Disease Prevention in Home Vegetable Gardens

Patricia Donald
Department of Plant Microbiology and Pathology
Lewis Jett
Department of Horticulture

Vegetable gardening is the number one hobby in the United States. Keeping a garden healthy and attractive requires attention not only to its size and location but also to the soil, water availability, sunlight and air circulation in the garden. These environmental conditions can determine susceptibility to plant diseases. Diseased plants are unsightly and also detract from the enjoyment and fruits of the hobby.

Diseases affect home garden vegetable plants every year. Plant pathogens become established when environmental conditions are favorable. Losses due to disease can be reduced through a combination of proven disease-prevention methods:

  • Select adapted, disease-resistant varieties.
  • Use transplants that are free from disease.
  • Plant closely related vegetables in separate areas of the garden (Table 1).
  • Rotate garden areas to prevent planting closely related vegetables in the same area year after year.
  • Control weeds that compete with vegetables or harbor plant pathogens.
  • Control insects that may carry disease.
  • Remove and destroy diseased plant material.
  • Remove plant refuse soon after harvest.
  • Disinfect garden tools and shears.
  • Apply fungicides appropriately and in a timely manner when resistant varieties are not available.
  • Maintain a balanced soil fertility program.

In addition to diseases caused by pathogens, many nonparasitic disorders cause serious problems in vegetable production. The following disorders may mimic symptoms caused by pathogens: extremes in temperature, extremes in moisture, extremes in one or more nutrients, and herbicide misapplication or carryover. These disorders will not respond to the use of chemicals aimed at plant pathogens and can make conditions more favorable for disease development.

Table 1
Vegetable families susceptible to similar diseases.

VegetableFamily
CucumberCucumber, Watermelon, Squash, Cantaloupe, Pumpkin, Gourds
CabbageCabbage, Cauliflower, Brussels sprouts, Broccoli, Mustard, Turnips, Collards
TomatoTomato, Potato, Pepper (all types), Eggplant
BeetBeets, Spinach, Swiss chard
BeanBeans, Snow peas, Southern peas, English peas
OnionOnions, Shallots, Garlic, Leek
CornSweet corn

Getting started

Sanitation
Many plant pathogens survive through the winter in old plants and plant debris remaining in the garden. Removal of the plant material will reduce the chance of certain diseases increasing over years. It also reduces the chance that healthy plants will become infested early in the season. Some plant diseases would naturally occur late in the season and not be a problem on older plants. These same diseases can be devastating on young plants if pathogens are present early in the season.

Debris from diseased plants should not be added to a compost pile, because the temperatures reached in the pile often are not sufficient to kill the pathogens. Burying the plant debris outside the garden will reduce the chance of spreading a disease from debris to plants currently in the garden or to plants that will be in the garden the next year. Some pathogens such as the wilt fungi survive in the soil for many years, and prevention is the best way to manage these diseases.

In addition to removing plant material from the garden, it is important to remove, destroy or disinfest support structures such as wooden stakes and poles used in the garden.

Garden tools can be disinfested by washing them with detergent. Washing will remove soil and adhering fungi or bacteria, and the detergent will remove some of the virus from the tools and inactivate any remaining virus.

Clean seeds and transplants help reduce the chance of introducing plant pathogens into the garden. Do not save seed if disease is present in the garden. Whether growing your own transplants or purchasing them, transplants should be carefully inspected for abnormal growth above and below ground. Reject multipaks of transplants if several cells do not have plants or contain dead plants. Inspect transplants for insect damage on the leaf surface or insects on the lower leaf surface. If growing your own transplants, purchase steam-sterilized growth medium. Disinfest flats with bleach or use new plastic containers.

Certain plant pathogens can grow on weeds and spread to garden plants. For example, aster yellows phytoplasma can be spread from dandilions to carrots by the aster leafhopper. Additionally, some weeds attract insects that transmit diseases. This is especially true of viral diseases.

Cultural practices
The garden site should be well drained. Waterlogged soil encourages development of root rotting fungi, whereas good drainage promotes good growth of plant roots and thus the entire plant. If soil drainage is marginal, building a raised bed may solve the drainage problems.

Plants with the proper available nutrients can withstand environmental stresses and plant pathogen attacks better than plants growing in soil with low fertility or where there is a nutrient imbalance.

Plant-parasitic nematodes, especially root-knot, can be a problem in the garden.

Crop rotation is a good way to manage diseases that attack related plants such as tomatoes, potatoes and eggplants (Table 1). Moving the location of the related plants within the garden from season to season lessens the chance that plant diseases will build up. This is especially true of pathogens which survive in the soil. A good rule of thumb is to avoid returning to the same area of the garden for at least three years. This will not prevent diseases with long-lived resting spores, such as Pythium, Fusarium and Rhizoctonia.

Plant at the recommended seeding rate to reduce competition between plants and promote good air circulation and sunlight penetration. Use viable seed with good germination potential. Use seed packaged for the current year. The seed packet should have a date on it.

Physical practices
Plastic sheeting and organic mulch provide a physical barrier between soil and plant surfaces and reduce the amount of disease inoculum splashed onto foliage, stems and fruits during rainy periods.

Staking and trellising
To reduce the incidence of fruit rot in the garden, keep the fruit as far away from the soil as possible. Staking or trellising are especially effective with tomatoes. Sunburn can also be avoided if plants are grown in such a way that the leaves shade the fruit.

Solarization
Soil solarization is a nonchemical way to rid the garden of soil-borne plant pathogens. Solarization uses energy from the sun to heat the soil causing physical, chemical and biological changes in the soil. The process is most effective in mid to late summer, when high air temperatures combine with high radiation from the sun. The elevated temperature and toxic products generated from solarization kill or suppress plant pathogens and weed seed. It is believed that beneficial organisms are harmed less by solarization than by fumigation. Solarization also stimulates release of nutrients from organic matter present in the soil.

The biggest disadvantage to this method is that the area treated must be out of production for most of the growing season. Soil to be solarized should be tilled so that the soil is as uniform as possible (free of clods and plant debris) to prevent pockets of untreated soil. Slight elevation of the treated area will minimize recontamination of treated soil. A raised center of the bed will facilitate rainfall shedding. Water sitting on the plastic reduces the effectiveness of the treatment.

Check soil fertility and, if necessary, add fertilizer before beginning solarization. Dry soil should be moistened to a level that is ideal for planting. Wet soil conducts heat better than dry soil and will allow the heat to move deeper in the soil to remove pathogens present in the root zone.

Use clear plastic (1 to 6 mils) to cover the soil. Thinner plastic allows better solarization. The plastic needs to be stretched tight over the soil surface and be in contact with the soil. It is important to bury the edges of the plastic to prevent easy removal of the plastic before the soil has been adequately treated. Soil temperatures need to be over 100 F for four to six weeks to reduce soil-borne pathogens.

Contaminated plants introduced into the treated soil will undo the effects of solarization. Also mixing of adjacent soil with the treated soil will dilute the benefits of solarization.

Biological practices
Resistant varieties provide one of the best ways to manage plant disease in the garden (Table 2). Resistance to a disease means that the plant is less likely to show symptoms than susceptible varieties; it does not mean that the plant is immune to that disease. Resistance to one disease does not protect against other diseases. Use of resistant varieties if available is especially recommended when a disease is known to occur in your area. Seed packets and catalogs are good sources of information about disease-resistant varieties. Be sure to check that the variety with disease resistance is adapted to your area before ordering seed.

After planting

Sanitation
Make a practice of removing diseased plants or plant parts from the garden without delay. It is often more cost-effective to remove plants than to try to bring them back to health. Removal also helps reduce the chance that disease will spread. Look for leaf spots, wilts, stunting, fruit rots, malformed leaves, and cankers. Bury diseased plant material away from the garden; do not place it in a compost pile.

Many plant pathogens require moisture to survive and infect plants. Avoid working in the garden when foliage is wet, because this can spread plant pathogens.

During the growing season

Good cultural practices
The following practices will help maintain healthy plants during the growing season:

  • Maintain adequate levels of plant nutrients without overfertilizing. Excess nitrogen application can promote some root-rotting fungi. Nutrient stress can make plants more susceptible to diseases and insect damage.
  • Water when the plants are dry to avoid drought stress. Excess water can lead to plant death from lack of oxygen to the roots or because of pathogen attack.
  • Maintain adequate mulch cover to conserve moisture and reduce weed growth. Certain nonparasitic diseases such as blossom end rot can occur when moisture levels to the roots are uneven.
  • Harvest produce at peak maturity. Overripe vegetables will attract insects and other pests.
  • Remove nonbearing and old plants immediately after harvest to prevent accumulation of plant debris in the garden area.

Chemical control
Sometimes resistant varieties are not available and disease occurs in the garden despite all the cultural practices used. Many leaf diseases can be managed by spraying or dusting plants with an effective fungicide. Most fungicides are protectants. They work on the plant surface and protect against infection. They do not eliminate established infections. If disease is not detected early, the plant may die and disease may spread despite fungicide treatment. Some fungicides are systemic and will move in the plant. Some of these have curative properties and will kill infections already established in the plant, but they will not remove the spots already present on the leaves.

Table 2
Vegetables with resistance or tolerance to important diseases and nematode pests.

AsparagusCultivarDisease resistance/tolerance
AsparagusAtlasAll cultivars possess rust resistance. All except Mary Washington possess Fusarium wilt resistance.
Greenwich
Jersey Knight
Jersey Gem
Jersey King
Jersey Prince
Mary Washington
UC 157 F2
BeansCultivarDisease resistance/tolerance
Bush, green
Bush, green bean
ContenderCommon bean mosaic virus; Powdery mildew
DerbyCommon bean mosaic virus
HialeahCommon bean mosaic virus
MatadorCommon bean mosaic virus; Anthracnose
ProviderCommon bean mosaic virus; Powdery mildew
TendercropCommon bean mosaic virus; Powdery mildew
TopcropCommon bean mosaic virus
Bush, yellow
Bush, yellow bean
GoldcropCommon bean mosaic virus
GoldkistRust
GoldmineCommon bean mosaic virus; Halo blight
GoldrushCommon bean mosaic virus
Beans, PoleKentucky WonderRust
Blue LakeCommon bean mosaic virus
BroccoliCultivarDisease resistance/tolerance
 ArcadiaBacterial soft rot
Brussels sproutsCultivarDisease resistance/tolerance
 Jade Cross HybridBottom/center rot
CabbageCultivarDisease resistance/tolerance
CabbageBravoBlack rot; Fusarium yellows
CharmantFusarium yellows
Golden AcreBacterial spot
Market PrizeBlack rot; Fusarium yellows
Ruby PerfectFusarium yellows
Savoy AceFusarium yellows
StoneheadBlack rot; Fusarium yellows
CantaloupeCultivarDisease resistance/tolerance
CantaloupeAmbrosiaDowny mildew; Powdery mildew
AthenaFusarium wilt; Powdery mildew
EclipseFusarium wilt; Powdery mildew
SaticoyFusarium wilt (Race 2); Powdery mildew
SupermarketFusarium wilt (Race 2); Powdery mildew
SuperstarFusarium wilt (Races 1,2)
Corn, sweetCultivarDisease resistance/tolerance
Yellow, sugar-enhanced
Sweet corn
IncredibleNorthern corn leaf blight; Southern corn leaf blight
LegendStewart's wilt; Smut; Northern corn leaf blight; Southern corn leaf blight
Sugar AceStewart's wilt
TuxedoStewart's wilt
Bicolor, sugar enhancedDelectableStewart's wilt
LancelotStewart's wilt; Northern corn leaf blight
Seneca ArrowheadStewart's wilt
Sweet ChorusStewart's wilt
Sweet SymphonyStewart's wilt; Smut
TemptationStewart's wilt; Smut
White, sugar enhancedAlpineStewart's wilt
Seneca SensationSouthern corn leaf blight
Silver KingStewart's wilt; Southern corn leaf blight
Sweet IceStewart's wilt; Southern corn leaf blight; Smut
Yellow, supersweetEndeavorNorthern corn leaf blight; Southern corn leaf blight
Flagship IIStewart's wilt; Southern corn leaf blight
Morning StarNorthern corn leaf blight; Southern corn leaf blight
SaturnStewart's wilt
ZenithStewart's wilt; Northern corn leaf blight; Southern corn leaf blight
Bicolor, supersweetCandy StoreStewart's wilt; Smut
FestivalNorthern corn leaf blight
White, supersweetIce QueenStewart's wilt; Northern corn leaf blight; Smut
Summer Sweet 781Stewart's wilt; Northern corn leaf blight; Southern corn leaf blight
VailStewart's wilt; Northern corn leaf blight
CucumbersCultivarDisease resistance/tolerance
Slicing
Cucumber
County FairBacterial wilt
Dasher IIALS; AN; CMV; Scab; DM; PM
General LeeCMV; Scab; DM; PM
LightningCMV; Scab; PM
Poinsett 76ALS; AN; Scab; DM; PM
SpeedwayALS; AN; CMV; Scab; DM; PM
ThunderCMV; Scab; PM; ZYM
PicklingCalypsoALS; AN; CMV; Scab; DM; PM
CarolinaALS; AN; CMV; Scab; DM; PM
Francipak MALS; AN; CMV; Scab; DM; PM
  • ALS = Alternaria leaf spot
  • DM = Downy mildew
  • AN = Anthracnose
  • PM = Powdery mildew
  • CMV = Cucumber mosaic virus
EggplantCultivarDisease resistance/tolerance
EggplantBlack BellTobacco mosaic virus
DuskyTobacco mosaic virus
EpicTobacco mosaic virus
LettuceCultivarDisease resistance/tolerance
LettuceEsmereldaTipburn
IthacaTipburn
SangriaTipburn
SierraTipburn
SummertimeTipburn
OnionCultivarDisease resistance/tolerance
onionCopraFusarium wilt
NorstarBotrytis; Mildew; Pinkroot; White mold
Sweet Sandwich HybridPinkroot
Yellow Sweet SpanishPinkroot
PeasCultivarDisease resistance/tolerance
Shell peas
Peas
BoleroBean yellow mosaic virus; Common wilt; Fusarium wilt; Powdery mildew
Green ArrowFusarium wilt; Downy mildew
KnightBean yellow mosaic virus; Common wilt; Fusarium wilt; Powdery mildew
LincolnCommon wilt
Little MarvelFusarium wilt
SpringFusarium wilt
Snap peasCascadiaPowdery mildew
Oregon GiantPowdery mildew; Common wilt
Sugar AnnCommon wilt
Sugar BonPowdery mildew
Super SnappyPowdery mildew
Super Sugar PodPowdery mildew
Southern peasMagnolia
Mississippi Pinkeye
Mississippi Purple
Mississippi Silver
Pinkeye Purple Hull BVR (different resistance)
Tolerance to blackeye cowpea mosaic virus and related viruses.Resistance to root-knot nematodes and Fusarium wilt
PepperCultivarDisease resistance/tolerance
Hot peppers
Hot pepper
Anaheim TMR 23Pepper tobamovirus
Caloro PSPepper tobamovirus
Cherry BombPepper tobamovirus
DeliciasTomato etch virus; Potato virus Y; Pepper mottle virus
Garden SalsaPepper tobamovirus
MesillaTomato etch virus; Potato virus Y; Tabomo
Pasilla BajioPepper tobamovirus
Sante Fe GrandePepper tobamovirus
SenoritaTomato etch virus; Potato virus Y; Pepper mottle virus
Serrano ChiliTomato etch virus; Potato virus Y; Pepper mottle virus
Super CayenneIITabomo; Bacterial spot (Races 1, 2, 3)
Tam Jalapeno #1Potato virus Y
Tam Vera CruzTomato etch virus; Potato virus Y
Sweet peppers
Sweet pepper
Bell BoyPepper tobamovirus
Big Bertha PSPepper tobamovirus
California Doner PSPepper tobamovirus
California Wonder 300Pepper tobamovirus
CamelotBacterial spot (Races 1, 2, 3)
Chocolate BeautyPepper tobamovirus
Emerald GiantPepper tobamovirus
EnterpriseBacterial leaf spot; Bacterial spot (Races 1, 2, 3)
Gator BellePepper tobamovirus
Golden SummerPepper tobamovirus
GypsyPepper tobamovirus
Jingle BellsPepper tobamovirus
JupiterPepper tobamovirus; Tobacco mosaic virus
Keystone Resistant GiantTobacco mosaic virus
King ArthurTobamo; Potato virus Y
Mayata F1RSPepper tobamovirus
MerlinPepper tobamovirus
North StarPepper tobamovirus
PaladinTobacco mosaic virus; Phytophthora
Peto WonderPepper tobamovirus
Pimento ElitePepper tobamovirus
RampagePepper tobamovirus
Red BeautyPepper tobamovirus
SentinelBacterial spot (Races 1, 2); Potato virus Y
SunsationTobamo; Bacterial spot (Races 1, 2, 3); Potato virus Y
X3R AladinBacterial spot (Races 1, 2, 3); Tobacco mosaic virus
X3R CamelotBacterial spot (Races 1, 2, 3); Tobacco mosaic virus
X3R WizardPepper tobamovirus; Bacterial spot (Races 1, 2, 3); Tobacco mosaic virus
PotatoCultivarDisease resistance/tolerance
Potato, red
Red potato
ChieftanPotato virus A; Scab
Dark Red NorlandLeaf roll; Potato virus Y; Potato virus A
La RougeScab
NorlandScab
SangreEarly blight
VikingScab
Potato, russetBelrusPotato virus A; Scab; Leaf roll; Northern root-knot nematode; Potato virus Y; Verticillium wilt
CentennialEarly blight; Rhizoctonia; Verticillium wilt; Fusarium dry rot
Frontier RussetFusarium dry rot
HiLite RussetScab; Leaf roll; Potato virus X; Potato virus Y
KrantzScab; Late blight; Verticillium wilt
Lemhi RussetScab
Norgold RussetScab
Norkin RussetScab; Verticillium wilt
Russet BurbankScab; Blackleg; Leaf roll; Potato virus A
Potato, white
White potato
AlleganyEarly blight; Late blight; Verticilium wilt
AtlanticScab; Potato virus X; Verticillium wilt; Pink eye
GemchipVerticillium wilt
Irish CobblePotato virus A; Wart
KatahdinPotato virus A; Southern bacterial wilt
KenebecBlack leg; Late blight; Potato virus A; Potato virus Y
MononaPotato virus A; Scab; Potato virus Y; Verticillium wilt
NorchipScab
NorwisLeaf roll; Potato virus X; Potato virus Y
OnawayPotato virus A; Scab; Late blight
SebagoPotato virus A; Early blight; Potato virus X; Potato virus Y; Late blight; Wart; Southern bacterial wilt
SuperiorScab
Potato, yellowYukon GoldPotato virus A; Leaf roll
PumpkinCultivarDisease resistance/tolerance
PumpkinHowdenBlack rot
Jack O LanternBlack rot
Magic LanternPowdery mildew
MerlinPowdery mildew
SpinachCultivarDisease resistance/tolerance
SpinachDecaturDowny mildew
MelodyDowny mildew; Cucumber mosaic virus
PolkaDowny mildew
TyeeDowny mildew; Cucumber mosaic virus;
UnipakDowny mildew
SquashCultivarDisease resistance/tolerance
Zucchini
Zucchini squash
DividendCucumber mosaic virus; Watermelon mosaic virus; Zucchini yellow mosaic virus;
Independence IIWatermelon mosaic virus; Zucchini yellow mosaic virus
RevenueCucumber mosaic virus; Watermelon mosaic virus; Zucchini yellow mosaic virus
Spineless BeautyPowdery mildew
Yellow straightneckGen. PattonPowdery mildew
Liberator IIICucumber mosaic virus; Watermelon mosaic virus; Zucchini yellow mosaic virus
MultipikCucumber mosaic virus; Watermelon mosaic virus
Yellow crookneckPrelude IIWatermelon mosaic virus; Powdery mildew
Patty pan typesSunburstCucumber mosaic virus; Watermelon mosaic virus
Winter acornTaybelle PMPowdery mildew
Sweet potatoCultivarDisease resistance/tolerance
Sweet potatoBeauregardSoil rot; Internal cork
CentennialRoot-knot; Internal cork
JewelRoot-knot; Fusarium; Internal cork
TomatoCultivarDisease resistance/tolerance
TomatoBeef MasterVT; F1; N; AS; M
Better BoyVT; F1; N; AS
Big BeefF12; GL; N; TM; VT; AS; EB
CarnivalF12; GL; N; TM; VT; AS
CelebrityF12; GL; N; TM; VT; AS;
FloralinaF12; GL; VT
Florida 47F12; VT
Jet StarF1; VT
Mt. DelightF12; VT; BE
Mt. FreshF12; VT; BE; EB
Mt. GoldF12; VT;
Mt. PrideF12; VT; AS;
Mt. SpringF12; VT; BE;
Mt. SupremeF12; VT; EB
Pink GirlF12; GL; VT; AS;
SpitfireF12; GL; VT; EB
  • AS = Alternaria stem canker
  • GL = Gray leaf spot
  • BE = Blossom end rot
  • N = Root-knot nematode
  • EB = Early blight
  • TM = Tobacco mosaic
  • F12 = Fusarium wilt races 1,2
  • VT = Verticillium wilt
WatermelonCultivarDisease resistance/tolerance
Seeded
Watermelon
CarnivalAnthracnose; Fusarium wilt (Race 1)
Crimson SweetAnthracnose; Fusarium wilt (Race 1)
FiestaAnthracnose; Fusarium wilt (Race 1)
Mardi GrasAnthracnose; Fusarium wilt (Race 1)
RegencyFusarium wilt (Race 1)
Royal SweetFusarium wilt (Race 1)
SangriaAnthracnose; Fusarium wilt (Race 1)
Star BriteAnthracnose; Fusarium wilt (Race 1)
Stars n' StripesAnthracnose; Fusarium wilt (Race 1)
Tiger BabyFusarium wilt (Race 1)
VeronaAnthracnose; Fusarium wilt (Race 1)
SeedlessConstitutionFusarium wilt (Race 1)
FreedomFusarium wilt (Race 1)
RevolutionFusarium wilt (Race 1)
SummerSweet 5244Anthracnose
SummerSweet 5544Fusarium wilt (Race 1)
Tri-X 313Anthracnose; Fusarium wilt (Race 1)