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Identifying and Managing

Common Vegetable

Diseases in Your Garden

Amy Timmerman – Extension

Educator, Holt/Boyd County

Know How, Know Now

What Size are Plant Pathogens?

Nematode

head

bacterium

Plant

cell

Plant

cell

nucleus

fungus viruses

Common plant

pathogens and

their size relative

to each other

and to a plant

cell

Viruses

To small to been seen with a light microscope

Plants are stunted, chlorotic, and may not produce seed

Transmitted by aphids, mites, beetles, other insects, nematodes and fungi

Tomato spotted wilt virus

Kansas State Research and Extension

Squash Mosaic Virus

Bacteria

Single-celled

organisms

An opening is

required for infection

to occur

1st seen is a water

soaked spots that will

turn necrotic

Fungi

Most fungi require free

moisture to infect the

plant

Does not need

openings in the plant to

cause infection

Largest group of

pathogens that we

manage

Nematodes

Microscopic worm-

like animals

Feed on roots and

above ground parts

Roots become

distorted, bottle

brushed or galled

after feeding

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Disease System Components

environment

host pathogen

environment

85%

TIME

host pathogen

Disease System Components

Symptom Distribution

Field-Plant-Leaf Scale

Symptom Distribution – Field

Symptom Distribution – Plant Symptom Distribution – Leaf

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Cucurbits Bacterial Wilt

Dull green patches

appear on damaged

leaves

Entire leaves and

petioles wilt and

progress to entire

plant

Fruit may be wilted,

small, poorly shaped

poorly flavored

Penn State

M.P. Hoffman

Insect management reduces disease

incidence (bacterium overwinters in the insects

and plant material)

Remove and discard infected plants in the

garden

Resistant varieties (Watermelons are immune

and certain winter squash are resistant to this

disease)

Bacterial Wilt - Management

Leaves

Light, water-soaked or pale

green spots

Spots to enlarge to angular

gray-to-white spots

Tissue in the spots tears

easily

Fruit

Gray, slightly sunken spots

Gummy plant sap may exude

Spots become darker with

age

Scab of Cucurbits

T.A. Zitter

Use disease-free seed

Grow plants in warm locations with good air

and soil drainage

Avoid overhead irrigation

Scab - Management Powdery Mildew

White, powdery fungal growth

on both leaf surfaces,

petioles and stems

Yellow spots may form on

upper leaf surfaces opposite

of mildew colonies

Infected leaves usually wither

and die

Plant may senesce

prematurely

Fruit infections are rare

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Tomatoes

Small, brownish lesions

initially forms on foliage

Yellow halo surrounding

lesion

Lesion enlarges rapidly

to form concentric rings

Fruit lesion have

concentric rings and

may be covered with a

mass of black spores

Early Blight

Cornell University

Septoria Leaf Spot

Initially small, water-

soaked circular spots

on the underside of

older leaves

Dark brown margin

with a gray or tan

center

Spots may coalesce

Tiny black specks

present in mature

spots

Anthracnose

Small, circular

indented spot in the

skin on fruit beginning

to ripen

Enlarge to ½ inch and

becomes sunken

Center becomes dark

in coloration or

concentric rings of

dark specks develop

Early Blight, Septoria and

Anthracnose - Management

Pathogen-free seed/transplants

Resistant cultivars

Good air circulation

Remove infected tissue and fruit

Avoid overhead watering, otherwise water

in the morning

Maintain a balanced soil fertility

Late Blight

Cornell University

Kent Loeffler

Leaves

◦ Indefinite, water-soaked

spots

◦ Enlarge rapidly into pale

green to brown lesions

◦ Moldy growth observed on

around the underside of large

brown lesions

Fruit

◦ Dark, olivaceous, greasy spot

◦ Enlarge to cover entire fruit

◦ Soft rot

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Dispose of infected plants/fruits

– Do not make cull piles

Destroy volunteer tomatoes and

potatoes

Scout regularly for early

detection

Fungicide sprays at label rates

and intervals

Late Blight - Management Bacterial Spot

Symptoms on leaves

and stems

Circular to irregular

shape up to 1/8 inch

Similar to septoria leaf

spot – no grayish brown

center

Yellow halo surrounds

spots

Bacterial Spot

Symptoms on fruit

Green fruit susceptible

Initially starts as water-

soaked spot

Enlarge to 1/8-1/4 inch

Gray-grown in

coloration

Scabby with sunken

pitted centers

Bacterial Speck

Foliar

Small 1/16-1/4 inch

black spots

Slightly raised

Yellow halo

Fruit

Young, green fruit

Slight raised 1/32-1/16

inch diameter spot

Superficial

Bacterial Disease Management

Good sanitation in the fall and

during the growing season

Rotate position of tomatoes in

garden – avoid planting pepper in

the same area as tomato

Avoid overcrowding

Water at the base of the plants –

soaker hoses when possible

Purchase disease-free seed and

transplants

Virus Infected Tomato Fruit

Several different

viruses can result in

this appearance:

Tomato Bushy Stunt

Tomato Mosaic

Tomato Spotted Wilt

Eggplant Mosaic

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Virus Infected Tomato

Tomato Bushy Stunt Virus Tomato Spotted Wilt Virus

Cloudy Spot

Tomato

Viruses of Tomato

Tomato bushy stunt virus Mechanical readily;

vector unknown.

Tomato spotted wilt virus Thrips; sap

Tobacco streak virus Thrips; sap

Tomato ringspot virus Nematode (Xiphinema);

sap

Eggplant mosaic virus Flea beetles and contact

Cucumber mosaic virus Aphids; sap

Peppers

Anthracnose

Ohio State University

University of Florida

As fruit ripens,

susceptibility increases

Initial symptoms are

indefinite tan lesions

As lesions grows,

concentric black rings

may form

Anthracnose - Management

Planting pathogen-free

seed/transplant

Sanitation – remove

infected fruit

Pick fruit frequently

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Bacterial Leaf Spot

Necrotic spots on leaves, stems

and fruit

1st starts as water soaked areas

on underside of leaves

Enlarge to ¼ inch, turn dark

brown and slightly raised (lower

side)

Upper surface – depress with a

brown border around a beige

center

Leaves yellow and drop

Fruit spots are raised and

scablike

Bacterial Leaf Spot - Management

Plant disease

free seed and

transplants

Crop rotation for

at least 1 year

rotation between

tomato or

pepper

Beans

White Mold

Fungal disease caused by Scelrotinia

sclerotriorum

Symptoms are 1st visible

approximately 1 week after full

bloom

Initially tissues are pale colored and

water-soaked

Lesion enlarge to become covered

with a white, cottony growth

Sever infections causes leaves to

turn yellow and eventually brown

and fall off

White Mold Management

Moisture is critical – avoid

intensive irrigation around

flowering

Plant rows in the direction the

wind prevails

Avoid high plant populations and

narrow row spacing

Working the soil after harvest to

bury inoculum

Rotate crops in garden space

Resistant varieties are available

but are limited

Bacterial Brown Spot

Initial symptoms are small

water-soaked spots

Spots develop into

distinctive necrotic brown

spots about 3-8 mm in

diameter with a narrow

diffuse yellow margin

Lesions may enlarge,

coalesce and fall out giving

a tattered appearance

Sunken brown spots can

form on pods

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Common Bacterial Blight

Initially water-soaked spots

Spots become light brown

lesions of irregular shape

with distinct bright yellow

margins

Lesions enlarge to 10 mm

or larger and kill the leaf

On pods water-soaked

spots enlarge into reddish

brown lesions

Halo Blight

Small water-soaked lesions on the

underside of the leaflet

Develops into numerous small,

reddish-brown lesions

Greenish-yellow halos, highly

variable in size develop around the

spots

Severe infections cause yellowing

and death of new foliage

Pods 1st have small-water soaked

spots and streaks

Water-soaked areas enlarge and

are occasionally surrounded by a

narrow reddish zone

Bacterial Disease Management

Prevention is key!!

Plant only certified, disease-

free seed

Resistant varieties

Some leaves are susceptible

but pods are resistant

Others leaves are resistant

and pods are susceptible

Tillage shortly after harvest

Crop rotation

Onions

Botrytis Leaf Blight

Fungal disease

1st starts as water-soaked

lesions

Lesions develop into whitish in

color from 1-5 mm in length

and surrounded by greenish-

white halos

Center of lesions become

sunken, straw colored

Severely infected plants take

a yellowish cast caused by

coalescing lesions and tip

dieback

Botrytis Leaf Blight – Neck Rot

Appear when in

storage for 2 weeks or

more

Infected scales become

soft, brownish and

spongy

Neck area becomes

sunken and the entire

bulb can become

dried out

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Botrytis Management

Plant certified plant

material

Allow unions to cure

properly before

topping

Remove infected

material in the fall

Purple Blotch

Fungal disease cuased

by Alternaria porri

Small brown spots with

purplish centers on the

leaves

Favorable conditions,

the spots form into

oval lesions that have

purplish tint with

concentric rings

Purple Blotch Management

Sanitation

Plant high-quality

onion seed and

transplants

Bacterial Bulb Rots

Slippery skin

When squeezed the inner rotted

portions slide through the neck

Sour skin

1st appears as tan or brown

partially rotted leaves on the plant

Soft rot develops near the neck and

leaves easily pulled

Diseased scales separate from

healthy ones

Soft rot

Spongy, water-soaked scale

Complete bulb breakdown

Bacterial Bulb Rot Management

Proper curing of onions

before harvesting

Good storage

temperatures and

avoid stacking when

possible

Potato

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Scab

Symptoms are variable

and develop on the

surface of the tuber

Typically – roughly,

circular, raised, tan to

brown, corky lesions of

varying size

Lesion may be raised or

warty in appearance –

level with the surface or

sunken in tuber

Scab Management

Crop rotation

Plant certified potato

seed tubers – Do not save

tubers from garden

Plant resistant when

available

Irrigation – keep the soil

reasonably wet for

several weeks while the

young tubers are

beginning to grow

Bacterial Soft Rot

Rotted tissues that are wet,

cream to tan in color and soft

Rot begins on the tuber surface

and progresses inward

Infected tissue are sharply

delineated from healthy tissue

by dark brown or black

margins

Tissue is usually odorless in the

early stages

Bacterial Soft Rot Management

Use high quality seed

Harvest mature tubers

with well-set skins

Avoid damage to

tubers

Avoid excessive soil

moisture before

harvest

Postharvest curing and

storage temperatures

Fusarium Dry Rot

1st symptoms are dark

depressions on the surface of

the tuber

Large lesions the skin becomes

wrinkled in concentric rings as

the underlying tissue

dessiccates

Necrotic tissue is usually dry

Rotted cavities are lined with

mycelia and spores of various

colors from yellow to white to

pink

Fusarium Dry Rot Management

Plant certified seed

Harvest tubers after

the skins have set and

when their core

temperature is greater

than 50 F

Monitor tubers in

storage often

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Blackheart

Abiotic – oxygen

prevented from

reaching the tuber

center

Internal browning or

blacking of center

tissue

Tissue is firm, not soft

Pattern is irregular

Blackheart Management

Good ventilation in

storage

Avoid poorly drained

ground

Avoid closed bins,

deep piles and poor

ventilation

Avoid temperature

extremes

Hollow Heart

Brown center is

characterized as a

small one-eighth to

one inch diameter

Brown, circular or

elliptic, opaque area

with a diffuse border

Brown center may or

may not develop into

hollow heart

Hollow Heart Management

Plant closer

Use larger, less aged seed

pieces

Establish good plant stands

Avoid plant skips

Apply potassium

Apply nitrogen throughout

season

Schedule irrigation for constant

and uniform tuber growth

Cabbage

Internal Tipburn

Nonpathogenic disorder

Symptoms are death of leaf

tissue, usually along the leaf

margins in the interior of the

head

1st tissue turn tan or light

brown

Eventually it may appear dark

brown or even black

Tissue loses moisture and takes

on a papery appearance

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Cause of Tipburn

Caused by inadequate

supply of available

calcium

Typically it is an

inability to move

calcium in the plant

Drought, water

logging of the soil,

root pruning and other

root symptoms can be

the cause

Sunscald

Missouri Botanical Garden

Missouri Botanical Garden

Small water-soaked

area at the blossom end

Lesion enlarges,

becomes sunken and

turns black and leathery

Secondary pathogens

commonly invade the

lesion

Blossom End Rot

Colorado State University

William Brown Jr.

Cracking

Colorado State University

Michael Bartolo

Catface Get Help If Uncertain About

Your Diagnosis!!!

Plant & Pest Diagnostic Clinic

Rm. 448 Plant Sciences Hall

University of Nebraska

Lincoln, NE 68583-0722

(402) 472-2559

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Department of Plant Pathology

University of Nebraska-Lincoln

Institute of Agriculture and Natural Resources