Do you know what diseases to look for on your tomatoes? Keep your tomato crop in top shape by avoiding some common diseases:
Early blight:
"Early blight affects the tomato foliage, the fruits and the stems. It is caused by the Alternaria solani fungus. Symptoms include dark spots that have concentric rings. A bulls-eye pattern may develop. The oldest leaves develop this first, and the leaves may fade to yellow. If the leaves die the tomatoes are left exposed and may be subject to sun scald.
Cure: The affected tomato plants must be removed and all debris must be disposed of. This fungus is soil borne, and will survive the winter. Therefore anything an affected tomato plant has touched should be removed as it is most likely contaminated. You should use a resistant tomato cultivar and rotate your crops.
Late blight:
Late blight is caused by the Phytophthora infestans fungus and affects both tomatoes and potatoes. It is especially dangerous if the weather is particularly cool and wet. Late blight was the fungus that caused the Irish Potato famine. The leaves will have lesions and will appear as irregular gray spots. If the weather is damp a white mold may appear around the spots. Once the tomato fruits become infected they will develop dark regions that will cover a large percentage of the tomato. The fungus may be spread tomato plant to tomato plant by wind or rain.
Cure: Make sure you allow adequate spacing between the tomato plants and avoid overhead watering especially in the afternoon or evening. Pull out and destroy any effected tomato plants. Make sure you don't use any rotten potatoes in your compost as this is a carrier of the fungus.
Bacterial Wilt:
Bacterial wilt is caused by Ralstonia solanacearum, which enters the tomato plants roots through wounds made by insects, or natural wounds that occur where secondary roots begin to grow. The disease grows most easily in a warm and moist environment. Once inside the tomato plant the bacteria multiplies quickly and fills the plant with slime. This leads to the wilting of the plant, but the leaves remain green.
Cure: Bacterial wilt is very hard to control as the bacteria can survive in the soil for several seasons. Make sure you remove any infected tomato plants and the soil the tomatoes touched if possible. Crop rotation has been known to help, especially with plants that aren't affected by the bacteria such as beans, cabbage, and corn.
Southern Blight:
Southern Blight is caused by the Sclerotium rolfsii fungus. Generally the first symptom is the drooping of the tomato leaves, which is common for other wilts. Next a brownish dry rot will develop on the tomato plant right near the soil line. Next a white fungus will begin to develop and lesions will develop on the stems. This will in turn cause the whole tomato plant to wilt and die.
Cure: Unfortunately the fungus can live for years in the soil, so if your crop develops this destroy the tomato plants and any soil the tomato plants touched. In addition crop rotation with plants that aren't affected by the fungus could help, as you never know if you really removed all the contaminated soil."