By Brad Haire
University of Georgia
Plant diseases are caused by four main types of organisms: fungi, bacteria, nematodes and viruses.
Vegetable plants are more susceptible to diseases caused by fungi and bacteria when conditions are wet and warm. Scout your garden regularly.
What to look forWhen the garden is dry, nematode damage is more evident. You can test your soil for nematodes by submitting a sample through your county UGA Extension office.
Viral diseases can show up at any time, Langston said.
Many plant diseases can be on or within the seeds. "Seeds should not be saved from year to year," he said. "This is important to prevent a number of diseases."
Buy seeds from a reputable dealer. You can't distinguish healthy seeds from diseased seeds. Make sure you follow directions on when and how to plant them.
Planting disease-resistant varieties are best way to control vegetable diseases. Buy resistant varieties when you can. Resistance traits are usually listed in seed catalogs and in plant stores.
Lots of sunDon't plant your garden near or beneath trees. The shade will reduce the drying of plant foliage after rain and increase the chances of diseases. Besides, vegetables like a lot of sunlight, and the trees will compete for vital nutrients.
Crop rotation is important. If you keep planting the same vegetables in the same spot year after year, you're asking for soil-borne disease problems.
Grow the same or closely related vegetable plants in the same soil only once every three to five years, Langston said. This practice starves out most pathogens that cause stem and leaf diseases.
What to rotateVegetable families include:
- Alliaceae (chives, garlic, leeks and onions).
- Apiaceae (carrots).
- Asteraceae (lettuce).
- Brassicaceae (broccoli, Brussels sprouts, cabbage, cauliflower, collards, mustard, radishes, rutabagas and turnips).
- Chenopodiaceae (spinach).
- Cucurbitaceae (cantaloupes, cucumbers, honeydew melons, pumpkins, squash and watermelons).
- Fabaceae (all beans, English peas and Southern peas).
- Malvaceae (okra).
- Poaceae (corn).
- Solanaceae (eggplant, peppers, potatoes and tomatoes).
More tips"Trap crops" can reduce viral diseases carried by small insects. Plant a few rows of a crop like rye or corn around your main garden. This will tempt insects to feed there first, reducing the risk of diseases some small insects are known to carry.
When you water the garden, don't splash soil onto plant foliage. If possible, run the water between the rows. Use a mulch layer of straw, bark, shredded paper or plastic to keep the soil from splashing onto plants and keep fruits from touching bare ground.
If you use tobacco, wash your hands thoroughly before handling plants. This will prevent the spread of tobacco mosaic virus, which can infect many kinds of vegetables, particularly tomatoes and peppers.
After harvest, remove and destroy all plants from the garden and sanitize your garden equipment. This will reduce the overwintering of disease-causing organisms.
Most important, use proper cultural practices to keep your plants healthy. "Healthy plants don't get diseases as easily as weak ones," Langston said. "Healthy plants are the best control against plant diseases."
(Brad Haire is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.)