Volume XXIX Number 1 Page 7

By Brad Haire
University of Georgia

Diseases can turn the dream of a bountiful garden crop into a nightmare come harvest time. But gardeners can do a few things to reduce the risk these veggie enemies pose.

"Most vegetables are susceptible to a number of diseases," said David Langston, a vegetable plant pathologist with the University of Georgia College of Agricultural and Environmental Sciences.

Wilts, leaf spots, blights and fruit rots, he said, are just a few of the problems that plague vegetable gardens every year. Plant diseases are caused by four main types of organisms: fungi, bacteria, nematodes and viruses.

Attack time

When conditions are wet and temperatures warm, vegetable plants are more susceptible to diseases caused by fungi and bacteria. Scout your garden regularly.

When 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 Service 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, because you can't distinguish healthy seeds from diseased seeds. Make sure you follow directions on when and how to plant them.

Best defense

Disease-resistant plant varieties are the most efficient way of controlling vegetable diseases. Buy resistant varieties when you can. Resistance traits are usually listed in seed catalogs and in plant stores.

Don'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-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.

Veggie cousins

Vegetable families include:

• Alliaceae (chives, garlic, leeks and onions).
• Brassicaceae (broccoli, Brussels sprouts, cabbage, cauliflower, collards, mustard, radishes, rutabagas and turnips).
• Cucurbitaceae (cantaloupes, cucumbers, honeydew melons, pumpkins, squash and watermelons).
• Fabaceae (all beans, English peas and Southern peas).
• Solanaceae (eggplant, peppers, potatoes and tomatoes).
• Asteraceae (lettuce).
• Poaceae (corn).
• Malvaceae (okra).
• Chenopodiaceae (spinach)
• Apiaceae (carrots).

"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.

Be careful

When you water the garden, don't splash soil onto plant foliage. If possible, irrigate by running water between the rows. Use a mulch layer of straw, bark, shredded paper or plastic to keep soil from splashing onto plants and keep fruit 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.)