Tomatoes are probably the most popular vegetable grown by gardeners. The majority of the problems in growing them are environmental and are generally not infectious to other crops you might have planted. Choosing the right plant is just as important as location in controlling some common issues. Look for a cultivar that is disease resistant, especially to verticillium wilt, fusarium races 1 2, nematodes, and tobacco mosaic virus. Using good general sanitation practices by keeping weeds and rotten or fallen fruit away from the plants, and washing your hands and tools after handling or working with plants, are the best ways to not spread any disease present.
Problems can be categorized into several groups: insects, physiological (culture or environment), fungus, bacterial or viral.
Common Insects: Tomato and tobacco hornworms, whiteflies, aphids, stink bugs, and cutworms. Southern gardeners are bothered by corn earworms and potato beetles. Methods of control for these pests vary.
For hornworms, hand-picking is the best solution because several of the species of Sphinx moths (the tomato hornworm is the larvae) are pollinators of endangered native orchids. You can also make netting covers if hornworms are a problem. For larger plots and if you need an environmental control use, Bacillus thuringensis. This the same control agent for cutworms.
For whitefly and aphids, using an Insecticidal Soap should be an effective control. The damage from whitefly is usually minimal; they’re mostly a nuisance when they fly up in your face!
Stink bugs cause damage visible on green fruit, appearing as dark pinprick spots that remain green or yellow as the fruit ripens. Keep the growing area and surrounding area free of weeds since the bugs overwinter in these areas.
For earworms and beetles the same controls are recommended: insecticidal soaps and Bacillus thuringensis.
Physiological Problems: Blossom drop, blossom end rot, leaf roll, sunscald, fruit crack, numerous trace mineral deficiencies, and over-fertilization with high nitrogen. Overwatering and underwatering, and sudden cold spells are common causes.
Blossom drop is the most susceptible to dry soils and cold spells but could also be caused by heavy rains, too much nitrogen or a bacterial or fungal infection. Blossom end rot is usually associated with extremes in soil moisture. This can also lead to calcium deficiencies.
Fruit crack happens with rapid growth during rainy spells followed by dry periods. During dry periods water plants and apply mulch.
Sunscald happens when green tomatoes are exposed to direct sunshine for long periods. Allowing the plant to develop some suckers provides a canopy of leaves to protect the new fruit.
If your plant has sprouted lots of bright green leaves but very few blossoms or fruit, cease fertilizing with a high nitrogen fertilizer and use one with a higher P and K number, the second and third number.
Fungal Diseases: Most can be treated with Bordeaux Mixture, Copper Soap or Sulfur Dust. The best control is to plant resistant-strain cultivars. Before treating determine which fungal infection your plants are infected with (anthracnose, botrysis fruit rot, damping off, fusarium wilt, gray leaf spot, early or late blight, septoria leaf spot, or soil rot fungus). As with all diseased plant material, its best to not compost any diseased material and to clean all tools.
Bacterial spot causes small lesions on leaves that turn black. Green fruit will develop black, raised spots that will become pitted. There is no effective treatment for bacterial spot and it’s best to remove and destroy the plant and to wash all tools to keep the infection from spreading.