Wilts, leaf spots, blights and fruit rots are just a few of the problems that plague vegetable gardens every year. Plant diseases are caused by four primary types of organisms: fungi, bacteria, nematodes and viruses.
When conditions are wet and temperatures warm, your vegetable plants are more susceptible to disease caused by fungi and bacteria.
Scout your garden regularly so you can stay on top of these things. Sometimes all you have to do is pick off a leaf or two to help prevent problems from spreading.
When garden conditions are dry, nematode damage can be more evident. Soil can be sampled for nematodes by submitting a sample through your Extension office.
Virus diseases can occur at any time.
Many plant diseases can be on or within the seed. This is why seed should not be saved from year to year unless you have an heirloom variety. This is important to prevent a number of diseases. Buying seed in packets ensure that you are buying western grown seed, which means the plants were grown in arid conditions.
Disease resistant plant varieties are the most efficient way of controlling vegetable diseases, so buy resistant varieties when you can. Resistance traits are usually listed in seed catalogs and on labels on transplants.
Don’t plant your garden near or beneath trees if you can avoid it. The shade will reduce the drying of plant foliage after rain and increase the chances of diseases. Besides, vegetables like a lot of sunlight (at least 6-8 hours a day), and the trees will compete for vital nutrients.
Crop rotation is important. If you continue to plant the same vegetables in the same spot year after year, you are asking for soil disease problems. This can be challenging for those with limited garden space, but you should still try to do this if possible.
In an ideal situation, you should grow the same or closely related vegetable plants in the same soil only once every three to five years. This practice starves out most pathogens that cause stem and leaf diseases.
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)
• Malvaceae (okra)
• Chenopodiaceae (spinach)
• Apiaceae (carrots)
Trap crops and companion plants can reduce virus diseases carried by small insects. Plant a few rows like rye (in spring and fall gardens) or corn around your main garden. Or plant different flowers – anything that blooms. This will tempt insects to feed there first, reducing the risk of diseases some small insects are known to carry.
If you water overhead (with a sprinkler) water early in the morning and not during late afternoon or evening. Watering early in the morning allows the foliage on the plants to dry quicker. Also when watering, try to avoid splashing soil onto plant foliage. If possible, irrigate by running water between the rows. Use a mulch layer of pine or wheat straw, bark, shredded paper or plastic to keep soil from splashing onto plants or 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.
Keep weeds to a minimum. Weeds compete with the vegetables for nutrients, water light and growing space. Certain ones can also attract insects that carry diseases.
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.