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

fungusviruses

Common plant pathogens and

their size relative to each other and to a plant

cell

VirusesTo small to been seen with a light microscopePlants are stunted, chlorotic, and may not produce seedTransmitted by aphids, mites, beetles, other insects, nematodes and fungi

Tomato spotted wilt virusKansas State Research and Extension

Squash Mosaic Virus

BacteriaSingle-celled organismsAn opening is required for infection to occur1st seen is a water soaked spots that will turn necrotic

FungiMost fungi require free moisture to infect the plantDoes not need openings in the plant to cause infectionLargest group of pathogens that we manage

Nematodes

Microscopic worm-like animalsFeed on roots and above ground partsRoots become distorted, bottle brushed or galled after feeding

Disease System Componentsenvironment

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

Cucurbits

Bacterial Wilt

Dull green patches appear on damaged leavesEntire leaves and petioles wilt and progress to entire plantFruit 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

LeavesLight, water-soaked or pale green spotsSpots to enlarge to angular gray-to-white spotsTissue in the spots tears easily

FruitGray, slightly sunken spotsGummy plant sap may exudeSpots become darker with age

Scab of Cucurbits

T.A. Zitter

Use disease-free seedGrow plants in warm locations with good air and soil drainageAvoid overhead irrigation

Scab - Management

Tomatoes

Small, brownish lesions initially forms on foliageYellow halo surrounding lesionLesion enlarges rapidly to form concentric ringsFruit 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 leavesDark brown margin with a gray or tan centerSpots may coalesceTiny black specks present in mature spots

Anthracnose

Small, circular indented spot in the skin on fruit beginning to ripenEnlarge to ½ inch and becomes sunkenCenter becomes dark in coloration or concentric rings of dark specks develop

Early Blight, Septoria and Anthracnose - Management

Pathogen-free seed/transplantsResistant cultivarsGood air circulationRemove infected tissue and fruitAvoid overhead watering, otherwise water in the morningMaintain a balanced soil fertility

Late Blight

Cornell UniversityKent 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

Dispose of infected plants/fruits – Do not make cull pilesDestroy volunteer tomatoes and potatoesScout regularly for early detectionFungicide sprays at label rates and intervals

Late Blight - Management

Bacterial Spot

Symptoms on leaves and stemsCircular to irregular shape up to 1/8 inchSimilar to septoria leaf spot – no grayish brown centerYellow halo surrounds spots

Bacterial Spot

Symptoms on fruitGreen fruit susceptibleInitially starts as water-soaked spotEnlarge to 1/8-1/4 inchGray-grown in coloration Scabby with sunken pitted centers

Bacterial Speck

FoliarSmall 1/16-1/4 inch black spotsSlightly raisedYellow halo

FruitYoung, green fruitSlight raised 1/32-1/16 inch diameter spotSuperficial

Bacterial Disease Management

Good sanitation in the fall and during the growing seasonRotate position of tomatoes in garden – avoid planting pepper in the same area as tomatoAvoid overcrowdingWater at the base of the plants –soaker hoses when possiblePurchase 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

Virus Infected TomatoTomato Bushy Stunt Virus Tomato Spotted Wilt Virus

Cloudy SpotTomato

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 increasesInitial symptoms are indefinite tan lesionsAs lesions grows, concentric black rings may form

Anthracnose - Management

Planting pathogen-free seed/transplantSanitation – remove infected fruitPick fruit frequently

Bacterial Leaf Spot

Necrotic spots on leaves, stems and fruit1st starts as water soaked areas on underside of leavesEnlarge to ¼ inch, turn dark brown and slightly raised (lower side)Upper surface – depress with a brown border around a beige centerLeaves yellow and dropFruit spots are raised and scablike

Bacterial Leaf Spot - Management

Plant disease free seed and transplantsCrop rotation for at least 1 year rotation between tomato or pepper

Sunscald

Missouri Botanical Garden

Missouri Botanical Garden

Small water-soaked area at the blossom endLesion enlarges, becomes sunken and turns black and leatherySecondary pathogens commonly invade the lesion

Blossom End Rot

Colorado State UniversityWilliam Brown Jr.

Cracking

Colorado State UniversityMichael Bartolo

Catface

Apples

Foliar symptomsFruit

symptoms

Severe Defoliation (Aug-Sep)

Apple Scab

Inoculum for next year

Black lesions on both sides of leaf, severe infection may yellow leafScabby spots on fruitResistant varieties (Some resistant to cedar-apple rust also)

Majority of the common apple varieties are susceptible

i.e. Golden Delicious, Granny Smith, JonathanPrune annually to open canopyRake and remove any leaves in fallFungicide applications

Apple Scab

Cedar-Apple Rust

Upper leaf surface

Lower leaf surface

Aecial spores

Telial spores

Yellow, orange lesions on leaf surface and long tendrils on leaf underside

Yellow, orange lesions on fruit often near the blossom end

Cedar-Apple Rust

Plant a resistant varietyApples, crabapples, junipers, etc

Controlling disease on junipers

Fungicide costly – July-SeptRemove gallsEradication of nearby junipers – effectiveness debatable

Fungicide application in April and June

Management of Cedar-Apple Rust

Light brown to blackened leavesBlack “shepherd’s crook”Water-soaked blossomsDried fruitBacterial ooze from infected branches

Fire Blight – Apple and Pear

West Virginia University

Washington State UniversityT.J. Smith

Fire Blight – Life Cycle

Resistant varieties

Prune out infected branches

Best during winter monthsPrune 8 to 12 inches below the edge of visible infectionSterilize pruning tools after each cut

Fire Blight - Management

Fire Blight – Variety SusceptibilityDegree of Susceptibility

Host Extreme Moderate Resistant

Apple BraeburnFujiGalaJohnathan

Early McIntoshGranny SmithGolden DeliciousJonagold

Red DeliciousWinesapPriscilla

Pear AuroraBartlettMax-Red Bartlett

AnjouDawnSparklett

Harrow DelightMoonglowStarking Delicious(Maxine)

Crabapple Prairie FireRed JadeSnowdriftStrathmore

BrandywineHopaRed SplendorSnow Cloud

CoralburstIndian SummerRadiantRed Vein RussianVanguard

Peaches

Leaves have small round, tan to purplish spotsCenter drops out giving a “Shothole” appearanceSmall, slightly sunken red spots on fruitClear, gummy exudate on fruitRough, smoky-appearing cankers develop on 2 to 4 year old wood

Shothole

Oregon State University

Avoid sprinkler irrigation water to wet tree foliage and fruitRemove affected twigsFungicide applications

Spray at 50% leaf fall in late autumnSpray again during the dormant seasonSpray again at shuck fall in the spring

Shothole - Management

Blossoms quickly turn brown or black and dieSmall tufts of dusty brown to gray fungal growth presentSmall, elliptical cankers with gum productionFruit develops light brown spots that enlarge rapidly.Completely rotted fruit within a day or twoRotted fruit shrivels to form a “mummy”

Brown Rot of Stone Fruits

J.W. Travis

Brown Rot - Management

SanitationRemove all rotted fruit and mummies

Prune out twig cankersRemove wild plum thickets that are adjacent to orchardsSeveral fungicide applications

Flower infections – apply at pink, bloom and petal fallFruit – start about 1 month before harvest

Oregon State University

Strawberries

StemsLesions 1st appear as small, dark spotsEnlarge to become dark, elongated, dry sunken lesionsGirdling common

FruitsWhitish, water soaked lesionsTurn a light tan to dark brownEventually become sunken and blackPink to orange spore mass develops

Anthracnose

University of Florida

Plant disease-free plantsMinimize overhead irrigationMulching with straw instead of plasticRemove infected plant partsFungicide use

Once established in planting, it is difficult to control with fungicides

Anthracnose - Management

Lesion begin as small, firm, light brown spots

Lesion enlarge quickly

Fruit becomes covered with gray to brown spores

Gray Mold - Berries

APS Press

University of Florida

Select a site with good air circulationCanopy pruning to increase air movement (raspberry)Avoid crowding plantsStraw mulch to form barrier between fruit and soil (strawberry)Soaker hose wateringRemove plant debris as for leaf diseasesFungicide applications at 7 - 10 day intervals during bloom

Gray Mold - ManagementUniversity of Florida

pdc.unl.edu

Get Help If Uncertain About Your Diagnosis!!!

Plant & Pest Diagnostic ClinicRm. 448 Plant Sciences Hall

University of NebraskaLincoln, NE 68583-0722

(402) 472-2559

Department of Plant PathologyUniversity of Nebraska-Lincoln

Institute of Agriculture and Natural Resources