Tomatoes are one of the most popular plants to grow, but they are suspect to problems and disease. Addressing diseases at the first sign of symptoms is important for the health of the infected plant and the healthy plants in your garden. One of these symptoms on tomato plants is yellow leaves. Yellow leaves can indicate several problems.
The location of yellow leaves on your tomato plant helps you identify the problem. Yellow leaves at the bottom of the plant that have brown spots indicate early blight, a fungal infection that can spread to uninfected plants and other members of the nightshade family (potatoes, eggplant and others). If the plant is yellowing from the top down and the leaves are curling, the plant may be infected with curly top virus. Depending on the pattern of yellowing, the plant could also be infected with Fusarium or Verticillium wilt. Nematodes attacking tomato roots can also cause yellow leaves. Pests like spider mites will yellow tomato leaves. Online resources like Cornell University's Vegetable MD Online can help you identify the problem.
Whatever the source of yellowing tomato leaves, fruit production will be significantly reduced, or the entire plant can die if left untreated. There is no effective treatment for problems like curly top virus. Removing the plant from your garden is your only option for protecting healthy plants. Plants infected with early blight can be treated, but reduced foliage can result in discolored tomato fruit, known as sun scar.
Yellow leaves on tomato plants can occur any time during the growing season. Diagnosing the problem as soon as possible is essential to treating infected plants. Several antifungal treatments are effective for early blight. Contact your county garden extension office to find out the most effective treatment in your area. Diseases like curly top virus and Fusarium wilt kill tomato plants quickly.
Many hybrid tomato plants are resistant to Fusarium wilt and nematodes, denoted by an "F" and "N" on the plant label. Purchase resistant plant varieties whenever possible. Early blight can be treated with several different fungicides. Organic remedies are also available. Spider mite infestations are treated with malathion or sulfur dust. To prevent fungal infections like early blight, make sure there is plenty of ventilation around tomato plants and avoid watering from the top of the plant. Plastic mulch around the base of the plant can prevent fungal spores from splashing onto leaves in wet conditions.
Choosing resistant varieties of tomato plants, treating disease symptoms quickly, and removing untreatable plants help preserve your garden. Healthy plants with adequate sunlight, drainage, ventilation and nutrients resist infestation better than weak or neglected plants. Supplement tomato plants with fertilizer throughout the growing season to keep them healthy.