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G6202, Disease Prevention in Home Vegetable Gardens

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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.

Vegetable Family
Cucumber Cucumber, Watermelon, Squash, Cantaloupe, Pumpkin, Gourds
Cabbage Cabbage, Cauliflower, Brussels sprouts, Broccoli, Mustard, Turnips, Collards
Tomato Tomato, Potato, Pepper (all types), Eggplant
Beet Beets, Spinach, Swiss chard
Bean Beans, Snow peas, Southern peas, English peas
Onion Onions, Shallots, Garlic, Leek
Corn Sweet 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.

Asparagus Cultivar Disease resistance/tolerance
Asparagus Atlas All 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
Beans Cultivar Disease resistance/tolerance
Bush, green
Bush, green bean
Contender Common bean mosaic virus; Powdery mildew
Derby Common bean mosaic virus
Hialeah Common bean mosaic virus
Matador Common bean mosaic virus; Anthracnose
Provider Common bean mosaic virus; Powdery mildew
Tendercrop Common bean mosaic virus; Powdery mildew
Topcrop Common bean mosaic virus
Bush, yellow
Bush, yellow bean
Goldcrop Common bean mosaic virus
Goldkist Rust
Goldmine Common bean mosaic virus; Halo blight
Goldrush Common bean mosaic virus
Beans, Pole Kentucky Wonder Rust
Blue Lake Common bean mosaic virus
Broccoli Cultivar Disease resistance/tolerance
  Arcadia Bacterial soft rot
Brussels sprouts Cultivar Disease resistance/tolerance
  Jade Cross Hybrid Bottom/center rot
Cabbage Cultivar Disease resistance/tolerance
Cabbage Bravo Black rot; Fusarium yellows
Charmant Fusarium yellows
Golden Acre Bacterial spot
Market Prize Black rot; Fusarium yellows
Ruby Perfect Fusarium yellows
Savoy Ace Fusarium yellows
Stonehead Black rot; Fusarium yellows
Cantaloupe Cultivar Disease resistance/tolerance
Cantaloupe Ambrosia Downy mildew; Powdery mildew
Athena Fusarium wilt; Powdery mildew
Eclipse Fusarium wilt; Powdery mildew
Saticoy Fusarium wilt (Race 2); Powdery mildew
Supermarket Fusarium wilt (Race 2); Powdery mildew
Superstar Fusarium wilt (Races 1,2)
Corn, sweet Cultivar Disease resistance/tolerance
Yellow, sugar-enhanced
Sweet corn
Incredible Northern corn leaf blight; Southern corn leaf blight
Legend Stewart's wilt; Smut; Northern corn leaf blight; Southern corn leaf blight
Sugar Ace Stewart's wilt
Tuxedo Stewart's wilt
Bicolor, sugar enhanced Delectable Stewart's wilt
Lancelot Stewart's wilt; Northern corn leaf blight
Seneca Arrowhead Stewart's wilt
Sweet Chorus Stewart's wilt
Sweet Symphony Stewart's wilt; Smut
Temptation Stewart's wilt; Smut
White, sugar enhanced Alpine Stewart's wilt
Seneca Sensation Southern corn leaf blight
Silver King Stewart's wilt; Southern corn leaf blight
Sweet Ice Stewart's wilt; Southern corn leaf blight; Smut
Yellow, supersweet Endeavor Northern corn leaf blight; Southern corn leaf blight
Flagship II Stewart's wilt; Southern corn leaf blight
Morning Star Northern corn leaf blight; Southern corn leaf blight
Saturn Stewart's wilt
Zenith Stewart's wilt; Northern corn leaf blight; Southern corn leaf blight
Bicolor, supersweet Candy Store Stewart's wilt; Smut
Festival Northern corn leaf blight
White, supersweet Ice Queen Stewart's wilt; Northern corn leaf blight; Smut
Summer Sweet 781 Stewart's wilt; Northern corn leaf blight; Southern corn leaf blight
Vail Stewart's wilt; Northern corn leaf blight
Cucumbers Cultivar Disease resistance/tolerance
Slicing
Cucumber
County Fair Bacterial wilt
Dasher II ALS; AN; CMV; Scab; DM; PM
General Lee CMV; Scab; DM; PM
Lightning CMV; Scab; PM
Poinsett 76 ALS; AN; Scab; DM; PM
Speedway ALS; AN; CMV; Scab; DM; PM
Thunder CMV; Scab; PM; ZYM
Pickling Calypso ALS; AN; CMV; Scab; DM; PM
Carolina ALS; AN; CMV; Scab; DM; PM
Francipak M ALS; AN; CMV; Scab; DM; PM
  • ALS = Alternaria leaf spot
  • DM = Downy mildew
  • AN = Anthracnose
  • PM = Powdery mildew
  • CMV = Cucumber mosaic virus
Eggplant Cultivar Disease resistance/tolerance
Eggplant Black Bell Tobacco mosaic virus
Dusky Tobacco mosaic virus
Epic Tobacco mosaic virus
Lettuce Cultivar Disease resistance/tolerance
Lettuce Esmerelda Tipburn
Ithaca Tipburn
Sangria Tipburn
Sierra Tipburn
Summertime Tipburn
Onion Cultivar Disease resistance/tolerance
onion Copra Fusarium wilt
Norstar Botrytis; Mildew; Pinkroot; White mold
Sweet Sandwich Hybrid Pinkroot
Yellow Sweet Spanish Pinkroot
Peas Cultivar Disease resistance/tolerance
Shell peas
Peas
Bolero Bean yellow mosaic virus; Common wilt; Fusarium wilt; Powdery mildew
Green Arrow Fusarium wilt; Downy mildew
Knight Bean yellow mosaic virus; Common wilt; Fusarium wilt; Powdery mildew
Lincoln Common wilt
Little Marvel Fusarium wilt
Spring Fusarium wilt
Snap peas Cascadia Powdery mildew
Oregon Giant Powdery mildew; Common wilt
Sugar Ann Common wilt
Sugar Bon Powdery mildew
Super Snappy Powdery mildew
Super Sugar Pod Powdery mildew
Southern peas Magnolia
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
Pepper Cultivar Disease resistance/tolerance
Hot peppers
Hot pepper
Anaheim TMR 23 Pepper tobamovirus
Caloro PS Pepper tobamovirus
Cherry Bomb Pepper tobamovirus
Delicias Tomato etch virus; Potato virus Y; Pepper mottle virus
Garden Salsa Pepper tobamovirus
Mesilla Tomato etch virus; Potato virus Y; Tabomo
Pasilla Bajio Pepper tobamovirus
Sante Fe Grande Pepper tobamovirus
Senorita Tomato etch virus; Potato virus Y; Pepper mottle virus
Serrano Chili Tomato etch virus; Potato virus Y; Pepper mottle virus
Super CayenneII Tabomo; Bacterial spot (Races 1, 2, 3)
Tam Jalapeno #1 Potato virus Y
Tam Vera Cruz Tomato etch virus; Potato virus Y
Sweet peppers
Sweet pepper
Bell Boy Pepper tobamovirus
Big Bertha PS Pepper tobamovirus
California Doner PS Pepper tobamovirus
California Wonder 300 Pepper tobamovirus
Camelot Bacterial spot (Races 1, 2, 3)
Chocolate Beauty Pepper tobamovirus
Emerald Giant Pepper tobamovirus
Enterprise Bacterial leaf spot; Bacterial spot (Races 1, 2, 3)
Gator Belle Pepper tobamovirus
Golden Summer Pepper tobamovirus
Gypsy Pepper tobamovirus
Jingle Bells Pepper tobamovirus
Jupiter Pepper tobamovirus; Tobacco mosaic virus
Keystone Resistant Giant Tobacco mosaic virus
King Arthur Tobamo; Potato virus Y
Mayata F1RS Pepper tobamovirus
Merlin Pepper tobamovirus
North Star Pepper tobamovirus
Paladin Tobacco mosaic virus; Phytophthora
Peto Wonder Pepper tobamovirus
Pimento Elite Pepper tobamovirus
Rampage Pepper tobamovirus
Red Beauty Pepper tobamovirus
Sentinel Bacterial spot (Races 1, 2); Potato virus Y
Sunsation Tobamo; Bacterial spot (Races 1, 2, 3); Potato virus Y
X3R Aladin Bacterial spot (Races 1, 2, 3); Tobacco mosaic virus
X3R Camelot Bacterial spot (Races 1, 2, 3); Tobacco mosaic virus
X3R Wizard Pepper tobamovirus; Bacterial spot (Races 1, 2, 3); Tobacco mosaic virus
Potato Cultivar Disease resistance/tolerance
Potato, red
Red potato
Chieftan Potato virus A; Scab
Dark Red Norland Leaf roll; Potato virus Y; Potato virus A
La Rouge Scab
Norland Scab
Sangre Early blight
Viking Scab
Potato, russet Belrus Potato virus A; Scab; Leaf roll; Northern root-knot nematode; Potato virus Y; Verticillium wilt
Centennial Early blight; Rhizoctonia; Verticillium wilt; Fusarium dry rot
Frontier Russet Fusarium dry rot
HiLite Russet Scab; Leaf roll; Potato virus X; Potato virus Y
Krantz Scab; Late blight; Verticillium wilt
Lemhi Russet Scab
Norgold Russet Scab
Norkin Russet Scab; Verticillium wilt
Russet Burbank Scab; Blackleg; Leaf roll; Potato virus A
Potato, white
White potato
Allegany Early blight; Late blight; Verticilium wilt
Atlantic Scab; Potato virus X; Verticillium wilt; Pink eye
Gemchip Verticillium wilt
Irish Cobble Potato virus A; Wart
Katahdin Potato virus A; Southern bacterial wilt
Kenebec Black leg; Late blight; Potato virus A; Potato virus Y
Monona Potato virus A; Scab; Potato virus Y; Verticillium wilt
Norchip Scab
Norwis Leaf roll; Potato virus X; Potato virus Y
Onaway Potato virus A; Scab; Late blight
Sebago Potato virus A; Early blight; Potato virus X; Potato virus Y; Late blight; Wart; Southern bacterial wilt
Superior Scab
Potato, yellow Yukon Gold Potato virus A; Leaf roll
Pumpkin Cultivar Disease resistance/tolerance
Pumpkin Howden Black rot
Jack O Lantern Black rot
Magic Lantern Powdery mildew
Merlin Powdery mildew
Spinach Cultivar Disease resistance/tolerance
Spinach Decatur Downy mildew
Melody Downy mildew; Cucumber mosaic virus
Polka Downy mildew
Tyee Downy mildew; Cucumber mosaic virus;
Unipak Downy mildew
Squash Cultivar Disease resistance/tolerance
Zucchini
Zucchini squash
Dividend Cucumber mosaic virus; Watermelon mosaic virus; Zucchini yellow mosaic virus;
Independence II Watermelon mosaic virus; Zucchini yellow mosaic virus
Revenue Cucumber mosaic virus; Watermelon mosaic virus; Zucchini yellow mosaic virus
Spineless Beauty Powdery mildew
Yellow straightneck Gen. Patton Powdery mildew
Liberator III Cucumber mosaic virus; Watermelon mosaic virus; Zucchini yellow mosaic virus
Multipik Cucumber mosaic virus; Watermelon mosaic virus
Yellow crookneck Prelude II Watermelon mosaic virus; Powdery mildew
Patty pan types Sunburst Cucumber mosaic virus; Watermelon mosaic virus
Winter acorn Taybelle PM Powdery mildew
Sweet potato Cultivar Disease resistance/tolerance
Sweet potato Beauregard Soil rot; Internal cork
Centennial Root-knot; Internal cork
Jewel Root-knot; Fusarium; Internal cork
Tomato Cultivar Disease resistance/tolerance
Tomato Beef Master VT; F1; N; AS; M
Better Boy VT; F1; N; AS
Big Beef F12; GL; N; TM; VT; AS; EB
Carnival F12; GL; N; TM; VT; AS
Celebrity F12; GL; N; TM; VT; AS;
Floralina F12; GL; VT
Florida 47 F12; VT
Jet Star F1; VT
Mt. Delight F12; VT; BE
Mt. Fresh F12; VT; BE; EB
Mt. Gold F12; VT;
Mt. Pride F12; VT; AS;
Mt. Spring F12; VT; BE;
Mt. Supreme F12; VT; EB
Pink Girl F12; GL; VT; AS;
Spitfire F12; 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
Watermelon Cultivar Disease resistance/tolerance
Seeded
Watermelon
Carnival Anthracnose; Fusarium wilt (Race 1)
Crimson Sweet Anthracnose; Fusarium wilt (Race 1)
Fiesta Anthracnose; Fusarium wilt (Race 1)
Mardi Gras Anthracnose; Fusarium wilt (Race 1)
Regency Fusarium wilt (Race 1)
Royal Sweet Fusarium wilt (Race 1)
Sangria Anthracnose; Fusarium wilt (Race 1)
Star Brite Anthracnose; Fusarium wilt (Race 1)
Stars n' Stripes Anthracnose; Fusarium wilt (Race 1)
Tiger Baby Fusarium wilt (Race 1)
Verona Anthracnose; Fusarium wilt (Race 1)
Seedless Constitution Fusarium wilt (Race 1)
Freedom Fusarium wilt (Race 1)
Revolution Fusarium wilt (Race 1)
SummerSweet 5244 Anthracnose
SummerSweet 5544 Fusarium wilt (Race 1)
Tri-X 313 Anthracnose; Fusarium wilt (Race 1)

G6202 Disease Prevention in Home Vegetable Gardens | University of Missouri Extension