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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.)
