may be found on stems and the under sides of lower

leaves of cabbages and other plants, but the spores do not survive

long in dry air, and it is doubtful if they ever are important disseminating agents.

The Rhizoctonia stage of the fungus is pathogenic to a great number of plants, and it withstands adverse weather remarkably well.

It is able to survive in soils at freezing temperatures and below and

is not killed at 100° F. The hard, compact masses of mycelium

(sclerotia) may be expected to maintain the life of the fungus in

practically any climate.

Several strains of this fungus are recognized, some being able to

attack one plant, some another. The strain that causes bottom rot

and head rot of cabbage will grow in culture at 48° to 91° F., but

the minimum temperature for infection of cabbage is near 53°, the

optimum 77° to 80°, and the maximum 88° to 90°.

For growth in culture the strain of Rhizoctonia that causes rot of

turnips has its minimum at about .35° F., optimum 73°, and maximum 89° to 94°. The minimum temperature for infection of turnips

is about 35°, the optimum 66° to 77°, and the maximum between

84° and 90°.

Except for very low or extremely high temperatures the most important limiting factors in determining infection and decay by

Rhizoctonia are soil moisture and humidity. Since this fungus does

not require wounds for producing infection it may attack practically

any part of a plant with which it comes in contact, providing there

is enough moisture to permit it to grow on the surface tissues long

enough to gain entrance into them. Once the hyphae have invaded

tlie tissues they will continue to develop and cause decay regardless

of external moisture, although high humidity always favors rapid

development of decay. In storage, high humidity favors infection

and decay ; low humidity limits both.

Control Measures

Cabbage, turnips, rutabagas, or radishes that show severe Rhizoctonia infection should not be shipped or stored. Slightly affected

products may be stored for a month without excessive loss, if the

temperature is held at 32° to 34° and the humidity is kept as low as

possible without causing wilting.

(See 26, 89.)

RHIZOPUS SOFT ROT

Rhizopus stolon'ifer Fr.

The members of the mustard family are often subject to infection

and decay by Rhizopus. This fungus is ever present in the air and

soil, and consequently there is always more or less danger from infection if conditions are favorable. Excessively wounded or bruised

stock is especially susceptible to infection if warm, humid conditions

prevail. This disease is of little or no consequence in the field or on

leafy crops such as mustard and kale, but sometimes considerable

loss occurs in the more ñeshy vegetables such as cabbage, brussels

sprouts, cauliñower, turnips, and rutabagas on account of decay developing during transit and marketing. The chief predisposing factors are wounds and high temperature.

10
The decay in succulent tissues is light brown, soft, and watery ; in

root crops tlie rot is moderately soft and moist, but it lacks the

disagreeable but characteristic odor of the bacterial soft rots that

sometimes present a similar appearance. Usually in cabbages, cauliflower, brussels sprouts, and turnips the coarse, stringy mycelium

bearing white and blaciv sporangia make the diagnosis of" this disease

fairly easy (pi. 5, C).

Rhizopus does not affect cabbage, cauliflower, or root crops stored

near 32° F. The minimum temperature for the development of

Ehizopus rot is about 44°, the optimum between 77° and 82°, and

the maximum about 90°.

(See 54, H-)

SUNSCALD

In cabbage, scald usually occurs only on leaves that are exposed

on the top of the head. The first symptom is a watersoaked or

blistered, irregularly shaped area, which promptly dries out and

becomes a bleached, papery, or parchmentlike island surrounded by

healthy tissue.

The scalded area either remains parched and bleached or is invaded by bacteria that cause soft rot and such fungi as Rhizopus sp.

and Altemarm sp.

Affected leaves should be removed before the cabbage is shipped

or stored.

THRIPS INJURY (EDEMA)

Thr'ips tabaci Lind.

Cabbage on the market in some seasons shows considerable damage

by thrips. These small insects, just visible to the naked eye, feed

upon the leaves and cause blemishes that sometimes greatly injure

the appearance of the heads. These insects puncture and rasp off

the epidermis and suck the juice from the injured tissue. "Valiere

extensive feeding has occurred the surface of the leaves presents a

yellowish-brown scarified appearance when the injured tissues begin

to dry (pi. 5, A). In many instances these insects work up through

open spaces between the head leaves and in feeding there cause injuries that apparently stimulate proliferation of the epidermal cells

so that an edema type of growth is developed (pi. 5, B). These

superficial pustules of white or yellowish cells are usually i/ie to i/ginch in diameter. Thrips appear to be constantly associated with

this edema type of development between the basal head leaves as

well as with the scarified rusty patches on the outer leaves.

TIPBURN

Tipburn of cabbage is most common in the Northern States. It

frequently causes much damage to cabbage grown in soil deficient in

potash and comparatively high in nitrogen. In seasons of severe

drought, death and discoloration of the leaf margins (a type of tipburn) sometimes occur. _ Cabbage showing tipburn is greatly discounted on the market because of appearance and the loss entailed in preparing it for table

use Affected stock, whether in the field, in transit, or in storage, is

also subject to invasion by decay-producing organisms, such as bacteria, Alternaría, Ehizopus, and Botrytis.

11
Characteristic symptoms of this disease are yellowing, browning,

and gradual drying of the leaf margins. Frequently the outer head

leaves are the only ones affected and these may be trimmed off before the cabbages are marketed, but in some instances the tips of the

leaves a fourth of the way through the head may show yellowish or

grayish-brown discoloration.

tíontrol of tipburn has been obtained by application of potash

fertilizers to some soils; to others a heavy dressmg of stable manure

has been found beneficial.

(See 65.)

WATERY SOFT ROT (Sclerotinia Rot)

Sc/erof/ni'a sc/erof/orum (Lib.) DBy.

Occurrence and Importance

Among the most serious diseases of vegetables are those caused by

soil organisms. Watery soft rot is caused by a soil fungus which is

more or less common in all regions that grow vegetables, and is especially destructive because it can attack a wide variety of crops.

Symptoms

A characteristic soft, watery decay is produced and affected tissues

are often covered with a white cottony mold (pi. 1, A). In transit,

storage, and on the market badly decayed products actually leak, but

there is no disagreeable odor like that produced by many other diseases. In dry air the water frequently evaporates as fast as it is

liberated and the tissues dry down into a mummy or into parchmentlike remnants. Succulent tissues in moist air generally are completely liquefied, so that a pool of juice with the characteristic odor

of the plant tissues is all that remains. The color of the lesions

varies widely wdth various hosts and indi^àduals. When the lesions

are moist they appear watersoaked, with little change in color. Frequently the borders of the lesions are pink and the inner portions

are yellow or light brown.

The disease generally occurs in the basal part of plants or in the

parts near or lying on the soil. However, the fungus is not limited

to these parts; it can attack the floral parts 3 to 4 feet above the

ground.

In storage and in transit the fungus frequently makes a vigorous

and compact growth that spreads from one individual to another

and enmeshes them in its mycelium.

The fungus itself furnishes a good means for identifying the disease for it usually develops a luxuriant, white, cottony mass of

mycelium which is so characteristic that the disease sometimes is

known as cottony rot. Even more characteristic are the large restinobodies or sclerotia, which form when the ñuigus begins to dry out

or when the food supply begins to wane. These are white at first

and later turn black. Large sclerotia are often formed on affected

cabbage, rutabagas, and turnips in storage.

Causal Factors

The disease is caused by a fungus, Sclerotinia sderotiorum. It

persists ni the sclerotial stage in the soil and becomes active when

moisture and temperature conditions are favorable. Cabbage be12
comes infected by mycelium that grows from the sclerotia or by

spores that are produced in apothecia and shot into the air.

Watery soft rot may develop in transit or storage in stock which

appeared sound when harvested but which came from a field infested

with the fungus. Plants taken from fields free from ScUrotima will

not develop the rot unless they come in contact with other diseased

plantsor soil contaminated with the fungus. A few infected cabbages in a package may be sufficient to cause complete decay of the

entire contents. Although the fungus does not need- wounds for

entry, wounded tissues become infected more readily than others.

Severity of the rot increases rapidly w-ith rising temperatures

until the optimum temperature for growth is reached between 70°

and 78° F. At 88° to 90°, there is practically no growth. Under

the most favorable temperature and moisture conditions, the first

symptoms may appear within 6 to 48 hours after infection, and the

tissue ma,y be completely destroyed in 3 to 5 days.

After infection has taken place the rate of development of the

lesions is less dependent upon moisture than upon temperature. If

the stock comes from an infested field and is put into storage or

shipped, or if it is put into contact with stock already affected,

severe losses may occur even at temperatures between 32° and 45° F.

Low temperatures will, however, slow up the development and

spread of the rot.

Control Measures

Affected products should not be packed or stored.

Although low temperatures do not completely control the disease,

they retard its development so much that precooling and good transit refrigeration are highly desirable.

(See 19, 61.)

CHINESE CABBAGE

The Chinese cabbage or petsai {Brassica pekinensis) is a member

of the mustard family and is related to the common cabbage. It

does not form compact heads, but a more or less open, soft mass of

leaves. The factors governing the marketability of Chinese cabbage

are essentially the same as those of the common cabbage. The most

important market diseases are bacterial soft rot, black rot, and black

leaf speck (pi. 9).

(See Cabbage, p. 1.)

BRUSSELS SPROUTS

Brussels sprouts are the buds of a member of the mustard family

{Brassica olerácea var. gemmifera). Desirability of the buds depends primarily upon crispness, tenderness, and freedom from blemishes and decay. Essentially the same diseases that affect cabbage

and other cruciferae affect this plant in the field and the buds after

harvest. The most important market and transit diseases are bacterial soft rot, alternarla rot, Rhizopus rot (pi. 5, C), and black rot.

Eing spot (pi. 5, D) also affects brussels sprouts.

(See Cabbage, p. 1, and Cauliñower, p. 14.)

13
BROCCOLI

The term broccoli refers to the green, loosely formed floral heads

and associated tender leaves and stems of the plant Brassica olerácea

(var. itálica Plenck). This plant is subject to many of the diseases

found on cauliflower. The most important market and transit diseases are bacterial spot (pi. 3, A), bacterial soft rot, gray mold rot

(pi. 3, B), and watery soft rot.

(See Cauliflower, p. 14.)

(See VJ, 72.)

CAULIFLOWER

The cauliflower is the malformed condensed flower head with short

fleshy branches of a plant {Brassica olerácea L., var. hotrytis) very

closely related to the cabbage. By breeding and selection, strains

have been developed which produce firm, smooth, white, well-rounded

flower heads or curds, and these are greatly in demand on the market.

In the best cauliflower, the outer leaves or jackets are green, the

enclosed head is creamy white to white, and the bud clusters are

crowded closely together forming an even, firm head. Good heads

will remain compact for a short time in the field, and under proper

conditions will carry well in transit, maintaining good marketable

condition for some time.

Since the market demands green jackets, any disease that spots the

leaves or that causes premature yellowing or dropping is important.

Cauliflower is subject to the same diseases that affect cabbage and

other members of the Cruciferae. Some of these diseases are especially important. Those that either blemish or decay the curd are

more important than those primarily affecting the leaves. The most

important diseases are: bacterial soft rot, black rot, bacterial leaf

spot, downy mildew, brown rot, gray mold rot, ring spot, and watery

soft rot.

BACTERIAL LEAF SPOT

Pseudomonas macu/ico/a (McCull.) F. L. Stevens

Occurrence and Importance

Bacterial leaf spot is a minor disease of cauliflower, cabbage, and

broccoli found occasionally in the field and on the market. It is

prevalent on cauliflower and broccoli grown in the San Francisco

Bay district in California, but it has also been reported from Virginia, Florida, and New York. The disease disfigures the leaves of

cabbage, the stems and florets of broccoli, and the leaves and curds

of cauliflower, thus reducing their market value.

Symptoms

On cauliflower the disease is characterized by abundant specking,

spotting and blotching of the green leaves, on and between the veins,

as well as on the flowerheads. Lesions on the leaves appear as very

small, watersoaked spots, of variable size, with dark specks in the

center. The spots often coalesce, thus becoming irregular in shape,

giving the leaf a ragged appearance. Severely affected leaves turn

yellow and fall prematurely.

14
Lesions on the curds appear as small gray to brown spots on the

epidermis and deeper tissues of the buds and branches. The affected

tissues are firm at first but later may become soft if invaded by

secondary organisms.

The disease on broccoli is characterized by purplish gray to black

lesions varying in size from mere pin points to circular or oblong

spots %o inch in diameter on stems, petioles, florets, and leaves. Infections on stems sometimes coalesce to form lesions 14 inch in lensth

(pl.3,A).

Causal Factors

The causal organism Psettdommms macuJicoIa enters through

stomata. Infection is most abundant on the lower leaf surfaces. It

has been observed that the disease is more likely to occur on cauliflower curds that are slightly overmature and on those showing

slight injuries. The disease does not occur duiing hot weather. The

optimum temperature for the oi'ganism in culture is 75° to 77° F.,

minimum is 32°, and maximum is 84°. Infection becomes visible in

about 3 days on leaves and in 7 to 9 days on stems and flower heads.

Development of the disease in storage and transit should be retarded by temperatures near 32° F.

(See 4>, 72.)

BACTERIAL SOFT ROT

See Cabbage, p. 3, and plate 6, B.

BORON DEFICIENCY

Boron deficiency can cause browning or bitter brown rot on most

cultivated crucifers, but cabbage, cauliflower, rutabaga, and turnip

are particularly sensitive. This trouble has caused considerable loss

to cauliflower in Maine, New York, Wisconsin, and Florida and

other areas where it is grown.

In cabbage showing boron deficiency a brown necrosis develops in

the fleshy pith of stem and core. The first noticeable symptom of

the deficiency in cauliflower is a slight brownish discoloration of the

curd. Blisters and cracks may appear on midribs of leaves and

brown necrotic areas develop in the pith of stems. In advanced

stages, the discolored pith shrinks and cracks and the stems become

hollow. Although the head may become brown, it remains firm unless bacteria or other secondary decay-producing organisms enter.

Symptoms of boron deficiency or brown heart in rutabaga and

turnip are similar. Severely affected plants are dwarfed and have

curlecl, rugose leaves. In advanced stages watersoaked or brown

spots and cracks appear in the interior of roots. These internal

brown discolorations sometimes completely destroy the market value

of rutabagas. . , , ^ ^^

Boron deficiency of broccoli is characterized by curling, rolling,

and discoloration of the leaves. Severely affected plants have

cracked petioles, corky growths on the stems and petioles, and brown

buds in the heads or flower clusters. Discolored flower buds are

bitter and spotted heads are not salable. ^ ^ ^ .

Ten to 20 pounds of borax per acre is usually sufficient to correct

the disease in cabbage, cauliflower, and radish.

The disease does not increase after harvest.

(See 10,11, 20, 21, 26, 30, k9, 85.)

15

553801°—61 2
BROWN ROT

Alternaría brassicae (Berk.) Sacc.

Occurrence and Importance

Brown rot is caused by the same organism tliat causes black leaf

spot or black mold on other members of the cabbage family. The

lesions on curds of cauliflower, however, are known as brown rot.

The importance of the disease is due to its effects upon the curd in

transit and in storage.

Symptoms

The symptoms of the disease are essentially the same as those

found on cabbage and other members of the Brassicae. On the curd

the fungus causes a browning of individual buds or groups of buds

(pi. 6, A). Lesions at first are light brown, later darkening to

chestnut brown and finally becoming olivaceous in color. Under

humid conditions a slight amount of grayish-brown mold may develop over the larger lesions. Infected curds may show numerous

spots or at other times large blotches. The lesions may be dry and

firm or wet and soft so they may be confused with the lesions caused

by bacterial leaf spot or by soft rot organisms.

Causal Factors

The causal fungus, Alternarm brassicae, winters over in the soil

and in the debris of the infected plants of the previous season. The

spores of the fungus live over winter on the seed. From these

sources the seedlings become infected, and on them are produced the

spores that serve as inoculum for other plants.

At 35° F. and at relative humidities varying from 74 to 100 percent, lesions are formed in 5 to 7 days but do not penetrate deeply

into the curd. At 60° they form in 3 days and penetrate into the

curd. The optimum temperature for development of the disease is

about 77° F. Cauliflower, when harvested, may appear to be free

of brown rot but visible lesions may develop during transit. Upon

arrival at the market such cauliflower may show considerable decay.

Control Measures

Low temperatures in refrigerator cars and trucks may not entirely

stop the development of the disease but they do materially retard it.

Packaged heads sliould be precooled at shipping point and shipped

in refrigerator cars or trucks held at 40° F. or lower during transit.

(See 6i, 91.)

DOWNY MILDEW

See Cabbage, p. 6, and plate 4, A.

RING SPOT

M/cosphaere/Za brassic/co/o (Fr.) Lindau

Occurrence and Importance

Eing spot may afl'ect various plants belonging to the mustard

family but is seldom of economic importance except on cauliflower

grown in California and Oregon. Cabbage, brussels sprouts (pi. 5,

16
P), kale, and rutabao^as are sometimes spotted by this disease. Radishes and white turnips have not been found affected.

Badly spotted and yellowed leaves injure the marketability of

affected stock even though the heads are suitable for use.

Symptoms

Practically all parts of the plant are susceptible to infection. The

young spots are small and circular with dark centers surrounded by

greenish-yellow watersoaked borders. As the spots enlarge, they

usually maintain their circular outline and have light-brown to

grayish-brown centers surrounded by narrow olive-green or olivegray borders. The black pycnidia and perithecia may appear in

concentric rings toward the outer part of the central region or be

scattered promiscuously over it.

Causal Factors

The causal organism MycospliaerelU hrasi-icicola lives over from

season to season on the old leaves, stems, and seed pods of affected

plants and may live for some time in the soil. Moderately low temperatures and high humidity favor development of the disease. The

lesions are usually about a month old before the small fruiting bodies

of the fungus have developed sufficiently to make a definite diagnosis

of ring spot.

Control Measures

Experimental evidence tends to show that few, if any, new lesions

will form if cauliflower is held at 32° F.

(See 92.)

COLLARDS AND KALE

Collards and kale are horticultural varieties of a nonheading type

of cabbage plant {Brassica oleráceas var. viridis.). Both are subject

to many diseases that occur on cabbage and other members of the

mustard family. Bacterial soft rot {Erwinia carotovora) is the most

important disease in transit and on the market. Yellows {Fusarium

conglutinans Wr.) is a market factor at times because of the foliage

discoloration associated with it.

CRESS

The name "cress" is used for several species of crucifers that are

used in salads and for garnishing. The leaves of the common garden

cress {Lejndium sativum) and water cress {Radícula nrnturtium

aquaticum) are most often found upon the market. The marketability of cress depends upon the color, tenderness, crispness, and

freedom from blemishes and decay of the foliage. Few diseases

affect this group of plants while they are young enough to be marketed as cress. Bacterial soft rot may cause some damage in badly

wounded or bruised stock during transit and marketing,

HORSERADISH

Horseradish is the fleshy, white taproot of Armoraoia rusticana

Gaertn., a member of the mustard family. The marketability of this

17
product depends chiefly upon the size and smoothness of roots and

freedom from growth cracks.

Plorseradish is subject to a number of field diseases that reduce the

vitality of the plant and in cases of severe foliage infection indirectly influence the marketability of tlie roots. The virus diseases,

mosaic and curly top, and fungus and bacterial root rots which may

occur either in the field or in storage pits may cause serious losses.

Mosaic and curly top are the two most important virus diseases

aiïecting horseradish. Infected roots are usually much smaller than

normal roots and are always brittle. Such roots show pronounced

discoloration in the vicinity of the vascular strands. As the disease

progresses the discoloration darkens until in most cases it is black

Ijy the time the plant is dead. The roots of infected plants are unsuitable for sets and are unsalable on the market.

(See 38, 59.)

BACTERIAL ROOT ROTS

Bacteria spp.

Several types of root rots attributed to E. carotovora and other

bacterial organisms have been reported from New Jersey. Over 60

distinct species of bacteria have been isolated from horseradish in

Illinois. Some of the species caused discoloration, some soft rot,

and some dry rot. Observations showed that the bacteria present

were often able to bring about decay whenever they gain entrance

through various types of injury.

(See 38.)

PENICILLIUM ROOT ROT

Pénicillium hirsutum Dierckx

A root rot caused by Pénicillium hirsutum occurs on horseradish

stored in pits. Losses of stored sets have been reported to be as high

as 40 percent. The decay caused by this fungus is somewhat similar

to that caused by RMzoctonia except that the fungus sporulates

abundantly, coating the diseased surface with greenish-blue spore

masses and rendering them unsuitable for planting or the market.

RHIZOCTONIA ROOT ROT

Rhizoctonia solani Kuehn

Ehizoctonia root rot has been reported on horseradish in New

York, New Jersey, Connecticut, Illinois, and Michigan. Root tissue

infected with Rhizoctonia rot is light yellow to grayish tan in color

and rather dry. Infected tissue separates readily from the advancing

edge of the rot. As the infection progresses brownish-black sclerotial bodies produced by the fungus may be seen scattered in the

creamy-white mold on the surface of the roots.

(See 66.)

KOHLRABI

Kohlrabi is the swollen, fleshy stem of Brassi^a olerácea var. oaulorafci, a member of the mustard family. The stem usually is marketed with the leaves attached. The most important factors determining its marketability are tenderness, absence of woodiness, and

18
freedom from blemishes and decay. The plant is subject to many

diseases that attack cabbage but few of these are direct market

factors. Bacterial soft rot (p. 3) is tlie most important disease.

MUSTARD

The mustard plant [Brassiea spp.) is grown commercially for two

purposes : for the seeds which yield oil and are used as a condiment,

and for the leaves, which are used for greens. The marketability of

mustard for greens depends upon good green color of the leaves and

freedom from blemishes and decay.

The mustards are not often seriously affected by disease, although

they are susceptible to most of the diseases which attack other crucifers. The marketability of mustard is most generally affected by

such diseases as bacterial soft rot, alternaria leaf spot, and white rust.

RADISH

The radish is the fleshy taproot and hypocotyl of Rcqylianus

sativus, a member of the mustard family. Although only the root

is eaten, radishes may be marketed in bunches with the tops attached.

Consequently the appearance and condition of the tops as well as of

the roots are market factors. The main market requisites for the

root are tenderness, crispness, and freedom from pungent taste, blemishes, and decay.

BLACK SPOT OF RADISH

(Cause Unknown)

Prepackaged radishes from Florida and Texas often show small,

sunken discolored spots with well-defined margins. These spots are

grayish brown to black with centers of lighter shade (pi. 7, C).

When internal tissues are affected they are generally black and in

various stages of disintegration. As a rule, examinations fail to reveal the presence of any organisms until the spots have reached an

advanced stage when many kinds of bacteria, considered to be secondary organisms, appear. This type of radish discoloration has

been shown to be inhibited at temperatures below 50° F. It may be

retarded by precooling and cold storage.

(See iÖ,'7^, 75, 76.)

DOWNY MILDEW

See Cabbage, p. 6, and pi. 7, A and B.

WHITE RUST

A/bugo candida (Chev.) O. Kuntze

^Vhite rust is found throughout the world wherever plants of the

mustard family grow. In rare instances it may become of economic

importance in the field, greenhouse, or seedbeds, especially m radish

seedbeds. The disease is of no importance on the market except on

mustard greens or on radishes marketed with the tops. The white

pustules containing powdery spores damage the appearance ot

severely infected leaves.

(See 83.)

19
RUTABAGA AND TURNIP

The turnip is the fleshy taproot and hypocotyl of Brassica rapa,

another member of the mustard family. The rutabaga is Bnissica

napo-brassica. Several horticultural varieties are grown, but in all

of them tenderness, crispness, and freedom from blemishes and decay

are important factors in their marketability.

Young turnips are marketed prepackaged with tops removed and

with tops attached as a bunch vegetable; the late turnip crop and

rutabagas are topped and stored like other root vegetables. Freedom

from blemishes and decay are direct market factors.

ALTERNARíA ROOT ROT AND LEAF SPOT

Alfernaria brassicae (Berk.) Sacc.

The leaf spots of crucifers caused by various species of Altemaria

are in general very much alike. A. hercúlea, however, has been

found to cause a serious decay of turnip roots in the field and in

storage when seasonal conditions are favorable. The fungus may

enter the root through the crown, or infection may take place Avhen

spores and mycelium come in contact with uninjured surfaces of

the root. Bruised and scarred roots are especially susceptible to

infection.

Lesions produced on the roots are usually circular, dark brown,

and firm (pi. 8, C). Frequently concentric rings of light and darkbrown tissues give them a characteristic appearance. Gray to

grayish-brown surface mycelium may form over the decayed areas

in humid storage or pits. Although the dark brown decay may

penetrate deeply into the roots, the decayed tissues remain firm and

are not moist or ill smelling as in the case of bacterial soft rot.

Turnips and rutabagas intended for storage should be carefully

selected for freedom of decay and injuries.

(See 14, 93.)

ANTHRACNOSE

Cof/efofr/chum higgi'ns/anum Sacc.

This disease occurs on many crucifers but is seldom of economic

importance. Turnips, radishes, cabbage, Chinese cabbage, and collards are the most susceptible crops.

In stored turnips, this fungus sometimes causes grayish to lighttan spots with regular depressed margins. Bacterial soft rot usually

follows in these spots and a light-brown, wet decay encircles the

original lesion. Under humid conditions the spores and mycelium

are able to cause infection of uninjured turnip roots. Consequently

this fungus and the associated bacteria common to most soils are

capable of causing considerable damage to storage turnips under

favorable moisture and temperature conditions.

No control measures have been developed.

(See 35.)

BLACK ROT

See Cabbage, p. 5, and pi. 8, A.

BROWN HEART

See Cauliflower, Boron Deficiency, p. 15.

20
CLUBROOT

Plasmodiophora brassicae Wor.

Clubroot occurs on nearly all cultivated crucifers as well as on

many wild species of this family. The malformations that characterize the disease are found only in the parts below ground, with

indirect secondary systemic symptoms. Clubroot is a direct factor

in marketing root crops, such as turnip, rutabaga, and radish.

Although the disease occurs in many regions, it is rarely observed

on the market because the deformed roots are easily sorted out at

packing time.

The outstanding symptom of clubroot is enlargement of the main

or lateral roots or both. At first the club-shaped enlargements are

dirty gray or pale yellow, smooth, and firm; later they become dark

colored. Infected roots are unmarketable.

The causal organism is Plasmodiophora hrrmicae, a soil inhabiting

slime mold. It hibernates in the debris of affected crops or in weeds

of the previous season. For satisfactory control measures in the

held local authorities should be consulted.

DOWNY MILDEW

See Cabbage, p. 6.

GRAY MOLD ROT

See Cabbage, p. 8.

RHIZOCTONIA

See Cabbage, p. 9.

WATERY SOFT ROT

See Cabbage, p. 12, and pi. 8, B.

CUCURBITS

CUCUMBER

Cucumbers are harvested while green. Their desirability depends

chiefly upon their crispness, firmness, shape, and color. The size and

shape of the cucumber fruits vary greatly with different varieties.

For fancy pickles, the pickling varieties are grown and the fruits are

harvested when they reach a length of about 2 inches. The larger

varieties are grown for slicing, for salads, and for keg or barrel

pickles. There is only a limited market for ripe cucumbers. In

general, white or yellowish fruits are looked upon with disfavor,

although occasionally white pickles have been placed upon the market with success.

Certain cucumber diseases occur on both the vines and the fruit

and thus are of direct and indirect effect on the market. The most

important diseases of this type are anthracnose {OoUetotrichum

lagenarium (Pass.) Ell. & Halst.), bacterial spot (angular leaf spot)

{Psevdomonas lachrymans E. F. Sm. & M. K. Bryan), cottony leak

21
{PytMum aphanider?natu7n (Edson) Fitz.), black rot {Mycosphaerella citruUina (C. O. Sm.) Gross), scab {Cladosporium cucumerinum (Ell. & Arth.)), sclerotinia fruit and stem rot (Sclerotmia

sclerotioimm (Lib.) DBy.), sclerotium rot and blight {Pellicularia

rolfsii (Curzi) West), and mosaic, a virus disease.

A number of diseases occur only on the fruits. These are bacterial soft rot {Enoinia spp.), blue mold rot {Pénicillium spp.),

diplodia rot {Diplodia sp., p. 31), fusarium rot {Fusarium spp.),

gray mold rot {Botrytis sp.), pink mold rot {Oephalothecium roseum

Cda.), rhizopus soft rot (Rhizopus spp.), low-temperature breakdown, and sunscald.

(See 4, £7, £8,83,87,101,10^.)

ANTHRACNOSE

CoUetotr'ichum lagenarium (Pass.) Ell. & Hals.

Occurrence and Importance

Anthracnose affects the vines, causing reduced yields due to foliage

and stem injury, and malformed fruit. It also occurs on fruits in

the field ancl in transit, disfiguring them and causing decay, either

directly or indirectly by opening the way for secondary organisms.

Losses are most severe on field crops grown for slicing, or on

cucumbers grown under glass. Damage also tends to be heavy in

fruits that are shipped long distances because of the additional time

for the development of lesions in transit.

Symptoms

On fruits the first symptoms are the appearance of more or less

circular, sunken, watersoaked areas. As the lesions enlarge, the

fungus sporulates abundantly, producing orange-pink slimy spore

masses; later the lesions turn black (pi. 11, C). On mature fruits

the black lesions may show white centers on which old acervuli appear as conspicuous black dots. The tissues underneath are dry and

the sunken epidermis often cracks, exposing the tissues to invasion

by soft rot organisms.

Causal Factors

The causal fungus Colletotrichum lagenarium overwinters in plant

debris of the previous season and on seed from diseased fruit.

Usually the disease does not become general in a field until late in

the season.

The most favorable temperatures for spore germination are between 71° and 80° F. Since the fungus can penetrate the rind of

mature fruit, new lesions develop as long as temperature and moisture conditions are favorable for spore germination. Anthracnose

spots become visible about 5 days after infection. (See Watermelon

Anthracnose, p. 38.)

(See J!^, 8, 31, 36.)

BACTERIAL SOFT ROT

See Muskmelon, Bactrial Soft Eot, p. 28.

22
BACTERIAL SPOT (Angular Leaf Spot)

Pseudomonas lachrymans (E. F. Sm. & M. K. Bryan) Carsner

Occurrence and Importance

Bacterial spot of cucumber occurs on both leaves and fruits in

most humid and semihumid regions. The name "angular leaf spot"

has been applied to the disease as it appears on the leaves. None of

the horticultural varieties now grown is Ivuown to be resistant to this

disease. It does not occur on the watermelon or muskmelon, but

occurs on honeydew melons and squash. Reduction of leaf surface

by severe infection often leads to a reduction in yield. This is the

principal source of loss to the pickle industry, although considerable

loss may result from rotting of small fruits on tlie vines. Wlien

cucumbers are grown for slicing, there is opportunity for development of the lesions on grown fruit.

Symptoms

The fruit lesions, which are at first evident as minute, circular,

watersoaked areas, later become conspicuous because the centers sink

and assume a chalky-white color as a result of the drying out and

cracking of aifected tissues (pi. 10, B and C). Often a gummy

exúdate is formed on the lesions before the spots become dry. The

lesions are usually blemishes confuied to the outer tissues of the

fruits. Frequently, however, as fruits begin to mature, brown lesions

develop in the fleshy tissue beneath the rind, and the discoloration

continues along the vascular system to the seeds. Bacterial soft rot

commonly follows.

Causal Factors

The disease is caused by a bacterial organism, Pseudomonas

lachrymans. The organism is carried on or in the seeds and consequently seedling infection often is the first evidence of the disease

in the field. These bacteria may get on fruit in the field or during

packaging. Since at least 6 days are required for the development

of visfble lesions on fruit after artificial inoculation, fruits showing

young lesions upon arrival at the market may have appeared sound

when picked.

Control Measures

Secure disease-free seed and rotate crops. Refrigerate shipments

to 45 or 50° F. and market promptly.

{See 9, 70, 81, 88,102.)

BLACK ROT (Gummy Stem Blight)

Mycosphaere/Zo citrullina (C. O. Sm.) Gross

Black rot is an important decay in cucumber shipments from

Florida, other Southern States, and Cuba. Inconspicuous watersoaked spots on which patches of white, cottony mycelium are growm<r mark the first appearance of the disease on the fruit (pi. 11, A).

Later these areas gradually darken and eventually black fruiting

bodies of the ñuigus (both pycnidia and perithecia) may be seen

(pi 11, B). Although the decay may continue to develop during

transit, there are no indications that new lesions appear after the

23
cucumbers are harvested. Initial infections that are not observed at

packin«; time apparently account for the decay found on the market.

(See Watermelon Black Rot.)

(See 12, 13, 100.)

COTTONY LEAK

Pythium aphanidermafum (Edson) Fitz.

Occurrence and Importance

Cottony leak has been reported from only a few localities in the

Southeastern States. Infection of cucumber and squash fruits take

place in the field, and decay develops and spreads very rapidly during transit. Tlie fungus is spread by contact, and visible wounds

are apparently not necessary to enable it to penetrate the fruits. The

fungus also causes damping-off and a vine canker during excessively wet seasons.

Symptoms

The first symptoms on the fruits are soft, dark green, watersoaked

lesions; later, as the mycelium penetrates the tissues of the fruit,

Avater is liberated in large quantities. In the moderately humid

atmosphere of containers during transit, a very luxuriant, white,

cottony mycelium is produced, which sometimes completely covers

the fruit (pi. 11, D). When juice from decaying cucumbers leaks

down upon those below, the mycelium becomes flattened and forms

a matted layer over the surface of the fruits.

Causal Factors

The causal fungus, Pythium aphanidervuttum, is a soil inhabitant.

It causes greatest damage in wet soils. This fungus produces no

aerial spores, but depends upon propagation by mycelium and by

spores that swim about in water during the rainy season. Fruits

that come in contact with the infected soil or that become spattered

with rain and soil containing spores or mycelium of Pythium, are

consequently liable to infection.

Control Measures

This disease may be reduced by providing good drainage. No

cucumbers that show evidence of decay should be shipped.

(Seeg^.)

LOW TEMPERATURE BREAKDOWN

Cucumbers held for one week or longer at temperatures of 32° to

40° F. are subject to low-temperature breakdown soon after they are

removed from storage. This injury is recognized by the presence of

numerous sunken spots over the surface of the fruits (pi. 10, A), the

total area of which may cover half to three-quarters of the cucumber

surface. Frequently the tissues immediately at the base of the spines

are first affected; likewise those about the lenticels appear to be involved in most cases. The sunken areas soon become spotted with

molds ^ and affected with shallow decays caused by species of

Fuaarium and other fungi.

If the cucumbers are held at 50° F. and 75 to 95 percent relative

humidity, little or no breakdown develops, but they tend to ripen

rather rapidly, the color changing from green to yellow, and there

24
may be some shriveling and surface pitting. Chilling at lower temperatures depends on how low the temperatui-e is and the length of

exposure. Slight injury occurs in 4 days at 32° and 8 days at 41°.

Severe injury occurs after 12 days at 32° and IG days at 41°

(See Ù, 51.)

MOSAIC

Mosaic is a serious disease in the production of cucumber, muskmelon, squash and pumpkin. Infected vines are mottled, stunted and

often killed and the yield of fruit reduced. Tlie cucumber fruit is

mottled, misshaped, warty, and stunted. It is usually unfit for sale

although, occasionally, slightly affected fruit may be found on the

market. Summer Straightneck squash are often mottled green and

yellow, but other kinds of squash, pumpkin and muskmelon fruits

show little evidence of disease except for reduction in size and poor

quality.

Mosaic is caused by a number of viruses that occur in the growing

plants and are transmitted by insects and by handling the plants

during cultivation and picking.

The disease does not spread after harvest. Diseased fruits are not

attractive and should not be packed for marketing.

(See 23.)

SCAB

C/acfosporium cucumerinum Ell. & Arth.

Scab, an important disease of cucumbers, also occurs on pumpkin,

squash, and muskmelon. On cucumbers it is of chief importance on

the greenhouse crop and on the pickle crop in the North Central

States.

The cause of the disease is a fungus, Cl<idos'porium cucumerinwin.

It overwinters on plant debris in the soil. It occurs on the leaves

and stems but it is on the fruits that the chief injury occurs. Small,

grayish, slightly sunken spots mark the first appearance of the disease there. Frequently a gummy exúdate forms on the lesions and

later turns dark. Under dry conditions the lesions may remain as

more or less superficial blemishes; under humid conditions, however,

the fungus causes a shallow decay. In later stages the decayed

tissues become covered with a dark olive-green layer composed of the

mycelium and spores of the causal fungus.

The disease is favored by cool, moist weather, inasmuch as the

pathogen grows best at about 70° F. and develops slowly at 95°. It

is particularly severe under humid conditions. Lesions apparent at

the time of shipping may continue to develop during transit, but

no new lesions develop.

Control Measures

The planting of resistant varieties is most effective in controlling

this disease.

(See 22, 82, 86.)

SOIL ROT

Rhizoctonia (Pe///cu/aria filamentosa (Pat.) Rogers)

Soil rot of cucumber fruits was first reported in th^ 1949 crop in

North Carolina. Very small cucumbers showed yellowish-brown

superficial discoloration whereas the larger fruits had a rather firm,

25
dark, watersocaked decay. Under humid conditions a dense mold

covered the infected fruits within 2-Í hours. In inoculation tests at

7G° to 87° F. the first symptoms of infection were evident in 24

hours and the fruits were almost completely rotted in 72 hours. This

decay profiressed most rapidly at about 82° F. or above.

Since this fungus is in the soil and may attack several other vegetable crops it is difficult to control this disease. Temperatures near

50° F. sliould retard its deve]oi)ment during transit and marketing.

(See 28.)

MUSKMELON

The muskmelon, Cucumls melo L., is one of the many species belonging to the gourd family, the Cucurbitaceae. There are several

botanical varieties within the species. Although some of the forms

are not actually musk-scented, all members of the species are referred

to as muskmelons. The term "cantaloup" commercially is used

synonymously with muskmelon. Although not botanically correct,

cantaloup will be used in this publication to denote the small greenskinned, netted melons that are the most important single type of

muskmelon found on the American market. Other types of muskmelon in the approximate order of their importance are : honeydew

melon, honeyball melon, persian melon, casaba melon, Spanish melon,

and santa claus melon.

The market value of these fruits depends upon their flavor and

freedom from blemishes and decay. The flavor depends primarily

upon the variety and tlie stage of maturity at which the fruit is

harvested. In order to reach the market in an acceptable condition

the melons must be picked while still firm, yet if they are removed

from the vine too soon they lack flavor.

( See 5,50,51,57,87,95,96,98.)

ALTERNARíA ROT

Alternana tenuis Nees

Occurrence and Importance

Alternarla fruit rot is of general occurrence in the market and in

storage on all types of muskmelons. It may occur in melons from

any region. Much of the mold at the stem scar and elsewhere on

cantaloups is Alternaria. "Wlien the rot occurs on honeydew and

honeyball melons, it seriously detracts from their appearance even

when only small areas of the melon surface are involved. Decay by

other rot-producing organisms frequently follows alternaria rot.

Symptoms

On honeydew and honeyball melons, alternaria rot causes circular

or oval brown to black sunken lesions, some of which may be as large

as 21/2 inches in diameter. The edges of the lesions are fairly regular

and definite and occasionally are slightly watersoaked. Frequently

there are alternating bands of lighter and darker colors on the surface of the lesions that form a pattern of concentric rings. The

lesions become darker as they grow older and finally become definitely black. The lesions usually are covered by a deep grayish-olive

colored fluffy mat of the fungus, or by scant mycelial growth covered

by a black, thin, velvety layer of sporulating hyphae (pi. 13, A).

26
The decay is often largely confined to the rind. Sometimes the

decay is moist and progresses well into the flesh. In both cases the

boundaries are sharply delineated and the decayed tissues can be

easily lifted out. The color of the diseased tissue varies from "ravish white to nearly black. ^ -^

The internal symptoms on cantaloups are similar to those on

honeydew melons. The external ones are more or less definite lesions

covered with dark sporulating fungus mycelium. They resemble the

late stages of cladosporium rot (p. 30) and often cannot be distinguished from the latter without microscopic examination.

Causal Factors

This disease may be caused by several strains or species of alternaría. Some studies indicate that Altemaria tenuis Nees is one

species that causes rot in melons.

Optimum growth in culture of alternaria isolates from muskmelons occurs at 75° to 86° F. Only slight growth occurs at 37°

The optimum temperature for development of decay in inoculated

honeydew melons was 75° to 80°. Although no decay develops at

37 in 10 days, lesions slightly over 14 inch in diameter were produced m 4 weeks.

Altemaria rot frequently follows sun scald injury, low-temperature

breakdown, and skin breafa and cracks.

Control Measures

Alternaria rot is best controlled by the grading out of melons that

have been injured by sunburn, by careftil handling to avoid skin

breaks and cracks, and refrigeration (35° to 40° F. for cantaloups

and 45° to 50° for honeydews) in transit.

(See 95, 96.)

ANTHRACNOSE

Colletotricbum lagenarium Ell. & Hals.

Occurrence and Importance

This disease is seldom seen on muskmelons of any kind on the

market. However, an occasional shipment of honeydew melons may

be affected, "^^-lien this occurs, the affected melons are unsalable or

at least lower in market value. Besides affecting the appearance of

the fruit, the flesh bordering the decayed spots has a disagreeable

taste.

Symptoms

Anthracnose causes circular or oval spots that are about 14 to %

inch in diameter. They are shallow at first, but soon become sharply

sunken. Salmon-colored or pink spore masses often arranged in

concentric lings are produced in abundance over the surface of the

larger lesions (pi. 12). Later the lesions become dark colored and

the decay penetrates deeply into the flesh. Other decay frequently

starts in the anthracnose lesions.

Causal Factors

Anthracnose is caused by the fungus Colletotnchum lagenarium.

It causes a serious disease of the vines and foliage of muskmelons

and other cucurbits in the field and when conditions are favorable

27
the fruit becomes infected. In Colorado it was found that honeydew

melons became infected by washing in water that was contaminated

with spores from diseased melons. Some experimental work indicates that wounding is necessary for infection to take place. Melons

that become infected in the field may appear sound when harvested

but be badly infected within 5 days if conditions are favorable for

development of the disease.

The optimum temperature for germination of the spores and

growth of the fungus is generally considered to be about 75° F., but

good growth takes place between 65° and 85°. Growth drops off

rapidly at temperatures above 85° and there is none at 95° or higher.

Growth in 6 days at 55° is less than half as great as that at 65°

and none occurs at 45°. Only a trace of growth occurs in 2 weeks

at 45°.

Control Measures

Avoid shipping melons from fields affected with anthracnose. Refrigerate promptly and keep transit temperatures between 45° and

50° F. to prevent development of anthracnose of honeydew melons

in transit. Use water containing 1,500 p.p.m. chlorine in the wash

tank to prevent infection during washing.

(See Iß, Iß, 95.)

BACTERIAL SOFT ROT

Erwinia spp.

Occurrence and Importance

Bacterial soft rot is found only occasionally on domestic muskmelons, as a stem end rot and following injuries, but it causes considerable loss every year on shipments of honeydew melons from

Chile. Cucumbers, squash, and pumpkins are also seriously damaged by this disease.

Symptoms

The early symptoms of this decay are watersoaking and a pronounced softening of the flesh about the point of infection. As the

decay advances, the infected fruits become soft and mushy. Eventually they become hollow shells filled with liquefied, broken down

tissues. The skin may remain unbroken at first, but finally tears

and collapses as the watery disintegrated tissues and seeds spill out.

The decay is usually accompanied by an offensive odor.

Causal Factors

Bacterial soft rot of muskmelons has been attributed to Erwinia

aroideae (Towns.) Holland, and E. carotovora (L. R. Jones) Holland. The optimum temperature for decay development by soft rot

producing bacteria isolated from Chilean honeydew melons is between 80° and 85° F. At this temperature infected melons are almost completely rotted in 3 days. Decay is restricted at 90° and

only a trace occurs at 98°. The rate of decay falls off rapidly at

temperatures below 80°. Only a trace of decay occurs in 2 weeks

at 45°.

28
Control Measures

Careful handling to prevent injuries and refrifjeration at 35° to

40° F. will help prevent development of soft rot of cantaloups during transit and marketing.

(See 95.)

BACTERIAL SPOT

Pseudomonas lachtYmans (E. F. Sm. & M. K. Bryan) Carsner

Occurrence and Importance

This disease on honeydew melons was first observed at Chicago in

1940 in a shipment from Colorado. It was found again at Chicago

in 1944 in a car from Colorado in which 40 percent of the melons

were aflFected over 10 to 75 percent of their surface area. In 1945

it was also found on melons from Arizona.

Symptoms

This disease causes slightly sunken, circular to oblong, watersoaked, greenish-tan spots that are % to 14 inch in diameter (pi.

13, B). Some of the spots coalesce to form large brown or black

areas. The bacteria apparently pass through the stomata into the

parenchyma cells underneath. Bacterial spot becomes visible 5 to 8

days after inoculation.

Causal Factors

Bacterial spot is caused by Pseudomonas lachrymans, the same

organism that causes angular leaf spot of cucumbers. (See p. 23.)

The optimum temperature for growth of the organism in culture is

77° to 80° F., the minimum about 35° and the maximum 95°.

Control Measures

Control measures used with the growing crop should reduce the

chances of infection. Transit temperatures of 45° to 50° F. should

retard development of the disease in honeydew melons enroute to

the market.

(See 71.)

BLUE MOLD ROT

Pénicillium spp.

Occurrence and Importance

Blue mold rot is often found on cantaloups and honeyball and

honeydew melons on the market but ordinarily it does not cause

appreciable loss. It is usually found on honeydew melons that have

been held in cold storage or on the track for some time. The disease

gives the flesh a musty odor and taste.

Symptoms

The lesions caused by blue mold are usually restricted, well-defined

spots, circular to oval and 1/0 to 2 inches in diameter The surface

0Î the spots is somewhat darker than the normal rind and slightly

depressed. Underneath, the diseased tissues are sharply dehneated

from the healthy tissues. Spore masses that are bluish or greenish

in color develop abundantly along skin cracks that are found over

the lesions and over the inner surfaces of cavities m the ñesli.

Vi
Causal Factors

The blue mold rot that is most commonly observed is caused by

slow-frrowin^ species of Pénicillium. Occasionally rapid-growing

species have been observed. The optimum temperature for growth

of the slow-growing species in culture is between 65° and 75° F.

No growth occurs in G days at 32° or 90°.

Control Measures

Blue mold rot can be controlled best by refrigeration at 45° to

50° F. and by prompt movement of melons in transit and after

arrival at the terminal markets.

(See 95.)

CHARCOAL ROT

Macrophom/na phaseoili (Maub.) Ashby

Occurrence and Importance

Charcoal rot is frequently found in shipments of honeydew melons

from South America, but is seldom found on domestic melons.

Symptoms

In the early stages charcoal rot causes a gray or purplish-gray

watersoaked spot. It enlarges rapidly and may eventually cover the

whole melon. As the decay advances, a thin wrinkled crust of black,

tightly j^acked, minute sclerotia is formed over the surface of the

lesion. The crust is easily peeled off to expose the watersoaked, but

more or less normal colored, infected flesh beneath. The infected

areas are soft and spongy, and unless invaded by soft rot organisms

they dry out to form black wrinkled mummies. The flesh of diseased melons has a pungent sour odor and taste.

Causal Factors

Charcoal rot is caused by Macrophomina phaseoK {Sclerotium

bataticola), a fungus that has long been known as the cause of charcoal rot of sweetpotatoes. Growth of the fungus in culture and development of decay are most rapid at about 90° F. The maximum

temperature is about 110° and the minimum about 50°. Lesions

3 inches in diameter were developed in 5 days at 85° F., but no

decay developed in 2 weeks at either 45° or 50°. Wounding is

necessary for infection.

Control Measures

Transit temperatures below 50° F. and careful handling to avoid

injuries should give effective control of charcoal rot.

(See 95.)

CLADOSPORiUM ROT

C/adospor/um cxjcumerlnum Ell. & Arth.

Occurrence and Importance

Cladosporium rot, also called green mold rot, occurs frequently on

cantaloups and honeyball and honeydew melons on the market. It

seriously detracts from the appearance of the melons and decreases

the selling price. This disease is especially important on melons

that have been held for some time in the car or in cold storage.

30
Symptoms

Cladosporium rot commonly affects cantaloups at the stem scar

and causes the so-called slip rot. It also occurs at cracks and other

points over the surface. The surface of the affected areas is covered

by a thin superficial layer of mold that is deep olive green in color

at first and later turns black (pi. 16, A). The netting is frayed and

dirty looking, when partially covered with mold. The edges of the

lesion are indefinite and irregular. The diseased rind is fairly firm

and moist and the tissues i/ic to %Q inch beneath are soft and spongy.

Honeyball melons also are affected by Cladosporium rot at the

stem scar and elsewhere on the surface. It occurs especially along

the shallow irregular surface cracks. The mold spots that are scattered over the surface of the melon may have indefinite fimbriated

edges or definite lesions as occur on honeydew melons.

The cladosporium rot lesions on honeydew melons vary from small

specks to spots 1 inch or more in diameter that sometimes coalesce

and form larger diseased areas. The individual spots are circular

to oval and have fairly regular and distinct margins. The lesions

are smooth, shiny, and black but are frequently surrounded by a

narrow, light buff-colored band. Under humid conditions a heavily

sporulating mat of green or greenish-black mold develops over the

affected areas. Decay is confined chiefly to the rind or tissues immediately beneath the rind. The affected tissues may dry out and

become papery, if not invaded by secondary organisms.

Causal Factors

This disease is caused by the fungus Cladosporium cucumerinum.

The optimum temperature for growth in culture is about 70° F. No

growth occurs at 90° in 6 days. The minimum temperature for

arowth is near 35°. Cladosporium rot occurred on cantaloups after

1 week of storage at 40° to 42° and after 2 weeks at 32° to 34°.

Severe spotting has developed on honeydew melons after 2 weeks'

storage at 40° to 42°. Growth of this fungus is favored by condensation of moisture on the melons.

Control Measures

Cladosporium rot appears to be of greatest importance in poorly

refrigerated shipments and in lots that are not handled promptly

at the market. T j. • ..• *. AC\O T? Avoiding delays in handlmg the melons and refrigeration at 40 -b .

or lower will reduce the amount of cladosporium rot.

(See 95.)

DIPLODIA ROT

D\p\odi\a naialensis Pole-Evans

Diplodia rot has been reported as a field decay of cantaloup and

cucumber fruits in Texas. Diplodia stem end rot has long been

reco^ized as a serious decay ofVatermelons (see Watermelon Stem

^Undei market conditions diplodia rot is found only on l^oneydew

melons from South America. It is characterized by a bleaching of

Se skin an^ the development of buff-colored lesions that may occur

anywhere over the surface of the melons, but^rarely at the stem end

Usullly ihere is only one lesion on a melon, but by enlargement this

31

553801°—61 3
may eventually cover most of the melon surface. In later stages

the lesion becomes black in the center, the dark color finally spreading outward over most of the lesion. The decayed tissues are

spongy and somewhat softened and have a pungent sour odor and

taste, but the melon retains its normal shape. In later stages the

decay, occurring as it does under the same conditions as those in

which charcoal rot is found, may be mistaken for the latter. It is

distinguishable, however, by the development of a greenish-black

stroma beneath the epidermis which later turns black. The coarse

black fruiting bodies of the causal organism develop in profusion

over it and rupture the epidermis which peels back and curls up.

The causal organism and the decay produced by it develop most

rapidly between 85° and 90° F. The maximum temperature lies

near 100°, and the minimum between 45° and 50°.

The disease can be held in check during transit by temperatures of

50° F. or lower. As a further measure of control all mechanical

injury should be avoided during picking and packing. (See 96.)

FUSARIUM ROT

Fusarium spp.

Occurrence and Importance

Fusarium rot is one of the most common diseases of muskmelons

on the market. It is found on cantaloups, honeyball, honeydew,

Persian, Spanish, casaba, and other melons. It is of most importance

on fully ripe melons. Although on domestic melons the lesions may

occur anywhere over the surface, on honeydew melons from South

America the disease is found chiefly as a stem-end decay.

Symptoms

On green-skinned varieties of melons, fusarium rot frequently

occurs as small scattei-ed lesions of varying size and shape, with

numerous small lesions commonly coalescing to form large diseased

areas. The most conspicuous external and internal symptom is the

development of the white or pinkish-white mycelium of the causal

organism. Upon cutting the melon open the diseased tissues are

delineated spongy bodies that can easily be lifted out intact from

the healthy flesh. They may either be confined to the outer tissues

of the melon inxmediately beneath the rind or they may extend to

the seed cavity (pi. 14).

On the white-skinned varieties the lesions are brown at first and

form more sharply defined spots than on the green-skinned varieties. They likewise later become covered with white or pinkishwhite mold. The internal symptoms are similar to those on the

green-skinned varieties. Occasionally the purplish-red discoloration

produced by Fusarium scirpi var. (wuminatum (and certain other

species) is evident even before cutting the melon. The decay produced by this species is further characterized by the extremely bitter

taste of the infected tissues.

Causal Factors

The symptoms produced by the various species are strikingly similar with the following exceptions : Fusarium scirpi Lamb. & Fautr

var. acumtnatum (Ell. & Ev.) Wr. produces a purplish-red discolo32
ration of the diseased flesh, whicli has a very bitter taste; F. culmomm (W.G. Sm.) Sacc, F. graminium Cda, and F. monilifo-nne

Sheld. var. subgluttnans Wr. & Reink. produce some reddish discoloration but do not produce the bitter flavor.

The temperature relations of the various species are also similar,

most of them having optimum temperatures of either 75° or 80° F.

The average diameter of lesions did not exceed % inch after 1 week

at 65°, or % inch after 3 weeks at 45°. Only a trace of decay

occurred after 2 weeks at 35°.

Control Measures

The most important methods for controlling fusarium rot are the

avoidance of wounds during picking and packing, good refrigeration in transit, and prompt handling of the melons after their arrival

on the market.

(See 95.)

LOW TEMPERATURE BREAKDOWN

Muskmelons, particularly honeydew melons, stored for 2 weeks or

longer at 32° to 34° F. (or, under certain conditions, even at higher

temperatures), before shipment or after their arrival on the eastern

markets, frequently become affected with low temperature breakdown. There may be no evidence of injury to the melons at the

time of their removal from the car or there may be an irregular

watersoaking of the rind. After the melons have been removed

from stoi-age and held at room temperatures for a day the typical

symptoms develop. The injury is first manifested by watersoaking

of the rind which may be restricted to limited areas of irregular

size and shape, or it may extend over half or more of the melon

surface. The juices of the melon exude and the skin becomes sticky.

There is a gradual softening of the melon although the tissues retain their general form and structure. The affected rind may eventually become drab gray or somewhat brown.

Low-temperature breakdown is usually quickly followed by various decays including chiefly alternaria rot (pi. 11, F), blue mold

rot, cladosporium rot, and fusarium rot. Melons stored for any

considerable length of time may be subject to this type of injury.

Transit temperatures of 45° to 50° F. are recommended for honeydew melons.

(See 96.)

PHYTOPHTHORA ROT

Phytophthora spp.

Occurrence and Importance

Phytophthora rot of honeydew melons is frequently responsible

for appreciable losses in the shipments from South America. Ordinarily it is of minor importance on domestic muskmelons, occurring chiefly on a few individuals scattered through occasional carlots originating in Colorado and California. On several occasions,

however, the disease has been responsible for the loss of practically

the entire contents of the car.

Symptoms

The decay may occur in the form of one or several slightly sunken

spots of practically normal color except for a limiting border of

33
reddish brown. Generally, however, it is recognized_ by the presence of an irre^lar bleached area of the rind that is not sunken

nor well defined in extent. As the lesion enlarges the affected

flesh becomes slightly softer and more spongy than normal. This

and the slight bleaching are the only external evidence of the disease.

The affected area of the melon later becomes somewhat watersoaked under pressure. The epidennis loosens, forms blisters,

and is easily torn away. As the lesion enlarges, covering most

of the surface, the fruit shrivels, the rind wrinkles and folds, and

the melon flattens out somewhat under its own weight. Under humid conditions a wet appressed dirty white felty mycelial growth

covers the lesion (pi. 15, A). Diseased flesh, although practically

normal in color, is slightly sour. When afi'ected flesh is pressed

between the fingers the juice is squeezed out, leaving a felty residue

of fungus mycelium which has formed in abundance.

Causal Factors

It has not been determined whether more than one species of

Phytophthora is responsible for this decay. Artificial inoculations

with several different species have produced identical symptorns.

The temperature relations of the isolates obtained from widely different sources were very similar. All grew most rapidly and produced decay most abunclantly at 80° to 85° F. The maximum temperature was between 95° and 100° and the minimum somewhat

below 50°. The fungus is soil borne and infects the melons while

they are still attached to the vines. The exact conditions under

which extensive infection occurs in the field have not been determined.

Control Measures

Until more is known regarding the conditions favoring infection

the only control measure that can be recommended is that of maintaining transit temperatures of 50° F. or lower.

(See 77, 95, 97.)

PINK MOLD ROT

Cephalothedum roseum Cda.

Pink mold rot caused by the fungus CepTialotTiecium roseum is

found on the market occasionally on cantaloups and Spanish melons

and more frequently on honeydew melons. It is an important decay

only in shipments of honeydew melons from South America. The

decay is also occasionally seen on cucumbers.

The earliest symptom of pink mold rot on honeydew melons is a

brown discoloration of the rind. Lesions vary from small spots 1

inch in diameter to large areas covering one-third of the melon

surface. Frequently these occur at the stem end (pi. 15, B) ; later

the lesion becomes covered with the mycelium and the abundant

pink spore masses of the causal fungus. The decay at times resembles some of the fusarium rots but can easily be distinguished

from them by the extremely bitter taste of the affected flesh.

The causal organism grows most rapidly at a temiDerature of about

70° F. The highest temperature at which growth is made is somewhat above 95° ; the lowest somewhat above 40°. Control measures

therefore include good refrigeration in transit.

(See 95.)

34
RHIZOPUS SOFT ROT

Rhizopus sfolonifer (Fr.) Ehr., and other Rhizopus spp.

Occurrence and Importance

Rhizopus soft rot is common on all types of muskmelons, cucumbers, squash, and pumpkins found on the market. It is also found

on watermelons (pi. 22, B). It is a rapidly developing and destructive

decay. The earliest symptoms are softening and pronounced watersoakmg of the flesh. As the lesions enlarge the affected flesh is readily

flattened by the weight of the melon or pushed in by adjacent melons

m the container. Nevertheless, it holds together, and the affected

flesh is never completely disintegrated and soupy as is that of melons

affected with bacterial soft rot. The skin may be torn or remain

unbroken for some time. There is often no external evidence of the

causal organism, although frequently a slight development of mycelium may occur here and there on the lesion. Internally the

decay_ is recognized by the soft watersoaked flesh that is sharply

delimited from the healthy tissue and can usually be removed intact (pi. 16, B). It has a slightly sour odor and taste. The coarse

mycelium of the causal organism can be demonstrated by gently

pulling apart the diseased tissue.

The decay on cumbers, squash (pi. 19), pumpkins, and watermelons is similar to the decay of muskmelons.

Causal Factors

Rhisopus stolonifer has generally been assumed to be the cause of

the decay of cucurbits and other vegetables. HoAvever, it has been

shown by artificial inoculation that a number of different species

of Rhizopus are capable of producing a decay of cantaloups, cucumbers, squash, and watermelons. Studies of a large number of isolates from muskmelons indicate that about half of them belong to

the medium-temperature group typified by R. stolonifer and the

other half to the high-temperature group. R. arrhisus has been

reported from pumpkin.

The spores of Rhizopus are widely distributed in the soil, water,

and air; consequently infection may occur at any time. Wounds of

some sort appear to be essential for the entrance of the organism.

The loss is usually greater on the riper melons. The temperature

requirements differ considerably with the différent species. For

Rhizopus stolonifer and others of the medium-temperature group,

growth on artificial media is greatest at 70° to 85° F. ^ Those isolated from decaying honeydew melons grew most rapidly in culture and caused' decay in melons most rapidly at 80° F. Those

species of the high-temperature group are most active at 85° to

95° F.

Control Measures

The chief methods of controlling rhizopus soft rot are the avoidance of bruising and injuring melons during picking and packing.

The use of refrigeration (40° F. or lower) in transit is recommended for cantaloups. Prompt handling of the products upon

their arrival at the terminal markets is also desirable.

(See H, 95.)

35
PUMPKINS

The pumpkin is the large, globular, or oblong fruit of the pumpkin

plant {Cucúrbita pepo L.). The marketability of pumpkins depends upon their color, maturity, and freedom from decay.

Fusanum rot and rhizopus soft rot are about the only important transit and market diseases of pumpkins. These and other

diseases that occasionally occur are similar to those of squash (see

Squash, p. 36).

(See i, 2, 78, 79.)

SQUASH

The term squash is loosely applied to the fruit of various members of the gourd family, but is not limited to any one species.

The summer squashes are fruits of Cucúrbita pepo and the winter

squashes are fruits of other species {C. maxima Duch.). The summer squashes are eaten while the rind is still soft; consequently,

more careful handling is required for those fruits than for the

varieties not harvested until the rinds have become mature and

hard. The marketability of all varieties depends upon freedom

from bruising and disease.

Among the market diseases of the summer types of squash the

following are sometimes of considerable importance : bacterial soft

rot {Erioinia spp.), blossom end rot {Choanephora cucurbitarum,

(Berk. & Rav.) Thaxt.), cottony leak {Pythium spp.), fusarium rot

{Fusarium spp.) (pi. 11, E), phytophthora rot [Phytophthora

spp.), and rhizopus soft rot {Rhizopus stolonifer) (pi. 19).

The winter or storage types of squash suffer most loss from alternarla rot {AUernari-a tenuis Auct.), black rot {Mycosphaerella citrullina (C. O. Sm.) Gross), fusarium rot {Fusarium spp.), rhizopus

soft rot {Rhizopus spp.), and scab {Cladosporium, cucumerinum

(Ell. & Arth.)). Sometimes gray mold rot {Botrytis cinérea

(Pers.) ), and watery soft rot {Sclerotinia sclerotioi^wm (Lib.) DBy.)

cause serious damage.

There are some serious discolorations of the rinds of squash, the

cause of which has never been determined. No decay is associated

with these blemishes. The so-called pox, zonate spots, and spiderweb discolorations apparently do not harbor any organisms that

can be cultured.

(See 7, 18, 33, IfS, 53, 58, 105.)

ALTERNARíA ROT

Alternaría tenuis Auct.

Altemaria rot is a major disease of squash in cool, damp storages

It is especially serious in lots of squash that have been injured by

low temperature, although no freezing has occurred (pi. 17, B).

Inconspicuous field infections or spores on the fruit may germinate

and cause spots \i to 1 inch in diameter during storage. At first

the lesions are somewhat tan and smooth, but mider humid storage

conditions a greenish-black mold appears over the surface (pi. 17,

B). In hardshell varieties the ñmgus penetrates in the flesh, pro36
f^t'^ä pockets of decay i/o inch or more deep. These decay pockets

^/o ' 7L\^^^ yellowish to black and are fairly dry and spongy.

BACTERIAL SOFT ROT

See Muskmelon, Bacterial soft rot, p. 28.

BLACK ROT (GUMMY STEM BLIGHT)

MycosphaereUa dtrullina (C. O. Sm.) Gross

Black rot is the cause of extensive damage to storage lots of

squash Infections of the fruit occur in the field at the stem end

and sides of the fruits. At first the lesions produced are watersoaked and greenish brown in the acorn types, but soon become

tirm and black as fruiting bodies (pycnidia) are formed in great

numbers (pi. 17, A and 18, A). Hard, dry, black lesions dStted

with minute black pycnidia characterize this disease on storao-e

squash. (See Black Rot of cucumbers, p. 23, and melons, p. 39 ) '^

(See 33.)

BLOSSOM END ROT

Choanephora cucurb'itarum (Berk. & Rav.) Thaxt.

Occurrence and Importance

This disease seems to be of importance only upon the squash,

but_ It has been observed on the flowers of cucumber, althea, scarlet

hibiscus, okra, cotton, and a few other plants. Blighting of the

squash blossoms and subsequent decay of the fruits take considerable toll m the market garden districts. Although a fruit rot is

produced in the field, apparently few affected fruits are shipped

to market.

Symptoms

The attack on the flowers is usually evident the second day after

they open. The fading blossoms are covered with a dense growth

of immature, white spore-bearing structures of the fungus that

change to brown and finally purplish black at maturity. From

the flower the mycelium works down into the newly forming fruits

and causes decay. Wlien larger fruits become affected at the blossom end, a rapidly progressing, soft, wet rot is produced. Half

of a moderate-sized fruit may rot within 15 to 20 hours. A profusion of black sporangia develops on the decaying fruit, giving

it a very characteristic appearance.

Causal Factors

The causal fungus, Choanephora cucurbitarum^ looks like Rhizopus when fruiting, but the absence of coarse, whiskerlike mycelium

serves to distinguish it from that fungus. The spores are disseminated by insects, rain, and wind. Thick-walled spores (zy^ospores)

on the surface or within decaying plant tissue enable the fungus to

withstand drought and extremes of temperature. The fungus causes

greatest damage in seasons of high humidity and excessive rainfall.

Control Measures

Infected fruit should not be packed for shipment.

(See 103.)

37
COTTONY LEAK

See pi. 11, D, and Cucumber Cottony I^eak, p. 24.

FUSARIUM ROT

See pi. 11, E, and Fusarium rot of muskmelon, p. 32.

PHYTOPHTHORA ROT

See pi. 18, C, and Watermelon Phytophtliora Rot, p. 41.

RHIZOPUS ROT

See Muskmelons, p. 35, and pi. 19.

SCAB

See Cucumber Scab, p. 25.

WATERMELON

The watermelon {Oitrulhis vulgaris Sclirad.) is a member of the

gourd family {Cucurhitaceae). Its marketability depends upon size,

shape, color, and freedom from blemishes and decay.

Like other plants belonging to the gourd family some diseases of

watermelons occur both on the vines and the fruits. These are

anthracnose {Oolletotrichum lagenariwn (Pass.) Ell. & Hals.),

black rot {Mycos-phaerella citi^Uina (CO. Sm.) Gross.), sclerotium

rot {Pellicularia rolfsii (Curzi.) "West), and soil rot {PeUicuhxria

filamentosa (Pat.) Rogers).

The following diseases occur primarily on the fruits either in the

field or after they are harvested and consequently are diseases of

importance in transit and on the terminal markets: Bacterial soft

rot (p. 28), blossom end rot, charcoal rot {Macropliomina fhaseoli

(Maub.) Ashbj'), fusarium rot {Fusariiinn spp.), pythium rot

{Pythhim spp.), phytophtliora rot {Phytophtliora spp.), rhizopus

soft rot (pi. 22, B), and stem end rot {Diplodia sp.).

(See 5, k6, 66, 91)

ANTHRACNOSE

Co//efofncfium lagenar'ium (Pass.) Ell. & Hals.

Occurrence and Importance

Anthracnose is often the most serious of all field diseases of the

watermelon and is more important on that crop than on either

cucumber or muskmelon. This is in part due to the fact that the

fruits must remain in the field a long time and that individual

fruits have great value. The disease occurs on the vines and the

immature fruits, causing reduced yield, and on the mature fruits,

disfiguring them and causing rot.

Symptoms

On older fruit, the disease is recognized by the presence of slightly

elevated pimples Avith yellow translucent centers. On mature fruit

the nailhead type of lesion is very common (pi. 21, B). These are

small, circular, raised welts on the rind, which are dark green. As

38
tliey increase in size the centers turn Ijrown and become sunken,

and under moist conditions the pink acenaili of the fungus are

formed in which sticlcy masses of pink spores are produced (pi. 20,

A). As the lesion enlarges the surface cracks, exposing either the

rotted tissue or a cavity underneath. The fungus causes a rather

slowly advancing dry rot of the rind and finally penetrates the pulp.

Frequently a halo of lesions develops around tlie bottom surface that

is in contact vrith the soil. These lesions often become black and

corky. It is this kind of infection which leads to rotting in the

field. Under extremely dry, hot conditions, during the melon

harvest, the lesions may remain in the blister or nailhead stage.

The disease develops and spreads in transit, since the fungus is

able to lie dormant in the melon rind and to develop visible lesions

when moisture and temperature conditions become favorable.

The causal fungus is the same as that on cucumbers and muskmelons (see pp. 22 and 27).

Control Measures

Control measures of local authorities should be followed, since

the seriousness of this disease varies with climatic conditions and

the varieties grown. Watermelons suspected of being infected should

not be shipped.

(See ^, Go.)

BLACK ROT

A1ycosphaere//a cHruHina (C. O. Sm.) Gross

Occurrence and Importance

In recent years black rot of watermelons has been a serious disease

on the market. INIost serious trouble has been encountered in shipments of melons from Florida and Iowa. In some cars more tlian

50 percent of the melons have been infected. Buyers refuse to purchase melons showing black rot, even in the early stages, unless they

are given a large discount.

Symptoms

IMelons arriving on the market show definitely outlined greenishtan to black spoTs Vo inch to 2i/o inches in diameter (pi. 20, B).

Lesions have black ce'nters in which small black specks mdicate the

development of fruiting bodies (pycnidia). There is usually little

if any surface mold. The spots remain smooth and moderately firm

until they get quite large. The larger lesions often show brownishblack concentric zones. The decay eventually penetrates the rmd

and involves the flesli of the melon. Secondary mfections by bacteria and yeasts sometimes cause a soft, foul-smelling decay.

Causal Factors

Black rot of melons, cucumbers, and squash is caused by the fungus

MyrosphaereUa citrulliru,. It causes most damage m the Southern

States but has been found as far north as Wisconsin. The mimmum

temperature for growth of tliis fungus ui culture is about 45 J^.,

he optimum 80°? and the maximum near 95°. In cucumbers and

melones a rapid decay develops at 55° to 85°. High humidity or

wet weather favors infections and development of decay.

39
Black rot may develop on any part of a watermelon. Many early

lesions do not show evidence of injury to the rind but inconspicuous

scratclies or sand pitting may furnish the chief mode of entrance of

the fungus.

Control Measures

Careful handling to avoid wounds and close inspection at loading

to eliminate all spotted melons should help in reducing decay in

transit. Since watennelons are not shipped by refrigeration, there

is little opportunity to check black rot at temperatures of 45° to

50° F.

(See 17, 65.)

BLOSSOM END ROT

Blossom end rot is usually not of much importance in the market

but in some seasons it causes serious blemishes, that open the way

for secondary infection by several kinds of organisms. It is generally considered a physiological disease caused by faulty nutrition

associated with irregular moisture supply and high temperature.

Pythium rot, black rot, and fusarium rot as well as others commonly follow blossom end rot so closely that it is difficult to determine the original cause of the trouble.

Blossom end rot on the market appears as dark green or brown,

definitely delimited areas, 1 to 3 inches in diameter, about the point

of the blossom attachment. The affected area is smooth, leathery,

and firm unless softened by the invasion of secondary molds or

bacteria.

Affected watermelons should not be shipped to market.

BRUISING (MECHANICAL INJURY)

Watermelons frequently show friction bruises, slight watersoaking, and discoloration of the rind due to mechanical injuries while

in transit. These injuries are most prominent on melons in contact with the floor or walls of the car. Wlien the straw or other

bedding is wet and dirty, friction against the floor causes serious

discoloration, sometimes called floor scald. Dark greenish-brown

spots also occur on the ends of melons where they come in contact

with each other or with the end of the car when the loads are

shifted. The blossom ends of watermelons are often depressed and

the adjacent flesh damaged. The latter two types of bruising occur

commonly in melons loaded lengthwise.

CHARCOAL ROT

Macrophomina phaseoli (Maub.) Ashby

Charcoal rot has been observed only rarely on the market on

watermelons grown in Missouri. Decay originates on the ground

side or at the stems of the melon. A light brown, fairly firm rot

is produced internally as well as externally. As a stem end rot it

resembles that caused by Diplodia, except it is lighter in color and

there is no surface mold or fruiting bodies evident. The skin of

the affected portion of the rind slips off readily under slight pressure. Very small black specks (sclerotia) may be visible in the

decaymg nnd or internal flesh. (See Muskmelon Charcoal Eot,

p. 30.) '

40
The causal fungus is in the soil. It causes most severe infection

in wet, warm seasons. Good soil drainage may offer some measure

of control. Melons infected with charcoal rot should not be shipped

(See 5J.) ^^

FUSARIUM ROT

Fusarium spp.

Fusarium rot of watermelons rarely causes as much damage as

it does in other types of melons (see Muskmelon, p. 32). However,

watermelons from Mexico occasionally suffer loss from this disease

(pi. 24, A). Infections usually occur at the stem or blossom end

although the ground sides of melons are sometimes invaded. Fine

white, cream-colored, or pink surface mold generally characterizes

this disease. The invaded rind and flesh is yellow to tan and moderately dry. With age these tissues become"spongy.

Infection takes place in injuries, or follows in lesions caused by

other diseases.

No effective method of control of this decay has been developed.

(See 95.)

INTERNAL RIND SPOT

An internal spot of the rind of watermelons has been observed

on the markets at various times since 1924 when it was ñrst noted

in melons from Georgia. Since that time it has been found in

watermelons from practically all melon-growing regions. Usually

the percentage of melons affected is ratlier low, but this is difficult

to determine since the melons must be cut to see the spots.

The brown, irregular, rustlike spots vary in size from mere specks

to almost 14 ii^ch in diameter (pi. 24, B). These spots of brown

tissue are fairly finn and coi-ky, and there is no soft decay associated with them. Sometimes the external surface of the rind shows

some mottling and occasionally small pimples are also present (see

Pimples, p. 42).

The exact cause of this trouble remains to be determined. At first

it seemed to be associated with drought in the field, but more recent

investigations suggest the possibility of virus infections being

responsible.

PHYTOPHTHORA ROT

Phytophthora spp.

Occurrence and Importance

Phytophthora rot of watermelons grown in Arizona, California,

and Mexico has caused serious loss in transit and on the market for

several years. The amount of decay varies greatly with the weather

at point of origin of the shipment. Some carlots have shown a loss

of over 300 melons on account of this disease. Watermelons grown

in the Southeast are seldom damaged by this disease.

Symptoms

The first signs of infection are small, irregular, somewhat watersoaked spots that later vary from grayish green to brown, depending on the variety of melon. On light-colored melons the lesion is

usually browner than on deep-green melons. At times there is

41
slight, brown zonation apparent. The affected rind is moderately

firm and does not become simken until the lesion is veiy large (pi.

21, A). Under humid conditions a white, somewhat cottony mold or

a feltlike sc-um covers the surface of the larger lesions (pi. 24, C).

At points of contact between melons in the load this mold is sometimes quite conspicuous (pi. 24, E). The larger lesions with greenish-brown color of the rind often penetrate 2 to 4 inches into the

fleshy pulp of the interior. The red flesh is somewhat watersoaked

and bleached but there is no other discoloration. In advanced stages

the white mold of the causal organism is evident over and around

the seeds (pL24,D).

Causal Factors

Several species of Phytophthora may cause rot of watermelons.

The most common are P. capsici (Leonian), P. faramtica (Dast.),

and P. cactonmi (Lib. & Cohn) Schroet. Each of these grow well

at 80° to 90° F. but little growth occurs below 50°.

Inoculation experiments with watermelons have shown that infection may develop without wounds as well as in injuries. At 70°

F. wound inoculations developed light brown l&sions 2 to_3 inches

in diameter in 5 days; at 54°, the lesions were 1/2 to 2 inches in

diameter. Contact inoculations without wounds produced lesions

% inch in diameter at 70° and about % inch in diameter at 54°

within 5 days.

Early held infections that pass unobserved at shipping time apparently account for much of the decay found on the market, although new infections by contact frequently cause decay in additional melons during transit and marketing. Wet seasons or heavily

irrigated soil provide most favorable conditions for phytophthora

infections in the field.

Control Measures

Watermelon shipments are not refrigerated, so low temperatures

cannot be used to control this decay. Careful inspection to eliminate infected melons at loading time should reduce the amount of

decay during transit and marketing.

(See 6, 39, U, 5!^, 80, 99.)

WATERMELON PIMPLES

Watermelons on the market often show more or less serious blemishes due to large numbers of pimples scattered over the rind. For

the most part these pimples are small, ranging from i/^g to i/g inch

in diameter. They are firm and in general suggest insect stings or

early stages of anthracnose. HowcA^er, no decay originates at these

pimples. Apparently watermelon fruit pimples may be caused by

more than one agent. In Mississippi small spots of powdery mildew

on the surface of watermelons give rise to pimj^les of various sizes.

Texas and Oklahoma watermelons have a type of pimpling shown

to be due to the tobacco ringspot Adrus.

{S&&37,67,69.)

PYTHIUM ROT

Pythium spp.

Pythium rot has been obser\^ed only in excessively moist situations

in the southern and midwestern watermelon-growing sections. The

42
disease is of minor importance on the market. Althonoh tlie symptoms vary somewhat with the different species of Pi/fhhnn involved

in general it may be said that they appear first as watersoaked spots

mat soon tnrn light brown, bluish brown, or cliorolate brown. The

decay progresses rapidly and the flesh becomes flaccid. In some

cases when the epidermis is nibbed off the decayed tissues have a

marshy odor. Under humid conditions some white surface mycelium

appears. At times this decay appears similar to phytophthora rot

(seep. 41).

(See 78.

RHIZOPUS ROT

See Muskmelons, p. 35 and pi. 22,5,

SCLEROTIUM ROT

Sc/erofium ro/fs/i Sacc. (Pe/Zicu/ana ro/fsi; (Curzi) West)

Sclerotium rot of melons grown in the United States is seldom

important on the market. However, Mexican watermelons on the

Chicago market in 1959 showed this decay affecting 30 percent of

the melons in several carlots.

This disease sometimes causes serious fruit rot in Florida and

Texas. In practically all fruit infections, the fungus enters on the

under side, usually through wounds. Sometimes" infections occur

on the sides and ends of melons where no injuries are apparent. A

small, watery, light-yellow discoloration of the rind is the first

evidence of disease. Discoloration and decay progress rapidly; in

several cases the rind cracks open and tlie fine, silky white mycelium

grows out in flat, fanlike radiations over the surface of the melon.

Small white, spherical sclerotia soon form in this mycelium and

within a few days thej^ appear as brown bodies resembling mustard

seeds.

Xo satisfactory control is known.

SOIL ROT

Rh'izoctonla solani Kuehn IPellicularia filamentosa (Pat.) Rogers)

Soil rot of watermelons is seldom of much importance on the

market. In wet seasons it is found occasionally on the ground side

of the melon. The first signs of this disease are small yellow or tan

spots. These later become brown as they enlarge. The affected

areas are fairly firm and sharply separated from the healthy tissue.

The cream-colored mold (Rhizoctonia stage) of this fungus is seldom seen on the lesions. The larger lesions may penetrate through

the rind but the red flesh is rarely decayed.

(See 56.)

SPECKLE

Watermelons grown in Florida and Texas sometimes show numerous small, pale-yellow to orange-yellow spots in the rind that detract from the appearance of the melons. These spots are superficial and usually vary in size from i/ie to 1/4 inch m diameter. The

discolored rind is smooth and firm. No decay is produced in tliese

spots and no organism seems to be associated with the discolored

area. The cause of the trouble is not known.

(See 56.)

43
STEM END ROT

Dip/od/a natalensis Pole-Evans

Occurrence and Importance

Stem end rot at times has caused greater loss in transit than anyother decay that affects watermelons. Although it also occurs on

melon fruits in the field, it is of minor importance there. The

pathogen does not attack fruit except through wounds or through

lesions produced by other organisms.

Symptoms

The first symptoms of the disease are a browning and shriveling

of the stem, so that it feels hollow Avhen pressed. Decay sets in at

the point of attachment of the stem to the fruit and consists of

softening and watersoaking of the tissues (pi. 22, A). As it progresses into the melon the afi'ected tissues become brown and shriveled. In advanced decay the shriveling becomes pronounced and

there is an abundant development of black pycnidia and dark-gray

mycelium (pi. 23). The infections usually occur at the stem end,

but they may also occur at wounds, and in the field, at the blossom

end of the melon.

Causal Factors

The causal agent, Diplodia natalensü. is a fungus identical with

or a close relative of a species of Dvplodia that attacks many other

plants, including cucumber, squash, and muskmelon fruits. It is

abundant on ripe or decaying vegetation in or near watermelon

fields. From these sources the spores of the fungus reach the cut

ends of the stems of cull melons or the blossom ends of imperfect

melons. In a short time it produces spores which serve to infect

sound melons through the wound made in cutting the stem, through

other wounds or bruises, through anthracnose lesions, rabbit injury,

and punctures made by the pickle worm. Infection can also take

place in transit from spores lodged in the bedding or produced on

infected melons. The cut stem is the ideal place of entry for the

causal organisms, because the sap which exudes serves to catch the

wind-borne spores and provides a good food supply for the fungus.

The decay progresses rapidly. At temperatures between 75° and

90° F., the fungus will grow through a stem % inch long and decay

the fruit to a line about 11/2 inches distant from the base of the

stem in 90 hours. It is not surprising, therefore, that melons appearing sound at the time of loading may show severe rot after

being in transit 4 to 5 days.

Control Measures

In harvesting, all decayed melons should be avoided. If a diseased

one is cut into, the knife should be sterilized in a 2-percent formaldehyde solution. The melons should be cut with the longest possible

stems.

^Vhen the melons are placed in the car or truck, the stems should

be reçut, and disinfecting paste should be applied to the cut surface.

The disinfectant should contain 6 percent of bluestone as a fungicide.

(See 56, 90.)

44
LITERATURE CITED

(1) ARK, P. A.

(2) ~^^^' ^^"^,^^^^^^ SPOT OF SQUASH. Plant Dis. Rptr. 38: 201-'

1938. A

and ToMPKiNs, C. M. 203.

28735^355''^'' ^'°"'" ""^ PUMPKIN FRUITS. Phytopathology

(3) BAEGER, W. R WIANT, J. S., PENTZER, W. T., and others.

1948. A COMPARISON OF FUNGICIDAL TREATMENTS FOR THE CONTROL OF

DECAY IN CALIFORNIA CANTALOUPES. Phytopathology 38: 1019-

(4) BARNES, W. C, and EPPES, W. M.

1955. PROGRESS IN BREEDING CUCUMBERS RESISTANT TO ANTHRACNOSE

(^\ BF.^TV T r'^Z'^ri *^^°=^^- ^mer. Soc. Hort. Sei. Proc. 65: 409^15. (&) BEATTBE, J. H., and DOOLITTLE, S. P

1951. WATERMEMNs. U.S. Dept. Agr. Farmers' Bui. 1394, 30 pp., illus

(Revised.) '^^ '

(6) BEOWN, J. G., and EVANS, M. W.

1933. A ^HYTOPHT^HOEA ROT OF WATERMELON. AriZ. Agr. Bxpt. Sta. TcCh.

(7) BRYAN, MARY K.

,^. ^1930. BACTERIAL LEAF SPOT OF SQUASH. Jour. Agr. Res. 10: 385-391

(8) BuscH, L. v., and WALKER, J. C.

1958. STUDIES OF CUCUMBER ANTHRACNOSE. Phytopatholt gy 48: 302-

(9) CARSNEE, E.

1918. ANGULAR LEAF SPOT or CUCUMBER: DISSEMINATION, OVERWINTERING AND CONTROL. Jour. Agr. Res. 15: 201-220, illus

(10) CHANDLER, F. B.

1940. BORON DEFICIENCY SYMPTOMS IN SOME PLANTS OF THE CABBAGE

FAMILY. Maine Agr. Expt. Sta. Bui. 402, 32 pp., illus.

1941. MINERAL NUTRITION OF THE GENUS BRASSICA WITH PARTICULAR

REFERENCE TO BORON. Maine Agr. Expt. Sta. Bui. 404, 307^00.

(12) CHIU, W. F., and WALKER, J. C.

1949. MORPHOLOGY AND VARIABILITY OF THE CUCURBIT BLACKROT FUNGUS.

Jour. Agr. Res. 78: 81-102, illus.

(13) and WALKER, J. C.

1949. PHYSIOLOGY AND PATHOGENICITY OF THE CUCURBIT BLACKROT

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(14) CHUPP, C.

1935. MACROSPORIUM AND COLLETOTRICHUM ROTS OF TURNIP ROOTS.

Phytopathologj' 25: 269-274, illus.

(15) COOK, A. A., WALKER, J. C, and LARSON, R. H.

1952. STUDIES ON THE DISEASE CYCLE OF BLACK ROT OF CRUCIFERS. Phytopathology 42 : 162-167.

(16) Cox, R. S., CARROL, V. J., and BENEDICT, R. A.

1957. STUDIES ON THE ETIOLOGY AND CONTROL OF THE RADISH PIT DISEASE. (Abstract) Phytopathology 47: 7.

(17) CRALL J. M., and DECKER, P.

1956. WATERMELON FRUIT ROT CAUSED BY MYCOSPHAEEELLA CITEULLINA.

(Abstract) Phytopathology 46: 10.

C18) CEOSSAN, D. F.. HAASIN, F. A., and ELLIS, D. E.

1954. PHYTOPHTHORA BLIGHT OF SUMMER SQUASH. Plant DiS. Rptr.

38: 557-559.

(19) DAVIS, W. H.

1925. DROP OF CHINESE CABBAGE AND OUR COMMON CABBAGE CAUSED BY

(SCLEROTINIA SCLEROTIORUM (LIB.) MASSEE). Phytopathology

15: 248-259, illus.

(20) DEARBORN, C. H.

1942. BORON NUTRITION OF CAULIFLOWER IN RELATION TO BROWNING.

N. T. (Cornell) Agr. Expt. Sta. Bui. 778, 29 pp.

(21) , THOMPSON, H. C, and RALEIGH, G. H.

1937. CAULIFLOWER BROWNING RESULTING FROM A DEFICIENCY OF BORON.

Amer. Soe. Hort. Sei. Proe. 34: 483-487.

45
(22) DOOLITTLE, S. P.

1916 CUCUMBER SCAB CAUSED BY CLADOSPOEIUM CUCUMERINUM. MlCIl.

Acad. Sei. Ann. Rpt. 17: 87-116, illus.

(23)

1920. THE MOSAIC DISEASE OF CUCUKBITS. U.S. Dcpt. AgF. Bul. 879.

(24) DRECHSLER, O.

1925 THE COTTONY LEAK OF CUCUMBER CAUSED BY PYTHIUM APHANIDEEMATUM. Jour. Agr. Res. 30: 1035-1042, illus.

(25) EARS, J. L., and MORRIS, L. L.

1957. DETERIORATION OP CUCUMBERS AT CHILLING AND NONCHILLING

TEMPERATURES. Amer. Soc. Hort. Sei. Proc. 69: 388-399.

(26) EDDINS, A. H.

1952 DISEASES, DEFICIENCIES AND IN.IURIES OF CABBAGE AND OTHER

CRUCiFERS. Fla. Agr. Expt. Sta. Bul. 492, 63 pp., illus.

(27) ELLIOTT, CHARLOTTE

1951. MANUAL OF BACTERIAL PLANT PATHOGENS. Chronica BotaDlCa.

Waltliam, Mass. 186 pp.

(28) ELLIS, D. E. _^„

1951. NOTEWORTHY DISEASES OF CUCUKBITS IN NORTH CAROLINA IN 194«

AND 1950. Plant Dis. Rptr. 35: 91-93.

(29) FELTON, M. W., and WALKER, .T. C.

1946. ENVIRONMENTAL FACTORS AFFECTING DOWNY MILDEW OF CABBAGE.

.Jour. Agr. Res. 72: 09-81.

(30) FERGUSON, W.

1938. BORON DEFICIENCY IN CAULIFLOWER. Sci. Agr. 18: 388-o91.

(31) GARDNER, M. W.

1918. ANTHRACNOSE OF CUCURBITS. U.S. Dept. Agr. Bul. 727, 68 pp.,

illus.

(32)

1920. PERONOSPOBA IN TURNIP ROOTS. Phytopathology 10: 321-322.

(33) GuBA, E. F. „.„,,__

1950. SPOILAGE OF SQUASH IN STORAGE. Mass. Agr. Expt. bta. Bul. 457,

55 pp.

(34) HARTER, L. L., and WEIMER, J. L.

1922. DECAY OF VARIOUS VEGETABLES AND FRU^ITS BY DIFFERENT SPECIES

OF RHizopUS. Phytopathology 12 : 205-212.

(35) HiGGiNs, B. B.

1917 A COLLETOTRICHUM LEAF SPOT OF TURNIPS. Jour. Agr. Res. 10:

157-162, illus.

(36) HORN, N. L., and WILSON, W. F.

1955. EVIDENCE OF SEED TRANSMISSION OF THE CUCUMBER ANTHRACNOSE

PATHOGEN. (Abstract) Phytopathology 45: 348.

(37) IVANOFF, S. S.

1957. POWDERY MILDEW PIMPLES ON WATERMELON FRUITS. Phytopathology 47: 599-602.

(38) KADOW, K. J., and ANDERSON, H. W.

1940. A STITDY OF HORSERADISH DISEASES AND THEIR CONTROL. 111. Agr.

Expt. Sta. Bul. 469, 52 pp., illus.

(39) KATSURA, K., and TOKURA, R.

1954. STUDIES ON PHYTOPHTHORA DISEASE OF ECONOMIC PLANTS : VIL

A BROWN ROT OF WATERMELON CAUSED BY PHYTOPHTHORA CAPsici LEONiAN. Scl. Rep. Toc. Agrie. Sarkyo Univ. 6: 38^8.

(40) KALTFMAN, J., FRIEDMAN, B. A., and HRUSCHKA, H. W.

1948. PREPACKAGING OF LONG ISLAND BROCCOLI, BRUSSELS SPROUTS, AND

CAUIJFLOWER. Pre-Pack-Age 1: 10-13.

(41) KREUTZER, W. A., BODINE, E. W., and DUKRELL, L. W.

1940. CUCURBIT DISEASES AND ROT OF TOMATO FRUITS CAUSED BY PHYTOPHTHORA CAPSici. Phytopathology 30 : 972-976.

(42) and GLICK, D. P.

1942. CONTROL OF ANTHRACNOSE SPOT OF HONEY-DEW MELONS. ColO.

Agr. Expt. sta. Farmers' Bul. 4: 9-11.

(43) and GLICK, D. P.

1943. THE HOLE OF PACKING METHODS IN THE INCREASE OF ANTHRACNOSE

OF HONEYDEW MELON FRUITS. Phytopathology 33: 245-248.

(44) LARSON, R. H., MATTHEWS, R. E. F., and WALKER, J. C.

1950. RELATIONSHIPS BETWEEN CERTAIN VIRUSES ATFECTING THE GENUS

BRASSICA. Phytopathology 40 : 955-962.

46
(45) LAYTON, DUKE V.

1937. THE PARASITISM OP COLLETOTRICHIUM LAGENARIUM (PASS.) ELL.

AND HALST. lowa Agr. Expt, Sta. Res. Bui. 223, 37-G7.

(4G) LINK, GEO. K. K., and GAKDNEH, MAX W.

1910. MARKET PATHOLOGY AND MARKET DISEASES OF VEGETABLES. Phytopathology 9: 497-520.

(47) McCuLLocH, L.

1011. A SPOT DISEASE OF CAULIFLOWER. U.S. BuF. Plant Indus. Bui.

225, 15 pp., lUus.

(48) MCLEAN, D. M.

1958. A SEED BORNE BACTERIAL COTYLEDON SPOT OF SQUASH. PLANT DíS.

Rptr. 42: 425-426.

(49) MACLACHLAN, J. D., and STRONG, W. F.

1948. SPRAYING AND DUSTING TURNIPS TO PREVENT WATER CORE, A DISORDER CAUSED BY BORON DEFICIENCY. Sci. Agi'. 28; Gl-65.

(50) MIDDLETON, J. T., and WHITAKER, T. W.

194t). SOME DISEASES OF CANTALOUPS AND HONEYDEW MELONS OBSER\i;D

IN SOUTHERN CALIFORNIA. Plant. Dls. Rptr. 30: 373-375.

(51) MORRIS, L. L., and PLATENIUS, H.

1939. LOW TEMPERATURE IN.JURY TO CERTAIN ^^ÎGETABLES AFTER HARVEST.

Amer. Soc. Hort. Sci. Proc. 30: 609-C13, illus.

(52) NATTI, J. J.

1958. CABBAGE MOSAIC AND LEAF SPOTTING IN STORAGE. Farm Res. 24 : 13.

(53) NEWHALL, A. G., and WILKINSON, R. E.

1949. STORAGE ROTS OF SQUASH IN NEW YORK STATE. Plant Dis. Rptr.

33: 220.

(54) NORTON, D. C, and ROSBERG, D. W.

1054. WATERMELON FRUIT ROT CAUSED BY PHYTOPHTHORA PARASÍTICA IN

TEXAS. Plant Dis. Rptr. 38: 854.

(55) PALMER, RAI.PH G.

1941. EFFECTS OF POTASH ON THE TIP BURN OF CABBAGE. Phytopathology 31: IS.

(56) PARRIS, G. K.

19.52. DISEASES OF WATERMELONS. Fla. AgT. Espt. Sta. Bui. 491, 48 pp.,

illus.

(57) PENTZER, W. T., WIANT, JAMES S., and MACGILLIVKAY, JOHN H.

1940. MARKET QUALITY AND CONDITION OF CALIFORNIA CANTALOUPS AS

INFLUENCED BY MATURITY, HANDLING, AND PRECOOLING. U.S.

Dept. Agr. Tech. Bui. 730, 74 pp., illus.

(58) PoNTis, R. E.

1945. PHYTOPHTHORA CAPSICI EN FRUTOS DE ZAPALLITO DE TRONCO. RCV.

Argent. Agron. 12: 17-21.

(59) POUND, G. S. „, i,.

1948. HORSERADISH MOSAIC. Jour. Agr. Res. 77: 97-114.

(60) and WALKER, J. C.

1948. STRAINS OF CUCUMBER MOSAIC VIRUS PATHOGENIC ON CRUCIFERS.

Jour. Agr. Res. 77: 1-12.

(61) RAMSEY, G. B.

19'>5 SCLEROTINIA SPECIES CAUSING DECAY OF VEGETABLES UNDER TRANSIT

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^^^^ 1935. PERONOSPORA IN STORAGE CABBAGE. Phytopathology 25: 955-957,

illus.

(63) . , SMITH, M. A., and WEIGHT, W. R. ,

1954. PERONOSPORA IN RADISH ROOTS. Phytopathology 44: 384-o85.

(64) RANGEL, J^J-^^^^^^^^^^^ j>r,^^sES OF CRUCIFEROUS PLANTS. Phytopathology 35: 1002-1007.

(65) RANKIN, HAR\-EY W.

1954. EFFECTIVENESS OF SEED TREATMENT FOR CONTROLLING ANTHRAC^NOSE

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(66) RICH^ ^\^i,„„ONIA ROOT ROT ON STORED HORSERADISH IN CONNECTICUT.

Plant Dis. Rptr. 42: 554.

47
(67) ROSBERG, D. W.

1053. ASSOCIATION OF A STIîAIN OF THE TOBACCO BINGSPOT VIRUS WITH

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(68) SHEFFEK, R. P.

1950. ANTHIÎACNOSE LEAF SPOT OF CKUCIFEKS. N.C. Agr. Expt. Sta.

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(69) SHEPHEKD, ROBERT J., and STKUBLE, F. BEN.

1956. TOBACCO RING-SPOT VIRUS ON WATERMELONS. Phytopathology 46 :

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(70) SMITH, E. F., and BRYAN, M. K.

1915. ANGULAR LEAF SPOT OF CUCUMBERS. Jour. Agr. Res. 5: 465-475,

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(71) SMITH, M. A.

1946. BACTERIAL SPOT OF HONEYDEW MELON. Phytopathology 36: 943-

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(72) and RAMSEY, G. B.

1953. BACTERIAL SPOT OF BROCCOLL Phytopathology 43: 583-584.

(73) and RAMSEY, G. B.

1956. BACTERIAL ZONATE SPOT OF CABBAGE. Phytopathology 46: 210-213.

(74) THOMPSON, B. D., and HALSEY, L. H.

1954. BLAC;K SPOTTING OF HARVESTED RADISHES. Pre-Pack-Age 82 : 21-30.

(75) and HALSEY, L. H.

1955. CONDITIONS ASSOCIATED WITH BLACK SPOTTING OF HARVESTED

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19.55. THE OCCURRENCE OF TWO TYPES OF HYPOCOTYI, DISCOLORATION OF

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(77) TOMPKINS, C. M., and TUCKER, C. M.

1937. PHYTOPHTHORA ROT OF HONEY'DEW MELON. Jour. Agr. Res. 54 :

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(78) , ARK, P. A., TUCKER, C. M., and MIDDLETON, J. F.

1939. SOFT ROT OF PUMPKIN AND WATERMELON FRUITS CAUSED BY

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(79) and TUCKER, C. M.

1941. ROOT ROT OF PEPPER AND PUMPKIN CAUSED BY PHYTOPHTHORA

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(80) TUCKER, C. M.

1931. TAXONOMY OF THE GENUS PHYTOPHTHORA DE BARY. Missouri Agr

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(81) VAN GUNDY, S., and WALKER, J. C.

1957. SEED TRANSMISSION, OVERWINTERING, AND HOST RANGE OF THE

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(82) WALKER, J. C.

1950. ENVIRONMENT AND HOST BESISTANCE IN RELATION TO CT7CUMBEK

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(83)

1952. DISEASES OF VEGETABLE CROPS. McGraw-Hill, 529 pp.

(84) , LE BEAU, J. J., and POUND, G. S.

1945. VIRUSES ASSOCIATED WITH CABBAGE MOSAIC. JOUT. Agr ReS 70'

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(85) , MCLEAN, J. G., and JOLIVETTE, J. P.

1941. THE BORON DEFICIENCY DISEASE IN CABBAGE. JouT. Agr Rcs 62-

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(86) , PiERSON, C. F., and WILES, A. B.

1953. TWO NEW SCAB-RESISTANT CUCUMBER VAEIETIES. Phytopathologv

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(87) WARDLAW, C. W., LEONARD, E. R., and BAKER, R. B. D.

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MELONS. Trop. Agr. (Trinidad) 11: 196-200, illus.

(88) WEBEK, G. F.

1929. ANGULAR LEAF SPOT AND FRUIT ROT OF CUCUMBERS CAUSED BY

BACTERIUM LACHRYMANS E. F. S. & BRY. Fla. Agr. Expt Sta

Bui. 207, 32 pp., illus.

(89)

1932. SOME DISEASES OF CABBAGE AND OTHER CRUCIFEBS IN FLORIDA

Fla. Agr. Expt. Sta. Bui. 256, 62 pp., illus.

48
(90) and OWEN, JOHN H.

1951. WATERMELON DISEASES IN THE GAINESVILLE AREA OF FLOKIDA FOB

,„,, „ THE 1951 SEASON. Plant Dis. Rptr. 35 : 355.

(91) WEIMEB, J. L.

1925. ALTERNARíA LEAF SPOT AND BROWN ROT OF CAULIFLOWER Jour

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(92) .

1920. EINGSP0T OF CRUCIFERS CAUSED BY MYCOSPHAEUELLA BIIASSICICOLA

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1926. A LEAFSPOT OF CRUCIFEROUS PLANTS CAUSED BY ALTERNARÍA HERCÚLEA. Jour. Agr. Res. 33: C45-C50, illus.

(94) and HARTER, L. L.

1923. TEMPERATl'RE RELATIONS OF ELEVEN SPECIES OF EHIZOPUS. Jour.

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(95) WlANT, .J. S.

1937. INVESTIGATIONS OF THE MARKET DISEASES OF CANTALOUPES AND

HONEY DEW MELONS. U.S. Dept. Agr. Tech. Bui. 573, 47 pp.,

illus.

(96)

(97)

1938. MARKET STORAGE STUDIES OF HONEY DEW MELONS AND CANTALOUPES. U.S. Dept. Agr. Tech. Bui. 013, 10 pp., illus.

1939. SPECIES Oe PHYTOPHTHORA RESPONSIBLE FOR MARKET DECAY OF

WESTERN HONEY DEW MELONS AND CANTALOUPS. Plant DÍS.

Rptr. 23: 322.

(98)

1943. AN ANALYSIS OF MARKET INSPECTION REPORTS ON SPOILAGE OF

CANTALOLIPS AND RELATED MELONS. Plant DiS. Rptr. Suppl. 138,

145-lCl.

(99) and TUCKER, C. M.

1940. A ROT OF WINTER QUEEN WATERMELONS CAUSED BY PHYTOPHTHORA

CAPSici. Jour. Agr. Res. GO: 73-88, illus.

(100)

1945. MYCOSPHAERELLA BLACK EOT OF CUCURBITS. JoUr. Agr. ReS. 71:

193-213, illus.

(101) and BRATLEY, C. O.

1948. SPOILAGE OF FRESH FEIHTS AND VEGETABLES IN RAIL SHIPMENTS

UNLOADED AT NEW YORK CITY. 1935-1942. U.S. Dept. AgT.

Cir. 773, 02 pp.

(102) WILES, A. B., and WALKER, J. C.

1951. THE RELATION OF PSEUDOMONAS LACHRYMANS TO CUCUMBER FRUITS

AND SEEDS. Phj'topathology 41: 1059-1004.

(103) WOLF, F. A.

1917 A SQUASH DISEASE CAUSED BY' CHOANEPHORA CUCUKBITARUM.

Jour. Agr. Res. 8: 319-328, illus.

(104) WRIGHT, R. C, ROSE, D. H., and WHITEMAN, T. M.

1954 THE COMMERCIAL STORAGE OF FRUITS, VEGETABLES, AND FLORIST

NURSERY STOCKS. U.S. Dcpt. Agr. Handbook 60, 77 pp.

(105) YOUNG, PAUL A.

1936 SCLEROTINIA ROT OF SQUASH AND PUMPKIN. Phytopathology 26.

184-190.

49

PLATE 1.—Cabbage disease : A, Watery soft rot ; B, alternaría rot.
r

^4.

iJt,^-<*

^^ ^>^:<-^

PLATE 2.—Cabbage disease: A, Black rot of stem and black leaf speck on

leaves ; 1Î, black rot at stem and midrib.
PLATE 3.—Broccoli and cabbage diseases: A, Broccoli bacterial spot; B, broccoli gray mold rot ; C, cabbage bacterial soft rot ;. D, cabbage zonate spot ;

E, cabbage downy mildew; F, alternaría leaf spot.
PLATE 4.—Cauliflower and cabbage diseases: A, Cauliflower downy mildew;

B, cabbage downy mildew.
y¿I

r^â?*^' .<^^ "...

.^ ^ " w**-»,^

-••>.

*r

^. #

PLATE 5.—Cabbage and brussels sprout diseases: A and B, Cabbage thrips

injury ; C, brussels sprout rhizopus rot ; D, brussels sprout ring spot.
PLATE 6.—Cauliflower disease: A, Brown rot (Alternaría) ; B, bacterial soft rot.
PLATE 7.—Radish disease: A and B, Downy mildew; C, black spot.
PLATE 8.—Rutabaga and turnip diseases: A, Black rot; B, watery soft rot;

C, alternaria rot.
PLATE 9.—Chinese cabbage disease: Black leaf speck.
PLATE 10.—Cucumber injury and disease: A,

B and C, bacterial' Low temperature breakdown;

spot.
PLATE 11.—Cucumber, squash, and honeydew melon diseases: A and B, Cutuml)er black rot; C, cucumber anthracnose ; D. cucumber cottony leak: E, squash

fusarium rot; F, honeydew melon alternariit rot following' chillinK injury.
«»#*»Ji

«áí^-

PLATE 12.—Honeydew melon disease : Anthracnose.
PLATE 13.—Honeydew melon disease: A, Alternaria rot; B, bacterial spot.
PLATK 14.—Honevdew melon disease: Fusarium rot.
PLATE 15 —Honeydew melon disease: A, Phytophthora rot; B, pink mold rot.
PLATE 16.—Cantaloup and honeydew melon diseases: A, Cantaloup cladosporium rot ; B, honeydew rhizopus rot.
PLATE 17.—Squash diseases: A, Black rot; B, alternaría rot following lowtemperature injury (stored at 40° F. for 35 days).
PLATE 18.—Sqiiasli disease: A, Blaek rot; B, alternaria rot; C, phytophthora

rot.
PLATE 19.—Squash disease : Rhizopus rot.
PLATE 20.—Watermelon disease; A, Anthracnose; B, black rot.
-^•^

PLATE 21.—Watermelon disease : A, Phytophthora rot ; B, anthracnose.
PLATE 22.—Watermelon disease: A, Stem end rot; B, rh izopus rot.
PLATE 23.—Watermelon disease: Stem end rot.
PLATE 24.—Watermelon disease: A, Fusaiiura rot; B,

C, D, and E, phytophthora rot.

internal rina spot;