Tomato plants need warm weather and plenty of sun. Two types of tomato plants are available to the home gardener. Determinate varieties grow smaller and growth stops when the fruit has set on the first bud. Indeterminate varieties grow larger and need to be supported by a cage or trellis or be tied to stakes. These do not stop growing until after first frost.
Early blight, which is caused by a fungus, appears in the early spring and is one of the most common diseases of tomato plant leaves. It begins at the bottom of the plant and makes the bottom leaves turn brown. The disease not only spreads to the top of the plant, but can spread to other plants, as well. If it is caught early and the bottom leaves picked off before the disease spreads, the progression can be stopped. Without the leaves to protect them from the sun, the tomatoes will develop a condition known as sun scald. The speed at which the disease spreads depends on the temperature. At lower temperatures, it will take about two hours for the spores to germinate. When the temperature rises to between 80 and 85 F, it only takes a half-hour. Spreading mulch around the plants will limit the development of the fungal spores.
Tomato Spotted Wilt Virus
Tomato spotted wilt virus is one of the most serious of the tomato plant diseases, often causing the death of the plant. The leaves will become distorted, wilted and turn a pale green. Many times they will develop purplish gray spots. Younger leaves will turn bronze and develop small dark spots. The stems will develop brown/purple streaks. Ripe fruit will develop yellow splotches and rings. The growth of the plant will become stunted. Two insects, aphids and thrips, are responsible for spreading the virus to other plants. There is no cure for the virus. The only thing to do is to remove and destroy any infected plants and try to control the insects.
Bacterial wilt is another fatal disease of tomato plants. It acts so fast that the plant will die without showing any external symptoms. It only takes two to three days for the whole plant to become infected. The only way to tell is to peel away the bark just above the soil line. The disease will be present if the interior looks waterlogged. In the more advanced stages of the disease, the center of the stem will be brown and hollow. In some instances, the disease will progress at a slower rate where the plant becomes stunted and roots sprout from the stem, however the results will be the same. The plant has to be destroyed.
Bacterial canker will cause the plant to wilt, starting with the lowest leaves, which will turn yellow, curl, wilt, turn brown, shrivel up and collapse. It works its way up the plant, with white spots eventually appearing on the tomatoes and the leaves turning black. In some cases, it will affect only one side of the leaf. If the stems are affected, they will become streaked with brown or yellow and the center will be yellow or reddish brown. Bacterial canker can also attack the fruit, appearing as yellow or brown raised spots that are encircled by a while halo. Bacterial canker will not survive in the soil. Turn the infected plants under at the end of the season; it will decompose and the canker will die. It can take as long as 10 months for it to completely die, so to be on the safe side, plant a different vegetable in that spot the next year.