niAjfVy,«.v>i 4%L.U e V^v, * /t ^ 2-

lARY

BEAN DISEASäS-«^^»'*^

How To Control Them

Agriculture Handbook No. 225

Asricultural Research Service

UNITED STATES DEPARTMENT OF AGRICULTURE
CONTENTS

Control practices 3

Using resistant varieties 3

Using disease-free seed 3

Crop rotation 3

Field sanitation 4

Seed treatment 4

Diseases of snap beans and dry

beans 4

Bacterial blights 4

Mosaics 8

Curly top 12

Anthracnose 13

Rust 15

Watery soft rot 18

Powdery mildew 21

Root rots 22

Page

Diseases of snap beans and dry

beans—-Continued

Root knot 24

Ashy stem blight 26

Angular leaf spot 26

Web blight 27

Baldhead 28

Sunscald 30

Diseases of lima beans 31

Downy mildew 31

Pod blight 32

Bacterial blight 34

Seed pitting 35

Stem anthracnose 37

Diseases of beans in transit and

storage 38

This handbook presents some information formerly contained

Farmers' Bulletin No. 1692, Bean Diseases and Their Control.

CroWliIhr(u¡nA¡iiculliiral?toa'

Washington, D,C. Issued June 1962

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

Washington 25, D.C.—Price 25 cents
BEAN DISEASES—HOW TO CONTROL

THEM

By W. J. Zoumeyer and H. Rex Thomas, Crops Research Division, Agric^llural Research

Service

Diseases of beans are causing severe and widespread damage to

this valuable crop every year in the United States. In some seasons

they may cost farmers from $15,000,000 to $20,000,000. Anyone who

grows beans—whether they are to be marlfeted as a green vegetable,

dried, canned, frozen, or used as seed—should give serious effort to

preventing losses from disease.

Some of the common diseases of beans result in death of the young

seedlings; some result in injury or death of the growing plants; and

some result in spots on pods and seeds that make the product unsalable. Most of the serious bean diseases are caused by parasites—chiefly

fungi and bacteria, which cannot be seen Avithout a microscope, and

viruses, which cannot be seen even with a compound microscope.

Some are caused by such things as extreme heat. Some show that

the soil in which beans are being grown contains either too little or

too much of one or more minerals.

Fungi and bacteria enter bean plants through natural openings or

wounds or even where there are no such openings. They then multiply within the plant tissues and cause spotting of leaves and pods,

wilting of tops, or rotting of roots or other plant parts. Frequently

they kill the i^lants. In cool, wet soils, fungi commonly cause decay

of planted bean seed.

A fungus produces a mass of threadlike growths, called mycelia.

The mycelium produces specialized branches or fruiting bodies that

yield spores. When the spores have matured they can germinate

wherever moisture is present. Fungus spores are scattered by wind,

rain, insects, and farm animals. They can be carried from field to

field in soil clinging to farm implements or to the farmer's shoes.

Disease-producing bacteria are one-celled organisms that increase

by dividing. Once they have entered a bean plant, they increase

rapidly within it and may infect all its parts. A fluid called bacterial

ooze flows out onto leaf, stem, and pod surfaces of the infected plant

and gradually dries. This fluid contains millions of bacteria.^ Bacteria can be carried from plant to plant by rain, by insects, by irrigation and drainage water, or on the hands and clothing of field workers.

Some kinds of disease fungi and bacteria are carried from one bean

generation to the next in the seed.
Plant virases, altliougli not so weH understood as fungi or bacteria,

are known to be spi'ead fi-oni one bean plant to another very easily.

They are carried chiefly by aphids, or plant lice, and other insects.

Some are carried in the seed.

Diflferent kinds of fungi and bacteria affecting beans have different

needs as to teni])erature, rainfall, soil moisture, and other features of

environment. For example, the bean disease known as curly top, the

\ ¡rus of which is spread only by the beet leafhojiper (frequently called

white fly in some parts of the West), is serious only where climate

favors tills insect. Since beans are grown in all regions of the united

States, under many kinds of environmental conditions, the importance

of any one bean disease varies widely among different localities.

Ijosses fi-om any one disease vary from year to year, also according

to seasonal weather conditions. For example, in seasons of heavy

I'ainfall and high humidity, greater losses result from the bacterial

blights, anthracnose, and rust than in dry years; and in seasons when

cool weather and high soil moisture prevail, heavy losses must be

expected from root rot.

This handl)ook tells how to guard against infection of bean crops,

how to identify each of the principal bean diseases, and what control

practices are currently used. Kecommended bean varieties that have

proved to be immune to certain diseases are discussed.

Soil fumigants and other chemicals recommended here

as means of controlling bean diseases are poisonous to

man and animals when taken internally. Some of them

cause a rash if they even come into contact with the

human skin. When using these chemicals be very careful to keep them away from the mouth, eyes, and nostrils.

If a large quantity of seed is to be treated with a chemical in dust form, put on a respirator or dust mask to

avoid inhaling any of the chemical. If a large quantity

of chemical in solution is to be applied, put on oiled

leather gloves and a rubber or oilcloth apron. In pouring out the unused solution, take care to see that it does

not stand in puddles but soaks into the ground. After

chemicals have been used, the vessels that have contained them should be thoroughly cleaned, and the hands

and clothing of the user should be washed. Never store

poisonous chemicals within the reach of children.
CONTROL PRACTICES

Using Resistant Varieties

The most satisfactory way of controlling certain bean diseases is to

gro\Y varieties that are resistant to them. A grower should never

plant a bean variety known to be susceptible to a disease when he can

jDlant a suitable variety known to be resistant. In the discussions of

individual diseases that follow such desirable resistant varieties of

beans are listed, together -with methods of control.

Using Disease-Free Seed

Because some of the principal diseases of beans are carried by the

seed, growers should make every effort to use seed from disease-free

crops. Some of the seedborne diseases cannot develop in localities

that have low rainfall and high temperatures during the growing

season; therefore seed produced in the Mountain and Pacific States

is less likely to carry disease than seed grown east of the Rockies, and

is preferable for planting in any region.

A grower who saves bean seed from his own crop in order to avoid

the expense of buying seed usually is making a mistake. This practice

makes planting only a little less expensive, and may lead to heavy loss

in the value of the crop. Seed should be bought from reputable firms,

and should not be selected on the basis of price alone. Producing

high-quality, disease-free seed is a costly process. It requires special

knowledge of the characteristics of different varieties and special

practices for keeping the stock pure and true to type and maintaining

or improving quality. Seed companies employ experts for this work.

They are better equipped than pri\-ate bean growers to produce highgrade, noninfected seed, and the growers should be willing to pay a

higher-than-average price for such seed.

Crop Rotation

The germs of most bean diseases can live in the soil for several

years, on dead plant material, ready to infect a new bean crop. If

beans are grown year after year where such germs are present in the

soil, the germs multiply. How long a crop rotation should be used to

control some bean diseases or hoAv much time is needed to starve out

some of the disease organisms in difl'erent climates and difl'erent soil

types is not known. It seems possible that in the Mountam States

the bacteria causing common and halo blights and bacterial wilt can

overwinter in the soil for 2 years ; so a 3-year rotation is recommended

for western beanfields where these diseases have appeared. The bean

rust fungus, so far as is known, lives only 1 year; the watery soft rot

fungus sometimes lives as long as 10 years. In some of the following

discussions of individual diseases, recommendations are made as to

what crops should be rotated with beans where these diseases are

present and how long the rotation should be.

3
Field Sanitation

The lives of some disease germs in the soil are shortened if dead

plant material decays rapidly. For this reason, refuse remaining in

a field after threshing and straw returned to a field should be plowed

under as soon after harvest as possible.

Some of the fungi, bacteria, and viruses causing bean diseases attack

weeds growing in beanfields or nearby. The fungus causing watery

soft rot, for example, is very likely to attack rag-weed. When a

bean crop has been seriously affected by disease and the field is abandoned, any weeds in or near the field should be plowed under as soon

as possible, to prevent infection of future crops. Certain viruses affecting beans are carried to beans from other crops by insects. For

example, the virus causing yellow bean mosaic can be carried to beans

from sweetclover, red clover, and gladiolus. Beans should not be

planted near any crop known to harbor a virus affecting beans, and any

known plant carrier of such a virus growing wild along ditchbanks

or fence rows near a beanfield should be eradicated.

Seed Treatment

Disinfecting bean seed with chemicals has failed as a method of

controlling seedborne diseases. It destroys the germs on the surface

but cannot reach those beneath the seed coat without injuring the

seed itself. Dusting the seed with certain chemicals has proved

beneficial in preventing seed decay and increasing the vigor of the

plants produced. Where beans are to be planted in cool, wet soils,

good results in preventing seed decay are usually obtained by dusting

the seed with Spergon at the rate of 11/2 ounces per bushel or with

Delsan at a rate of 1% to 2 ounces per bushel.'

DISEASES OF SNAP BEANS AND DRY BEANS '

Bacterial Blights

Bacterial blights are among the principal diseases of beans wlierever

rain falls frequently during the growing season. In certain parts

of the United States, some blight damage to bean crops occurs every

year. Only in some parts of the Mountain and Pacific States are

bean crops fairly safe from losses caused by this group of diseases.

Bean diseases known in the United States as bacterial blight include

common blight, halo blight, bacterial wilt, and fuscous blight. Each

of these is caused by a different kind of bacteria, but each produces

very similar symptoms on bean plants.

Description

Bacterial blights show up strikingly on bean leaves. First, small

water-soaked spots appear on the underside of the leaf. (These spots,

^ Mention of specific products does not imply recommendation by the U.S.

Department of Agriculture over others of a similar nature not mentioned.

^ In this section, except where lima beans are mentioned, the word ''beans"

signifies snap and dry varieties only. Some of the diseases discussed here are,

however, serious as diseases of lima beans.
FIGURE 1.—Bacterial blight on leaves of snap beans. A, Halo bliglit as It develoiis iintler cool conditions. Baoli lesion is a siKit of dead tissue surnnnided

by a gi-eenish-yellow area. B, Common bacterial blight. The lesions have

turned i)rown and have merged to form several extensive dead areas.

and dead areas witliin living tissues in general, are called lesions.)

As the spots develop, dried bacterial ooze usually can be seen in the

center of each. In halo blight, under cool conditions, a greenishyellow circle forms around each spot (fig. 1, A). Blight lesions

may turn brown, and different spots may merge, forming an extensive

brown, dead area (fig. 1, B). In time every leaf on the plant may die

and fall.

On stems of young bean seedlings, also, blight lesions sometimes

appear as small water-soaked spots. Such a spot gradually grows

larger and then turns a reddish color. On older plants, long reddish

lesions may appear extending lengthwise along the stem. When pods

are beginning to form on blight-infected bean plants, a khid of

lesion known as stem girdle or joint rot often appears. This starts

as a small water-soaked area usually at one of the lower nodes of the

plant. Growing larger, the lesion encircles the stem, usually when the

pods are half mature. Later it turns an amber color. Ofteti the increasing weight of the top causes the stem to break at the diseased

node.

Bacterial blight damage to bean pods is often severe (fig. 2). Very

small water-soaked spots appear and grow larger. Usually each spot

contains a series of irregular bands of different colors, one surrounding

another, and the tissue around each spot is reddish brown or brick red.

Finally the spots become dry and sunken, often with a covermg of

dried bacterial ooze.

The bacteria may infect the hinge, or upper suture, of the pod,

causing discoloration of this part and water soaking of tissue on both

sides of it. Through the hinge they may attack the seed. If pods

625259°—62-
-Pods severely spotted by bacterial blight. Bacterial ooze has hardened at the centers of lesions.

become infected wliile still young, the bacteria may discolor the hilum

(the part of a seed at which it is attached to the pod) and surrounding

tissue, giving the tissue a varnished appearance. On light-colored

bean seed these effects are conspicuous, but on dark-colored seed they

are likely to be overlooked. Infected seed may appear to be entirely

healthy. Infection of young pods may have much more destructive

results, causing the seed to rot completely or be reduced to empty,

shriveled seedcoats (fig. 3).

FiGUBE 3.—These bean seeds have been shriveled and in some instances killed

by common bacterial blight.
When seed badly affected by bacterial blight is planted, the seedlings produced are likely to be stunted and may not push through

the ground at all. Some of the seedlings may grow to fairly o-ood

size; but usually, if such a seedling is examined closely, a lesion^will

be found at the node where the cotyledons (seed leaves) were attached.

Halo blight, if it occurs mider cool conditions, can be identified

by the halolike greenish-yellow areas, roughly circular, that surround

the leaf iesions (fig. 1, .4). In early stages of development, leaves

of bean plants infected with halo blight have a characteristic yellow

color. Young leaves of plants infected with common blight turn

brown rapidly and look as if they had been burned (fig. 1, B).

The ooze of common blight is yellow; that of halo blight is light

cream or silver.

Bacterial wilt does not commonly produce the conspicuous watersoaked areas on stem, leaf, and pod that are characteristic of common

blight and halo blight. Pod infection witli bacterial ivilt often cannot

be detected until the pod is opened. The infected seeds are yellow ancl

usually shrunken.

Fuscous blight resembles conniion blight so closely that positive

identification can hardly be made without laboratory tests.

Cause

The organisms causing bacterial blights of snap and dry beans

are as follows: Common blight, Xanthoinonas pliaseoli (E. F. Sm.)

Dows. ; halo blight, P^eudomonnH phaaeolieoTa (Burkh.) Dows. ;

bacterial wilt, f'orynehncteriwni faccumfrifienx (Hedges) Dows.;

fuscous blight, X. phaxeoli var. fuxfinns (Burkli.) Starr & Burkh.

Blight bacteria connnonly enter bean plants through the stomata

(breathing pores) of leaves, stems, and pods. Rain and damp Aveather

favor spread and development of blight bacteria, especially those of

common, fuscous, and halo Iiliglits. I)ampness causes greater quantities of ooze to form and greater quantities of bacteria to adhere to

insects and other carriers. Also, the splashing of rain spreads the

bacteria from plant to plant. Heavy dews, driving rains, and

hailstorms are particularly favorable. When a beanfield is wet, these

bacteria can spread rapidly from a few infected plants to other

plants throughout the field. Warm temperatures favor common

blight, fuscous blight, and bacterial wilt; cool temperatures favor

halo blight.

In addition to being carried by bean seed, blight bacteria can live

over winter on dead plant material in the soil, possibly for 2 years.

Control

To prevent losses from bacterial blight, the bean grower should

carefully avoid using infected seed. He should use only seed grown

in the far West = where, for reasons of climate, blight epidemics dc

not occur. A place where blight epidemics occur infrequently is not

a good source of bean seed because there is no way of predictmg in

what years it will be free of epidemics.

' In this handboolî, "the far We.st" refers to the regions lying west of the

Great Plains.
Since blifïht Ijacteria can live over winter in tlie soil possibly for 2

years, planting of beans must be discontinued for 2 years on land

"where a crop has been infected with blight, and it is unwise to plant

beans on the same land for more than 1 year at a time even if infection

has not been discovered there. Lima beans, soybeans, and cowpeas

should not be rotated with snap beans and dry beans, because each of

these plants is susceptible to one or more kinds of blight.

No commercially grown varieties of snap or dry beans have proved

to be highly resistant to common blight. Dry bean types such as

Pinto, Great Northern, Red Mexican, and pea beans and some varieties

of the semipole and pole types of snap beans are fairly tolerant of halo

blight; that is, they may be infected with it and yet develop almost

normally. Little is known about resistance of snap and dry beans to

bacterial wilt.

To avoid spreading blight from infected to noninfected bean plants,

the bean grower should avoid working in his fields when the plants

are wet.

Mosaics

The bean mosaics are a gi'oup of diseases bean growers are likely

to overlook even in years when these diseases are serious. The vims

causing a mosaic disease may infect every plant in a field and reduce

yield, quality, and selling price of the product considerably, but it

rarely kills a plant and often produces no conspicuous symptoms.

In many parts of the United States mosaic diseases spread widely

through beanfields in some years, causing severe losses.

Descripfion

The principal mosaic diseases of beans are (1) common bean mosaic,

(2) a variant strain of this disease, and (3) yellow bean mosaic. The

first two affect only beans and a few related plants. Under field conditions it is practically impossible to tell these two apart. Yellow

mosaic affects many plants in addition to beans.

Common bean mosaic, the most widespread of the three, results

in stunting of the plant and mottling and malformation of leaves

(fig. 4). Affected leaves usually have irregular-shaped light-yellow

and liglit-green areas of various sizes. This mottling is sometimes

the only evidence of the disease. In addition there may be considerable puckering and other alterations in leaf shape. The affected leaves

may be narrower and longer than normal leaves, with considerable

downward cupping due to unevenness of growth of the leaf tissues.

Bean plants infected with the common mosaic virus early in the season

are likely to turn a yelloAvish green, often are dwarfed and spindling,

and usually do not produce more than a small crop. Plants attacked

late in the season may produce an almost normal crop.

On beans of certain varieties the variant strain produces symptoms

that cannot be distinguished from those of common mosaic. Yellow

bean mosaic has distinctly different symptoms. In this disease the

8
FlGUUE 4.—The iiKittliiig, puckering, and uialfoniiatloii of these beau leaves were

caused hy cniu]uou beazi iimsaic, a virus disease.

contrast between the yellow and the green areas of the aft'ected leaves

is nmcli more intense (ñg. 5), and the plants become decidedly

dwarfed and bunchy.

Both common and yellow bean mosaic sometimes seriously deform

pods (fig. 6) and cause their surfaces to become i-ougli and shiny.

Cause

The bean mosaics are caused by viruses, which are carried most

commonly by aphids, or plant lice. The aphids spread the viruses

by feeding on infected and then on healthy plants. Yellow bean

mosaic is spi-ead to beans fi-om sweetclover, crimson clover, or red

clover, and gladiolus—and, of course, from other beans. The virus

of any of the principal mosaic diseases of beans cannot be spread
FIGURE ñ.—Yellow mosaic- is identiflecl by the striking conti-ast between j-ellnw

anil green areas of tlie alïectefl leaves.

from infected to liealthy beans by cultivation, roguing, or picking,

altliougli the viruses of several less common bean mosaic diseases can

be spread by these operations. The viruses of common bean mosaic

and its variant usually spread through all parts of a plant, even

entering some seed. Seed thus infected may look normal, but they

carry the virus and produce diseased plants. Some plants produced

from such seed fail to mature. Others, slightly infected, mature but

FifiUEE 6.—Pods severely deformed by yellow bean mosaic.

10
produce diseased seed. The virus of yellow bean mosaic usually

spreads through all plant parts other tlian the seed, but it never enters

the seed.

Symptoms of mosaic disease usually develop about 10 days after

infection. Under cool conditions, however, the infected plants never

show any noticeable symptoms.

Confro/

The one satisfactory method of control for common bean mosaic

and its variant is to use snitaljle mosaic-resistant bean varieties.

This method does not apply to yellow bean mosaic, for no bean A-ariety

resistant to many strains of the virus producing this disease lias yet

been developed. "Where yellow bean mosaic is pi'e\alent, fence rows

and ditchbanks should be kept free of sweetclover, crimson clover,

and red clover. It is advisable not to plant beans close to fields of

these clovers or of gladiolus.

Here is a list of the most popular commercially grown mosaicresistant varieties and strains of snap and dry beans and some of the

susceptible varieties and strains : *

SNAP I5EANS

Rrííiníant to Common Bran Mosaic

and Its Variant

Bush Types—

Rush Blue Lake, Conteuder, Cornell

14, Earligreen, liarliwax. Extender,

Oallatin .^0, Harvester, Imprnved

Higrade, Pearlgreen, Processor,

PureKold Wax, Resistant Asgrow

Valentine, Resistant Tendergrcen,

Slenderwhite, Slimgreen, Tendercrop, Teudergreen 32304, Tenderlong 1.1, Tenderwhite, Topcrop,

Wade, Wadex, and White Seeded

Tenderorop

Pole Tvpes—

Blue Lake Stringless Nos. S2, 228,

231, and F.ll. 1, Kentucky Wonder,

Kentucky 191, McCaslan, Potomac,

and Rialto

Snseeptittle to Common Bran Mosaicand Its Variant

Bush Types—

Hountifnl, Brittle Wax, Cherokee,

Kinghorn Wax, Lanrtreth Stringless

Green Pod, Plentiful, Slendergreen, Tendergreen, and Top Notch

Golden Wax

DRY BEANS

Resistatit to Common Bean Mosaic

Miehelite 62, Great Northern U.I. Nos.

31. .'>9. and 123, Great Northern No.

1140, Pinto U.I. Nos. 72, 78. and 111,

Columbia Pinto, Red Mexican U.I.

Nos. 3, 34, and 35, Robu.st, Saginaw,

Sanilae, Seaway, and Small White

F.M. 51

Resistant to Variant Strain

Columbia Pinto, Gratiot, Great Northern U.I. Nos. 31, 59, and 123, Great

Northern 1140, Red Mexican U.I.

No. 35, and Seaway

Siiscciitihlc to Common Bean Mosaic

Pinto : New Mexico Nos. 295 and 641,

San Juan strain, Red Kidney (light

and dark strains), Small White (regular strain), Pink, and Cranberry

Siisceptihle to Variant Strain

Miehelite, Pinto U.I. Nos. 72, 78,

and 111, Red Mexican U.I. Nos. 3

and 34, and Sanilae

'The initials "U.I." before a name signify that the variety or strain was

produced by the University of Idaho.

11
Curly Top

Curly top, a vims disease of many cultivated and wild plants, sometimes gives serious trouble in beanfields of Utah, Idaho, Washington,

Oregon, California, and other western States. In most of these States

the disease is not serious on Ijeans every year but almost completely

ruins the crop when there is a large population of the beet leafhopper—the only known insect that carries it.

Description

Plants infected in the seedling stage turn yellow and usually die.

On plants infected at later stages the leaves pucker and curl downward (fig. 7) and the veins clear. Young leaves on infected plants

FlGUKE 7.—Three bean plants of eiiual ajie. Tlie oue in tlie center was stunted

and deformed by euiiy top.

of some varieties are decidedly dwarfed and have a darker-thannormal green color. Cupping of the leaves sometimes continues until

each leaf looks like a small green ball. Often the young leaves cease

to develop, then turn yellow and curl downward. Leaves thus affected

are thicker than normal and are very brittle, readily breaking oif

from tire main stem. Generally, under these conditions, the plants

die before pods develop. Any pods that do develop are decidedly

dwarfed.

12
Plants infected late in the season do not always develop typical

symptoms of the disease, and o-enerally grow to maturity. Often,

however, the pods they produce are stunted.

Cause

Curly top is caused by a virus, which is spread from plant to plant

only by the beet leafhopper. This insect, frequently referred to in

some parts of the West as the white fly, is known scientifically as

Gircultfer tenellun (Baker). It overwinters and produces its spring

young on various perennial and winter annual weeds and other plants

in abandoned and sagebrush areas of the far West. Many of these

plants are susceptible to the curly top virus, and the spring brood

of leafhoppers may carry the \'irus from them into cultivated ñelds

of beets, beans, tomatoes, and other crops. Leafhoppers feeding on

plants in abandoned and desert areas usually migrate wlien tliese

plants begin to mature and dry. Symptoms appear on infected bean

plants about 10 days to 2 weelis after infection, and a severely infected

plant may die within a few weelis after that. The curly top virus

is not seedborne.

The severity of curly top epidemics varies from year to year according to the size of the beet leafhopper population and the percentage

of tlie insects carrying the virus.

Confro/

The best way to control curly top of beans is to grow suitable resistant varieties. Dry bean varieties resistant to both curly top and

common mosaic are Eed Mexican U.I. Nos. 3, 34, and 35, Great

Northern U.I. No. 31, Columbia Pinto, and Pinto U.I. Nos. 72, 78,

and 111. Dry beans resistant only to curly top are Pink and Red

Mexican. Idaho Bountiful and Golden Gem are bush snap beans

which are resistant to both curly top and common bean mosaic viruses.

Among susceptible varieties of snap beans, some that can be grown

without danger of severe loss from curly top in years of medium

leafhopper population are Idaho Piefugee, Landreth Stringless

Green Pod, and Puregold Wax. Among the varieties most seriously

damaged by curly top are Plentiful, Bountiful, and Kentucky Wonder.

Since the curly top virus is not seedborne, bean seed grown where it

is prevalent can safely be planted in any part of the country.

Anthracnose

Bean anthracnose, a disease caused by a seedborne fungus, occasionally causes losses of snap and dry beans in the Eastern, Midwestern,

and Southern States. The anthracnose fungus is favored it the

weather during the growing season is moderately cool and is lunnicl

or rainy. Infection may occur on any part of the plant above

the ground and at almost any stage of growth. Since the use ot

western-grown bean seed has become widespread, bean anthracnose

has been less prevalent.

13
Description

Bean seed infected with the anthracnose fmigns have dark, sunken

lesions of various sizes, which may extend througli the seed coat into

the cotyledons. When mature, tlie lesions Iiave pinkish masses of

spores at their centei'S. Lesions on the stems are oval sunken cankers,

extending up and down the stem. Their principal color ranges from

brown to very dark brown, and they have purplish to brick-red borders. The fungus may so weaken bean stems that they are easily

broken in cultivation or by a strong wind.

Anthracnose infection of bean leaves generally follows the veins

on the undersides causing them to become purplisli or reddish. It

may have this effect on most of the veins of a leaf or on only a few

of them. A severe attack causes angular dead spots to appear on the

upper leaf surfaces, giving the leaves a ragged appearance.

It is on the pods, however, that the symptoms of the disease are

most conspicuous. Here the lesions begin as very small reddishbrown elongated spots, often numerous. These spots gradually become more or less circular and are sunken at the center. A border

of a rusty to brown color forms around each of them. Mature lesions

(fig. 8) may be one-fourth inch or larger in diameter. During moist

41,4Êik âà. ^^

FiGUEE S.—Potls in an advanceil sta;:e of anthracnose infection, with niayses

of light-colored spores at tlie centers of lesions.

weather the fungus produces numerous spores, which give the cankers a pinkish color. When the pods are being picked, yomig lesions

are sometimes hard to detect; but under favorable conditions they

may develop into conspicuous cankers within a few days.

Cause

Anthracnose is caused by the fungus ColJetotrichum liiidemuthiamwi (Sacc. & Magn.) Briosi & Cav., which attacks not only beans

but some other related plants. Spores produced in lesions on bean

pods, stems, and young leaves are scattered by wind and rain to other

plant parts and to other plants. They may be carried, also, on the

bodies of insects, on the hands of bean pickers, on farming implements,

and in various other ways. In some localities there is evidence that

wild animals feeding on or running among diseased plants spread

(lie infection. A sticky substance surromids the spores and causes

them to adhere to whatever they touch.

14
Often the fungus grows entirely tlii-ough the wall of a pod and

enters the seed, where it may remam alive, buried under the seed

coats, for months or even for years. When seed thus infected is

planted and germuiates, the fungus begins to grow and forms lesions

on tire cotyledons. From tliese lesions, infection may be carried to

the stem, other leaves, and pods.

The anthracnose fungus is very sensitive to changes in temperatiue

and humidity. It develops most abundantly in cool, wet weather and

largely disappears under hot, dry conditions.

The fungus may live over from one season to the next on old bean

vines in the field or in bean seed. It is not known just how long the

spores will sur\-i\e under field conditions, but apparently they can live

at least 2 years.

Controi

The most effective control measures for bean anthracnose are (1)

planting disease-resistant varieties, (2) using disease-free seed, (3)

rotating crops, (4) staying out of the field when the plants are wet, and

(5)^ spraying.

The only resistant variety now available to growers is Sanilac.

Disease-free seed can be obtained with certainty only from regions

where anthracnose does not occur, that is, from the Mountain and

Pacific States.

Where danger of anthracnose infection exists, it is advisable not to

plant snap or dry beans on the same ground oftener than once every

3 or 4 years.

Because spores of the anthracnose fungus adliere to clotliing and

machinery, it is not advisable to cultivate or pick beans, or to enter

beanfields for any other purpose, at a time wlien tlie plants are wet.

Within recent years these fungicide tieatments liave been reported

to have proved effective in reducing antliracnose infection :

Povnils pel- 100

Fungicide: tlfiUonn of Hjflter

Ferbam (Fermate; ferlierk ; ferradow : Karbam, black) 2

Zineb (Dithane Z-78, Parzate zineb fungicide) IVa to 2

Ziram (Zerlate; zirberk ; Karbam, white) 2

Ferbam and ziram slioukl not be applied to plants within 4 days of

harvest. Zineb should not be appliecl within 7 days of harvest.

See statement on page 2 regarding precautions to be taken in

using chemical fungicides.

Rust

Bean rust sometimes causes substantial losses in the East, far

West, and the South. In some years it has been one of the principal

diseases of dry beans in the irrigated areas of Colorado, Wyoimng,

and Montana. It has caused losses also in southern California, Oregon, Washington, Florida, Maryland, and other States. The fungus

causing this disease is greatly influenced by weatlier conditions. It

is favored by damp, rainy weather with cool nights. Consequently,

in some localities bean rust often appears only in the latter part of

15
the growing season or in tlie fall. However, occasional summer epidemics of the disease in bean-growing districts of the Mountain States

have been severe enough to destroy the entire crop.

Description

Bean rust is chiefly a disease of the leaves (fig. 9). Its first symptom is small white spots or flecks on the undersides of leaves. Withm

a few days these break open into rust-colored lesions of the type

FIGURE 9.—Rust is sometimes one of tlie principal diseases of dry beaus in

certain Rocky Mountain areas. Rust pustules, seen here on both upper and

lower surface of leaves, may cause defoliation of bean plants.

16
resembling pimples, called pustules, about the size of piuheads. These

lesions appear on both the \ipper and the lower leaf surfaces. As

many as 2,000 have been counted on a single leaf. A week or so after

the pustules appear, the entire leaf begins to turn yellow. Later it

turns brown, shrivels, dries up, and falls from the plant. Often a

seriouslj' infected beanfield looks as if it had been scorched.

Cause

Bean rust is caused by the ñuigus Vromycen jihaaeoU (Pers.) Wint.

var. typica Arth. This fungus reproduces by means of spores and

has several stages. Usually the grower notices onl}' the summer stage,

which shows up as reddish-brown pustules containing thousands of

reddish-brown spores. Tliese spores readily come off on the hands

and clothing of anyone touching the plant. In this way, and also

through wind action, they spread from plant to plant and fr'om field

to field. Toward fall the rust produces a ditferent kind of spores.

They are black and very hardy and live o\'er winter, principally on

old bean straw. A few of the summer spores, also, live over winter.

The fungus is not known to live more than 1 year and is not seedborne.

Eust gets a start in beanfields principally when growers plant lieans

on land where beans were infected with rust the preceding year. This

is particularly risky where beans have lieen harvested with a combine

and the infested straw has been left in the field and not plowed under

until late the following spring. Rust spores on the straw germinate

in early spring and infect the new crop.

Control

Methods for control of bean rust include dusting with sulfur, maneb,

or zineb; rotating crops; and planting disease-resistant bean varieties.

At present, the most effective of these methods is dusting with

fungicides.

If finely ground sulfur (about ?âr> mesh or finer) is dusted on beans

in suitable quantitv early in the season, before any rust spots become

noticeable, this treatment effectively protects the crop from rust mfection. The sulfur destroys rust pustules present at that time, which

stop spreading of spores from such spots, and thus prevents formation of other spots. If dusting is done after the rust infection has

spread widely m a field, it must be repeated and even then does not

give complete control. About 20 to 25 pounds of sulfur per acre

should be used in each dusting. Spraying or dusting with maneb

or zineb is also effective in controlling the disease.

If beans are planted on land that produced a crop heavily mfected

with rust the preceding year, the new crop will become infected

earlier in the season and more severely than it would have under other

conditions. Infested bean straw should be used for feeding or bedding livestock. „

All the common dry bean varieties are susceptible to rust. JNone

of the bush snap bean varieties are resistant to rust, but most are

highly tolerant of most strains of the organism. Recently a new

strain has been found in parts of eastern United States aflectmg

fall-grown beans. Most varieties are susceptible to this strain, except

17
Seminóle, Tenderwhite, and Tennessee Green Pod. Some of the

common pole snap ]jeans, snoh as Blue I^iake, McCaslan, and Kentucky

AVonder, are very susceptible to rust. Tolerant pole varieties include

White Kentucky Wonder, U.S. No. 3 Kentucky 'Wonder, Potomac,

and Rialto.

Watery Soft Rot

Watery soft rot, or white mold, is an economically important disease

of beans in several parts of the United States. In certain years it

has caused heavy losses in beanñelds of southern Florida. It is serious

also in the bean-growing sections of Colorado, Wyoming, Idaho, and

Montana, and on snap beans in western Oregon.

High humidities and fairly cool temperatures are necessary for

development of the fungus that causes watery soft rot. In irrigated

beanfields, heavy vine growth keeps the plants moist for rather long

periods, and this permits the fungus to become active. The fungus

develops best between 60° and 70° F.

Description

Watery soft rot of beans affects the stems, leaves, and pods. It is

illustrated in figure 10 and on the cover of this handbook. Small

soft, watery spots appear first. Under cool, moist conditions these

spots enlai'ge rapidly. Often they girdle main stems and branches,

causing them to wilt and die. An infected pod soon turns into a

soft, watery mass. Often a sticky brown liquid exudes from the

pods and stands on them in small drops. After the watery stage

the affected tissues dry out, becoming light and punky.

Within a day or two after infection, dense masses of white mold

grow out over the infected spots. These white masses have the appearance of small patches of snow. Soon they turn light gray or

brown, and small hard, black bodies called sclerotia, resemblmg bits

of charcoal, appear within them. Mold on infected bean pods in

shipping baskets causes the pods to nest, or stick together.

Bean seeds attacked by the fungus causing watery soft rot become

dull and chalky in appearance and are lighter in weight than normal

seeds.

Cause

Watei'y soft rot is caused by the fimgus Sclerotinia sclerotiorum

(Lib.) DBy. The black sclerotia formed in the mold fall to the

ground. When moisture conditions and temperatures are favorable

for fungus growth, strands of white mold may then grow out of

these bodies and infect bean plants directly. Infection in this way

is fairly common, particularly when the plants are young. If conditions are not favorable when the sclerotia fall to the ground they

can remain in a resting stage for a considerable period—sometimes

as long as 10 years.

Infection takes place also by means of spores. From the sclerotia

grow very small bodies resembling mushrooms, each of which may

produce many thousands of spores. These spores are thrown forcibly

into the air. If blown to nearby bean plants, they germinate on

18
any dead plant parts—such as old blossoms, stems, or leaves—and

proceed to the growing tissues. Soon new masses of mold appear,

and in these more sclerotia are formed. Since eacli sclerotium is

capable of producing a large number of the spore-bearing bodies and

each of these bodies may produce many thousands of spores, even a

few sclerotia in one field can soon cause widespread infection in several

adjoining fields.

FIGURE lO.-Pods in an advanced stage of watery soft rot.

19
The sclerotia ave capable of ]i\iiig over from one .year to another

in the soil and thus perpetuating and increasing the infection.

Just how watery soft rot can get a start in a locality is not definitely

known. Possibly spoi-es are blown through the air for considerable

distances. Appai'ently, infection can be carried by the slightly infected seed that survive in some infected bean pods. It is possible

for a few of the sclerotia to become mixed in seed lots and thus pass

from one locality to another unnoticed. In the seed-producing areas

of the far West the use of combines, feeding of straw to sheep, and

later use of manure sometimes spread the sclerotia. Another likely

way of spreading the fungus to new fields and farms is the practice

of feeding cull beans to sheep.

Control

Xo bean varieties are known to be resistant to the fungus causing

watery soft rot, and no spray or dust materials have been found to

control the disease effectively. There are, however, several practices

that can usually be depended on to reduce the losses caused by the

disease.

A high percentage of the sclerotia can be destroj'ed by flooding infected fields for periods of 3 weeks or more. In preparation for

flooding, all plants—including weeds and grasses—should be cut down

so they will be covered by the floodwater. Because high temperatures

hasten decay, the best season for flooding is summer.

Broadcast applications of calcium cyanamide at the rate of 1,000

pounds per acre have given very good results on some soils. The

cyanamide should be cut in with a disk harrow to a depth of about 3

inches, and beans should not be planted on the treated area until

about fiO days later. Cyanamide injures germinating seed; therefore it must be broken down through natural chemical action in the

soil before the treated area becomes safe for planting.

Since high humidity favors watery soft rot, any method of bean

culture that reduces the amount of moisture in the surface soil and

air around the plants aids in controlling the disease. A field where

the disease is found should not be irrigated more often than necessary.

Wider spacing of rows and reduced rates of seeding, which prevent

the vines from meeting early in the season and allow better air circulation, are two other methods for reducing the moisture around the

plants and thus cliecking development of the rot fungus.

Many weeds, such as ragweed and milkweed, are known to be susceptible to watery soft rot. If these are allowed to grow along

roads, ditches, and canals close to beanfields, they may become sources

of infection. Beanfields that have been abandoned because of infection should be kept free of weeds.

Infested bean straw and cull beans contaminated with sclerotia

should not be fed to animals if the manure is to be used on land where

beans may soon be planted. Screenings from bean cleaning mills,

which may contain large quantities of sclerotia, should be burned.

When possible, infested beanfields should be planted for 2 years

or more to crops that are not susceptible to watery soft rot. Such

crops include small gi-ains, corn, and hay. Wiile this is not likely

to eliminate the trouble entirely, it will reduce losses on beans to a

20
considerable extent. Likewise, beans sliould not follow otlier crops,

or weeds, that are known to have been seriously infected with the

fungus causing watery soft rot.

Powdery Mildew

Powdery mildew is more important in the Southern States and

along the Pacific coast than elsewhere. Usually it causes the most

damage to crops niaturing late in the fall and crops produced in the

extreme South during the winter.

FiGUEE 11.—Here powdeiy mildew, a fungus aisea.se that develop-s very rapidiy,

has readied a rather advanced stage. The bean crop could still be saved by

dusting with finely ground sulfur. If not dusted, the plants will lose all

their leaves.

Description

In powdery mildew, a white substance resembling powder is produced on all abovegromid parts of the plant (fig. ll). Leaves turn

yellow and, in extreme cases, fall off. Often pods are malformed,

small, and poorly filled and fall off before any seeds mature. Pods

and stems often turn purplish.

Cause

Powdery mildew is caused by the fungus Eryniplie polygoni DC.

The spores of this fungus, produced in great numbers on leaves,

pods, and stems, are easily dislodged and carried from one plant to

another either by wind or in some other way. Powdery milcle«

develops so rapidly that an entire bean crop may be badly damaged

within a few clays.

21
Control

Powdery mildew of beans can be lield in check by dusting the

infected crop once or twice with finely ground sulfur or Karathane.

The first application should be made as soon as any evidence of the

disease is seen. Tlie second should follow within a week or 10 days.

A variety of snap beans that resists one form of this disease may

be susceptible to another. Snap beans only slightly susceptible to

powdery mildew are Contender, Extender, Idalio Refugee, Seminóle,

Tenderlong 1.5, Topcrop, and Wade. Some of the very susceptible

varieties are Black Valentine, Bountiful, Kinghorn Wax, Landreth

Stringless Green Pod, Plentiful, and Tendergreen.

Root Rots

Parasites that cause root rot of beans exist wherever beans are

grown. They are more numerous and do more damage to the crop

in the South tlian in any other region of tliis country. Within recent

years some of them have become a serious problem in parts of the

West. Most of tliese parasites live in tlie soil on decomposed vegetable matter, and can attack bean plants whenever soil conditions and

weather become unfavorable for best growtli of tlie plants.

Description

Most of the parasites causing loot rot of beans form lesions of

various sizes on the stem below the soil level (fig. 12) and on the

fibrous rootlets. These lesions may be gra}', brown, black, or even

bright red. Frequently the parasites cause the tips of the fibrous

roots to decay. Some of these cause stunting and general yellowing

of the plant.

When root rot of beans is caused by Fusarhim fungi, usually a

reddish discoloration appears on the taproot. This discoloration may

extend to the soil line. The plants are stunted, and the leaves may

turn yellow. Sometimes the main root and the lower part of the stem

become pithy and dry. Usually the rootlets that develop from the

taproot are killed. In that case a cluster of rootlets develops above

the lesion, a little below the soil line. These rootlets keep the plant

alive, and if weather conditions are favorable an almost normal crop

may be produced.

In the type of this disease known as rhizoctonia root rot, bean seed

may rot in the ground before or during germination, seedlings may

be twisted and stunted, and reddish-brown cankers may form on the

roots and on the stems, particularly below or at the soil line. Often

these cankers girdle the stem. Young seedlings thus affected damp

off, that is, they rot at the soil line. Older plants may remain erect,

but they are stunted and their leaves turn yellow.

In the types of root rot known as pythium wilt and southern wilt,

the plant wilts suddenly and dies. Pythiimi wilt usually occurs only

on the stem, at the soil line. The affected tissue becomes soft and slimy

and can easily be separated from the central cylinder of the stem.

Sometimes the stem is girdled. T^sually the infection does not extend

much below the surface of the soil.

22
^fvNV.

FlQUKE 12,—Wherever beans are i^rown. fungi are ¡¡resent in the soil that can

cause their roots to rot. Dry root rot, illustrated here, is one of several different root rots of beans. The one effective method of control known is to give

beans the best possible conditions for vi.gorous .growth.

In southern wilt, bean roots and stems rot and become dry and

papery. A white fungus growtli develops on the stem at the soil line

and spreads into the soil around the plant. If the plant is pulled out

of the soil, a collar of soil and fungus mycelium clings to it.

Cause

The most common of the fungi that cause root rot of beans are

Rhizoctonia solani Kuehn, Fusarhim Holani f. phaseoli (Burkh.)

Snyd. & Hans., Pythium hutleri Subr., and Srlerotium rolfsii Sacc.

The Fumr'mm fungus causes dry root rot, and the Sclerotium fungus

causes southern wilt. All these four except F. aolani f. phafieoli cause

root rot of other crops. All can live for long periods in soil where

no cultivated crop is being grown. The Rhizoctonia fungus very

commonly attacks potatoes. Koot-rot fungi are normally present in

practically all soils.

Root-rot organisms, with the exception of Sclerotium rolfsii, are

favored by cool weather and high soil moisture content.

Control

No effective method is known for controlling the various root-rot

fungi. No bean varieties are resistant to any of them. HoAvever,

these fungi seem to thrive least well under conditions that are ideal for

23
bean crops. The Rhizoctonia fungus, in particular, is not aggressive

vmder conditions that favor production of strong, vigorously growing

bean plants ; where the soil is warm and the seeds are planted shallowly,

it does little harm. Therefore, everything that the grower can do to

make conditions favorable for his beans tends to make them unfavorable for these ¡larasites. A rotation of at least 4 or ñ years is recommended. Tlie cropping system should include cereals (corn, oats, and

others), clover, and alfalfa, plants to which the fungi causing root

rot of beans rarely or never do any lasting damage.

Root Knot

Root knot, a bean disease found chiefly on the light sandy soils of

the South and on similar soils in California, prevents bean plants

from deieloping normally, and may e\'eu kill them.

Description

In root knot, fleshy, iriegular-shaped galls are produced on bean

roots (flg. 13). Root-knot galls may sometimes be confused with the

nodules that normally develop on the roots of snap and dry beans,

lima beans, and other legumes. The galls can easily be identified,

however, because they are enlargements of the roots themselves,

whereas the nodules are attached rather loosely to the sides of roots.

The galls are usually larger than the nodules and are more irregular

in shape. The bacteria that cause formation of the nodules change

nitrogen of the air into forms that are beneficial to the plant. Therefore, plants bearing root nodules generally grow well and look healthy.

Plants with root knot, on the other hand, are usually stunted, yellow,

and sickly looking.

Cause

Root knot is caused by several species of parasitic nematodes, or

eelworms, called Meloidogyne spp., so small that they can hardly be

seen with the unaided eye. The females of this nematode—or nema,

as it is commonly called—enter the small roots and cause them to form

the galls characteristic of the disease. If one of these galls is broken

open, often a pearl-white body smaller than a pinliead can be seen

within it. This is the worm that caused the gall. The galls seriously

interfere with mo\-ement of food material from the roots to other parts

of the plant. The nematodes migrate very slowly in the soil, probably

not covering more than 1 to 2 yards in a year. Thev overwinter in the

soil.

Con/ro/

The root knot nemas are parasitic on many cultivated plants and

on many weeds. This fact makes it very hard to control them.

Plants immune to them include beggarweed, crotalaria, oats, and rye.

Where soil has become infested with the nemas, growing any of these

plants for 3 years makes it possible to grow beans again successfully.

One resistant snap bean variety is the pole bean Alabama No. 1.

The more vigorous a bean plant is, the better chance it has to escape

severe damage by nematodes. In many instances a bean crop can be

24
saved from such damage by fertilizing the soil and providing the

plants with plenty of moisture. Clean cultivation should be practiced

in nematode-infested beanfields to keep down weeds on which the

nemas could feed.

If beans must be ]5lanted on land infested with root knot nematodes,

it is advisable to fumigate the soil with some such preparation as

dichloropropenedichloropropane (commonly known as Shell DD or

Dowfume N), ethylene dibromide, or metliyl bromide. Such treatment often improves germination and growth and increases yields.

FioURK 13.-Root knot. Each gaU on these bean '-""ff;;;;"^^«;;;^^,','f^,,,"! [

more nematodes. or eelworms, that entered the "»' ^"'^J,?''^'„'' líe,"

Root knot prevents plants from g.-owing normally and may kill

25
Anyone using one of these fumigants shovild be careful to follow the

instructions given by the manufacturer.

See statement on page 2 regarding precautions to be taken in

using fumigants.

So far as ]5ossible, bean growers should guard against the carrying

of root Icnot nematodes from one field to another in tubers, bulbs, or

roots of living plants, on implements, in drainage water, by roaming

farm animals, or in any otlier way.

Ashy Stem Blight

Ashy stem blight, a bean disease now common in the South along

the Atlantic seaboaicl, and in California, sometimes cau.ses very large

losses. This disease is serious in seasons of rather heavy rainfall and

high temperatures. In dry seasons it often disappears.

Description

Infection with the fungus causing ashy stem blight begins on the

bean stem at or below soil level. It extends down into the roots and

also up into the branches. The lesions on young plants are somewhat

sunken and have a reddish-brown color. As a lesion enlarges it turns

ash gray at the center. Numerous black fruiting bodies, about the size

of a pinpoint, appear at the center, standing out in sharp contrast

against the gray background. Infection usually takes place on a

young plant, and an infected plant usually dies before it produces

seed. If infection is delayed until the primary leaves are fully developed, the fungus makes slower progress. On an older plant, the

lesions are only a little sunken, if at all. Frequently the disease is

more j^ronouneed on one side of the plant, causing the primary leaf

on that side to droop and die and any remaining leaves to turn yellow.

Cause

Ashy stem blight is caused by the fungus Macrophomina fhnseoli

(Maubl.) Ashby. Many spores are produced in the black fruiting

bodies of the stem lesions. Tlie fungus is seedborne. Apparently,

also, it lives over from one season to the next on plants left in the field.

Confrof

No control for ashy stem blight has been developed. Since the

fungus causing the disease is seedborne, no beans of an infected crop

.should be used as seed. A 2- or 3-year rotation with crops other than

snap or dry beans, lima beans, and sweetpotatoes is advisable.

Angular Leaf Spot

A bean disease called angular leaf spot occurs occasionally in the

Eastern and Southern States. It reduces the vitality of the plants

and lowers yields, but usually it does not cause serious losses.

26
ûescriplion

The small spots described by the name "angular leaf spot" are

brown at first, but when the fungus causing tlie disease fruits they

become more or less gray. Sometimes tliey are numerous enough to

cause leaf fall. The spots on the pods are usually small, but are sometimes large and conspicuous and may run together across the whole

whole width of the pod.

Cause

Angular leaf spot is caused by the fungus Isariopsis griseoln Sacc.

Spores produced, on the undersides of leaves, in the lesions caused by

this fungus are scattered by wind and rain, and in this way new infections are caused.

Control

Angular leaf spot is rarely severe or common enough to require

control. Infected plants have been sjirayed witli a 4—l-,iO bordeaux

mixture, but without well-defined results.

Web Blight

Web blight has caused serious losses of beans in Florida over a

period of several years, and has been reported on beans in otlier

soutliern States.

Description

The Aveb blight fungus produces small round water-soaked spots on

bean leaves and mycelial growth resembling spider webs on bean stems,

pods, and leaves. Many small brown sclerotia are imbedded in the

mycelium. The spots on leaves are much ligliter in color than the

healthy tissue and look as if they had been scalded. They take on a

tan color, and dark borders form around them. On young pods the

spots are light tan and irregular in shape. On mature pods they are

dark brown and sunken. In some cases the lesions look very much

like those of anthracnose. Sometimes they run together over an entire

pod. In the later stages of the disease, if the weather is favorable,

the mycelium spreads to all parts of the plant and binds leaves,

petioles, fiowers, and pods together.

Couse

Web blight is caused by the fungus BUzoctonia m-icrosderotia

Matz, which is parasitic not only on beans but also on tomatoes, beets,

eggplants, cucumbers, carrots, and other vegetables. Under favorable

conditions the small, light sclerotia of this fungus may be produced in large numbers. They are readily detached from the diseased plants and may be scattered by Avind and rain, by bean pickers,

on farm implements, and in otlier ways.

27
Control

To reduce losses from web bliglit. the bean grower should avoid

planting beans in ñelds where the disease has recently occurred,

especially during rainy periods. He should rotate beans with crops

such as tobacco, corn, and grasses, which are immune to the disease.

To prevent accumulation of sclerotia in the soil he should destroy

diseased plants as soon as possible after harvest. Where the disease

has appeared, spraying with a 3-3-50 bordeaux mixture is

I'ecommended.

For precautions to be taken in handling bordeaux mixture, see

page 2.

Baldhead

Description

When a crop of liean seedlings has jusf emerged from the ground,

the grower often finds that many of them look like those in figure 14.

These seedlings have no growing tips. The stem above the cotyledons

is only a bare stump. Sometimes this stump grows till it extends

an inch or more above the cotjdedons. Occasionally the plant dies

without making much more growth; usually, however, new shoots

develop in the axils of the cotyledons and produce a few flowers and

pods. The plant always remains small, and usually it is smothered

and crowded out by more vigorous neighboring plants. This abnormality is known as baldhead.

Cause

Baldhead results from meclianical injury to seed or from attack on

seed by insects, bacteria, or fungi. Possibly the most common cause

is improper threshing, which may damage as much as 20 or 30 percent

of a crop of some liean varieties. Frequently threshing damage

leaves no visible mark on the surface of the seed. The drier the seed

and the greater the speed of the threshing-machine cylinders, the more

severely beans are likely to be damaged in threshing. Injury to bean

seed may result, also, from improper handling in milling, cleaning,

storing, or shipping, particularly if the beans do not contain much

moisture. AVhen cup elevators in warehouses are emptied, for example, the contents of the cups are thrown with considerable force,

and when beans are delivered to storage bins they frequently roll

down a series of slides, sometimes 15 feet long, from one side of tlie

bin to the other. At the end of each slide, the beans strike the wall

and may receive a severe impact. After beans are bagged, they may

be injured by being thrown or dropped onto a hard surface.

Control

To avoid losses from baldhead, bean growers should refuse to accept seed of which a high percentage is cracked. To avoid damage

to bean seed, threshing-machine cylinders should not be operated at

high speed and the iron teeth of the cylinders and concaves should

be covered with rubber shields or else replaced with teeth of some

28
substance not so hard as iron. Other measures for preventinfi interiuü injury of seed that might residt in baldliead are iniproviuf;

warehouse equipuient to prevent dropping seed too far and liandliu!;

seed more carefully after it is bagged.

%

FiGuiiE 14.-Seecllings without normal gi-ONYing tips are t'i'? ^«'f ^^^"¿¡^''ift; "j,,

expected to develop from damaged seed. Baldhead, ?" ,'^;„^,4''tTttae,Mng

called, commonly results irom cracking of seed in «/«P'^'J,X smo nerefout machine. The plants never grow to normal size and are usually smothered

29
Sunscald

When beans have almost reached maturity, sunscald lesions (fig. 15)

are likely to appear on any parts directly exposed to the sun. The

fresli lesions are tiny brown or reddish spots, which show up most

conspicuously on the pods. There they develop into short streaks

extending diagonally between the sutures. In early stages the lesions

look so much like those of bacterial blight that many of them cannot

be identified without a microscope. Latei' they can be identified without much difficulty, because nothing resembling bacterial ooze is present in sunscald.

FIGURE 15.—Brown or reddish lesions may appear on bean pods as a result of

long-continued direct exposure to sunlight. These lesions, called sunscald,

are sometimes contused with those of bacterial blight.

30
The spots or streaks gradually grow larger and sometimes become

slightly sunken. A single lesion may extend over most of the exposed

part of a pod. Spotting may finally appear on the shaded side of

a pod, but there it is never so serious as on the surface exposed to the

sun. Sometimes brownish-red streaks are seen on shaded stems and

petioles.

Sunscald of beans causes no substantial loss. Occasionally, seed

in badly spotted pods become slightly discolored, like those in pods

affected by bacterial blight. The seed discoloration is often hard to

detect, particularly on naturally dark seed. It does not prevent production of normal, viable seed.

No practical method of controlling sunscald is known.

DISEASES OF LIMA BEANS'

Downy Mildew

Description

Don^ny mildew may cause heavy damage to lima bean crops during

any season favorable for development of the causal fungus. The

fungus producing this disease is favored by wet weather with cool

nights, heavy dews, and fairly warm days. It is spread by wind,

ram, and pickers, and probably also by insects and other means. The

disease is most common along the Atlantic seaboard.

Downy mildew of lima beans can be recognized by the white, cottony growth that forms in large patches on the pods (fig. 16).

Patches of this white grow-th on tlie pods are separated from surrounding healthy tissue by purplish borders. Frequently the downy

mildew fungus attacks not only pods but young leaves, shoots, ana

flower parts. Irregular-shaped purplish discolorations often appear

on the infected leaves, especially near tlie veins, without^much visible

mycelium. Under conditions ideal for development of the fungus,

the leaves are killed and the pods shrivel, wilt, and slowly die.

Cause

Downy mildew is caused by the fungus Phytophthora phaseoli

Thaxt., which attacks lima beans only. The fungus penetrates seed

and lives in them throughout the winter. It also lives over winter

on dead vines and pods in the field. Both the seed and the dead plant

material are sources of infection of the new crop.

Control

The most satisfactory control of downy mildew is the use of resistant

varieties. Thaxter, an Early Thorogreen type, is the only variety

resistant to the disease. . ., i i^„„, „

Growers of lima beans should carefully avoid using seed from a

crop infected with the fungus that causes â°^^ny ^^f^'^;, Í^^,-wp

practice is to use seed produced in some area m the tar VV est, wnere

downy mildew rarely if ever occurs, and to grow the »3^*"^ °? ^ f

or 3-year rotation. Maneb and basic copper sulfate aie fe^-ti;« ¿^

controlling the disease. Other chemicals such as Phaltan and Dyi ene

»Two of the diseases discussed only in this section, seed pitting and stem

anthracnose, occur also on snap and dry beans.

31
,^

:> '■■) 5?\

_. «••

^^Wlv

Éê * \ .i «pw»^"--~..

MM^K "^"''^ '"^"S; ^#^^Ä Z "X'i%à

.;>

"^"^

"\

FKíURí-; 1(1—Downy iiiildt^w. a fuii^u« disease nf lima lieaus. causes heavy losses

ill wet seasons. The outstanding symijtr)m is a w-hite growth that appears

on pods and also on young leaves, shoots, and flowers.

are also satisfactory. Tlie copper sprays liave been reported to cause

some foliage and pod injury. Because the disease does not occur

regularly every year, it is hard to determine when to apply fungicides.

For precautions to be taken in handling maneb and other copper sprays, see page 2.

Pod Blight

Pod blight of lima beans has been reported from most of the States

along the Atlantic seaboard and from Ohio and West Virginia, and

it probably occurs elsewhere. During seasons favorable to it, the pod

blight fungus causes considerable damage to the conmiercial crop.

Descripfion

Tlie ñrst symptom of pod blight is brown patches of irregular shape

on the leaves. Often these develop to diameters of one-fourth to

three-fourths of an inch. During the latter part of the growing

season the fungus spreads to the pods, where it causes pale, somewhat

watery-looking spots. These spots slowly enlarge and gradually

darken (fig. 17). Within the blight spots on pods and leaves appear

32
FIGURE 17.—Lima bean pods affefted by pod blight. Witbiii the large le.sions

are small dark spots containing siïores. The fungus causing the disease

spreads by means of spores produced on pod.s, leave.s. and stems.

greenish-gray pustules about the size of a pinpoint, arranged roughly

in circles. "Wlien the pustules break through the surface of a leaf

or pod they turn dark brown, sometimes nearly black. Such pustules

occasionally appear on the stem of the living plant.

Cause

Pod blight is caused by the fungus Dkiportlie phaseolonim (Cke. &

Ell.) Sacc. This fungus spreads by means of spores produced within

pustules on bean pods, leaves, and stems. It lives over Avinter on

dead vines and pods left in the field. It has been found also on the

seed.

Control

Little effort has been devoted to the control of pod blight. Wherever danger of the infection exists, it is recommended that tlie plants

be sprayed with 4-4^50 bordeaux mixture from the time they are

about 2 feet tall. After the crop is harvested, dead vines and pods

lying on the ground should be gathered up and burned. Lima beans

grown in fields where pod blight has recently occurred should never

33
be used for planting. Planting of lima beans shonkl be done with

seed i^roduced in the far West.

For precautions to be taken in handling bordeaux mixture, see

page 2.

Bacterial Blight

^ Bacterial blight of lima beans may occur in all parts of the united

States «here rain falls fi'equentlj' during the growing season. It

does greatest damage along the Atlantic coast and in the South. It

occurs frequently in the Midwest but usually causes almost no reduction in yield there. The term "bacterial blight" applies to three

diseases of lima beans—common blight, halo blight, and bacterial

spot.

Description

Bacterial blight occurs on the leaves, stems, and pods (figs. 18 and

19). Tlie symptoms of common and halo blights on lima beans

closely resemble those on snap and dry beans, and the leaf symptoms

FiGUBE 18.—Bacterial spot on lima bean leaf.

34
FiGUHE 1!).—Lima bean pods Hlutwiriíí infectiüii iA ) with coimiioii blight anil (/Í)

witli Ijac'terial siiot, wliicli t-auses smaller lesiiins.

of bacterial spot on lima beans resemble those of the two other bliglits.

In general it is very hard to distinguish one of these blights from

the others without laboratory tests. In early stages of infection

common and halo blights cause water-soaked lesions. In bacterial

spot the lesions are not watery and are more regidar in outline and

usually smaller than in common or halo blight. A band of reddishbrown color near tlie edge of the leaf lesion is very characteristic

of bacterial spot. As tlie lesions enlarge their centers turn light

gray and become dry and papery. The dry, dead centers of lesions

often fall away, leaving small holes.

Cause

Common blight is caused by Xa.nthomonas phiiseoH (li.F.Sm.)

Dows. ; halo blight, by Pseudomonas phaseolicoJa (Burkh.) Uows. ;

bacterial spot, by P. xyringae Van Hall. These bacteria spread iery

rapidly from infected plants during heavy rains and hailstorms.

Control

To reduce the danger of damage to a crop of lima beans from

bacterial blight, the seed should be obtained from some area m

the far West where blight epidemics do not occur. It is unwise to

plant lima beans again on ground where a recent crop has been infected. The rotation should not include snap beans, dry beans, cowpeas, or soybeans, since each of them is susceptible to one or more

kinds of blight.

Seed Pitting

Seed pitting, often called yeast spot, spoils many a crop of lima

beans in some seasons.

35
Fim-RE 20.—Seed having (lark sunken lesions are sometimes found In lima bean

pods that look entirely healthy. The seed pitting is caused by insects and

possibly liy a yeast that enters through punctures made by insects.

Description

Each of the affected beans lias one or more dark, wrinkled spots,

irregular in shape and somewhat sunken (fig. 20). Occasionally the

seed coat breaks. In that case, craterlike lesions develop on the

cotyledons. Pitting may take place on beans at any stage of growtli,

but injures them most severely if they are less than half grown.

Seed infected at an early stage sometimes fail to develop beyond

one-tenth of normal size and often die prematurely. However, they

sometimes develop to natural size. No sign of disease appears on tlie

outside of the pod even when the seed are badly pitted.

Cause

Seed pitting of lima beans is reported to be caused by the yeast

Nematonpora phaseoli AVingard, which enters through punctures

made by the southern green stink bug (Nezara viridula (L.) ) and

probably other insects.

In California and Idalio seed pitting very similar in appearance

to that attributed to Nematospora phajseoli, if not identical with it,

results from activity of two lygus bugs {Lygus hesperus Kngt. and

L. elisus Van Duzee) and, possibly, other insects. These bugs poison

the bean plant as they feed, with the result that the plant sheds its

blossoins or young pods.

Confro/

No control measures for the yeast spot type of seed pitting have

been developed. The large Fordhook lima bean is reported to be

less susceptible tlian the small sieva type.

Five-percent DDT has been found by several workers to be effective

in controlling the two lygus bugs mentioned. Field experience in

California suggests that growers of lima beans should carefully

avoid planting limas next to perennial plants such as seed beets and

alfalfa, which are favored by these insects.

36
Insecticides are poisonous. Handle tliem with care. Follow

the directions and heed all precautions on the container label.

Do not feed DDT-treated bean plants to dairy or meat animals.

Stem Anthracnose

Stem anthracnose occurs on lima beans (and also on snap beans)

chiefly in the Southern and Eastern States. In the South, field losses

of 5 to 10 percent of a crop of lima beans from this cause are not

uncommon in some years. Further losses have been reported after

affected lima beans reached wholesale markets.

Descrípríon

Stem anthracnose of lima beans affects the stems, leaves, pods, and

seed (fig. 21). A brick-red color is produced along the veins on the

underside of the leaf and on the young succulent parts of the stem

and petiole. Irregular, rough, elongated cankers may appear on

the stem. On tlie pod the first signs of infection are small reddish

blotches, which may spread over the entire surface. In later stages

of the disease the infected areas become light brown or grayish and

numerous black bodies appear on them. Severe infection dAvai-fs the

plant and causes marked yellowing of the leaves. Not unconmionly,

the affected foliage droops and the plant dies.

Cause

Stem anthracnose is caused by the fungus GoUetotrichum trimoatum (Schw.) Andrus & W. D. Moore. Characteristics of this fmigus

ri«UEE 21,-Stem anthracnose of lima beans: fv^-^f '" ^^.«"ToL'''''^^' "' the disease ; B, leaf displaying lesions on both blade and ijeuoie.

37
are the same as those of C. Undemuthianuin, already discussed as the

cause of bean anthracnose.

Control

To control stem anthracnose of lima beans, the grower should use

non infected seed and should rotate other crops with the beans. There

are no resistant varieties available. Several spray applications of

Maneb and Dyrene have proved very effective in controlling the

disease. Growers should consult their county agricultural agents

or State agricultural colleges as to tlie concentration of the sprays and

number of applications that have proved most satisfactory under

local conditions.

DISEASES OF BEANS IN TRANSIT AND STORAGE

Nearly all the known diseases occurring on beans while they are

being shipped or held in storage arise from conditions existing in

the Held befoi-e or during harvest. Under hot, humid conditions

FlGUBE 22.—These siiaii beans, grown in the South, were held graded and shipped

to a northern niaricet without refrigeration. In transit, they W'ere ruined

by anthracnose.

38
FIGURE 23.—Híiutlierii-growu siiay beans, rteld sji-adecl and sliiiiped nnill] Hillmut

refrigeration, that were made wortliless on the way by watery soft rot.

anthracnose, watery soft rot, and some other diseases develop appreciably on beans and sjoread from pod to pod dnring 4 or 5 days in

transit. If bean pods have become infected with root rot fungi wliile

in contact with soil in the field and are shipped or held at market

under high temperature and liumidity, the rot infection is likely to

spread from them. Bacterial blight can advance from stage to stage

but, apparently, blight bacteria cannot spread in shipments of beans.

Beans should be picked only wlien tlie vines are dry. They should

then be carefully graded, and all those showing blemishes and disease

spots should be discarded. The tilled hampers should be protected

from the direct rays of the sun and from dampness. Preferably, tlie

beans should be cooled before shipment and should be shipped in iced

cars. If this cannot be done, they should be sliipped as quickly as

possible in hampers so packed that the beans are exposed to the air as

much as they can be without danger of spilling beans or breaking

hampers.

The fact that grading alone cannot prevent complete loss in transit

of beans from a crop infected with anthracnose is illustrated in figure 22. When preparing these beans for shipment the graders tlirew

out all the pods on which they saw any sign of infection. A few days

in transit from South to North permitted hidden infection to spread

throughout the hamper. In such a case every hanipei- is sure to include

a few infected pods, and unless the shipment is refrigerated the infection is sure to spread rapidly in transit. Before the beans shown m

figure 23 were shipped, the graders threw out all the pods on which

they could see any sign of infection with the fungus causing watery

soft rot, which was known to be present in the crop. Again, because

the shipment was not refrigerated, infection that had not been

detected by the graders destroyed the value of the beans m transit.

39