Tomato plants are generally easy to grow but they can be attacked by a variety of fungal, bacterial, viral, and other diseases. Since the symptoms are similar in these numerous afflictions, you need to identify the specific disease that may be attacking your plants before you can treat it effectively.
Tomato plants are subject to numerous rots and cankers caused by molds. Fungal diseases ordinarily thrive in humid weather and wet soil that is not well drained. Fungal diseases include Alternaria stem canker, Early blight, Damping off, Fusarium crown and root rot, Fusarium wilt, Gray leaf spot, Gray mold, Leaf mold, Powdery mildew, Septoria leaf spot, Southern blight, White mold, Target spot, and Verticillium wilt.
The symptoms of fungal disease include a range of spots on the leaves and tomatoes, cankers on the stems, plus root and crown rot.
Bacterial diseases include Canker, Speck, Spot, and Pitch necrosis. These diseases can cause brown, mealy pith in the stem, stunted leaves, dark brown and black spots with yellow halos on the tomatoes, elongated or streaky spots on leaves, and rotting stems.
Stunted plants and yellow leaves can be caused by numerous viral diseases including Alfalfa mosaic, Cucumber mosaic, Curly top, Potato leafroll, Potato virus Y, Pseudo curly top, Tobacco etch, Tobacco mosaic, Tobacco mosaic and Potato virus X, and Tomato yellow leaf curl.
Water molds, Oomycota, thrive in running water and high humidity. Oomycota, means egg fungi, but water molds are not true fungus. They are responsible for Damping Off, Buckeye Rot and Late blight.
Buying Seeds and Seedlings
Hybrid tomato plants have been developed to resist certain diseases. These usually are labeled with a code indicating the disease they resist. They include Verticillium wilt (V), Fusarium wilt (F),Southern root-knot nematode (N) Early blight (A), and Tomato mosaic virus (T). A label listing VFAT means that it resists Verticillium wilt, Fusarium wilt, Early blight, and Tomato mosaic virus.
Make sure your tomatoes get plenty of sun; water them on the ground, not with sprinklers. Space your plants wide enough to let them get air, and don't handle them when they are wet.
Plant tomatoes in the same place only once every three to four years, and keep them free of weeds. Use organic or plastic mulch to avoid blossom end rot. If you spot a diseased plant, remove it immediately then clean your tools.
Keep tobacco away from your plants; tobacco can carry the damaging Tobacco mosaic virus that can kill tomato plants.
To treat a disease, you first have to identify it. The diseases affecting your tomato depend on the weather in your area, the variety of tomato, and the kind of soil. Many diseases show similar symptoms, so you need to look at photos. To find qualify photographs of diseases that affect tomatoes, Google “Vegetable MD online, Cornell University.” Follow the interior links showing tomato plants suffering from various plant diseases.
Some diseases that attack tomato plants can be treated with fungicides and other chemicals. Others cannot. If your tomato plants have Late blight, a serious disease, Google, "Late blight tomato, EPA approved treatments." Cornell University’s plant clinic will usually be at the top of Google’s list of sites. Other universities also give dependable recommendations; these include Oregon State University, the University of California, Davis, Purdue University, the University of Florida, and Texas A & M University.