Tomato plants may just be the quintessential vegetable garden plant. They are easy to maintain, come in several different varieties, and can be grown just about anywhere--indoors or out. However, while tomato plants are flexible, they are susceptible to a number of diseases. While proper care is the best preventative measure, repeatedly infected tomato plants should be placed with resistant cultivars.
Tomato plants affected with bacterial spot develop small circular or irregular lesions often surrounded by a yellow halo. The lesions most often appear on leaf tips or edges but can affect tomato stems, flowers and fruit. As the disease progresses, the spots grow in size and leaves with many spots turn yellow and eventually drop. Prune affected plant tissue then spray with copper fungicide to control the spread of the disease.
Bacterial speck creates small dark lesions on the leaves and fruit of tomato plants. On leaves, the specks are very small (no larger than 2 mm) and surrounded by a yellow halo. If the black specks are numerous, they can distort the leaf and cause it to brown at the edges. Only immature tomatoes, smaller than 3 cm in diameter develop bacterial specks often surrounded by a narrow green or yellow halo. These specks can easily be scraped off. Prune affected plant tissue, then spray with copper fungicide to control the spread of the disease.
Bacterial canker has a wide variety of symptoms and not all plants will develop all of the symptoms. The bottom leaves of the tomato plant wilt first and the disease spreads upward. Often times, only one side of the plant or the leaf will wilt. As the disease progresses, the leaves brown and a yellow band separates dead and live plant tissue. The tomato plant's stems may develop lighter streaks that later darken and break open to form cankers. In severe infections, a yellow fluid may ooze from cuts in the stem when it is squeezed. Tomato fruit develops small (3 to 6mm) lesions with light brown centers and greasy white halos. Bacterial canker is highly contagious and difficult to control. There are no chemical treatments prescribed for bacterial canker. Uproot affected plants, sterilize the soil (or choose another spot) and replace them with tomato plants that are certified as canker-free.
Tomato plants suffer from early blight and late blight. Tomato plants affected with early blight have leaves with large banded or bulls-eyed black patches surrounded by a yellow halo. Tomato plants affected with late blight have leaves marred by what looks like large water-logged areas that eventually turn brown and thin. Their fruit will develop large green-brown patches with a greasy appearance. Green or black patches may also develop on the stems. Both diseases can be managed with pruning and fungicide sprays prescribed to treat early or late blight.
Spotted wilt is a virus that causes tomato leaves to develop yellow speckling and dark streaks. The tips of the leaves may also turn brown and die. Tomatoes suffering from spotted wilt become malformed and feature raised yellow red and green lesions. There is no cure for the virus. To prevent future crops from being affected, control the thrip population that harbors the disease and plant a more resistant variety of tomato plant.
Tomato plants infected with verticillium wilt have leaves that wilt at the edges. As the disease progresses, the leaves eventually turn yellow and then brown and the tomato plant's growth becomes stunted. The best cure for verticillium wilt is to uproot infected plants and replace them with a wilt-resistant variety.