Tomato plants are planted in most vegetable gardens but are susceptible to a wide range of problems. Insects, improper care and disease can threaten the health of tomato plants and cause them to suddenly wilt. This can happen at any time during the growing season, and gardeners must know when to remove the plant or when to try to save it. If the problem is caused by disease, tomato plants should be removed from the garden so the disease cannot spread to others.
Tomatoes have extensive root systems that extend 36 inches or more from the plant. They need a steady supply of moisture to produce healthy foliage and fruit. If there is not enough moisture available naturally in the soil or from supplemental watering, the plant wilts. But if there's too much water, the oxygen supply to the roots system is cut off, also resulting in wilting. If a wilted plant sits in water-logged soil for more than two days, it is usually attacked by fungal diseases such as root rot and dies.
Fusarium wilt is more likely to occur in warmer climates. It shows up as the yellowing and then browning of the older leaves and main stem. When the main stem of an affected plant is split open, the middle is dark brown instead of green. Because fusarium wilt affects the plant's vascular system, through which water is carried from the base of the plant, the plant wilts and dies.
Nematodes are microscopic worms that invade the root systems of certain plants, including tomatoes. Once they enter the root systems, they reproduce and form a series of "knots"--galls or swollen areas along the root system that are easily visible when the plant is pulled from the ground. Water and nutrients cannot get past the obstructions and scar tissue caused by the nematodes, and the plant wilts.
Too Much High Nitrogen Fertilizer
An often overlooked reason for tomato plants wilting is too much high nitrogen fertilizer applied at the beginning of the season. Nitrogen encourages top growth of tomato plants at the expense of root formation. Once hot summer weather begins, the root system is insufficient to transport the water needed to keep the top green growth alive, and the plant wilts.
Verticillium wilt occurs later in the season and is caused by a fungus that enters the roots after the soil is waterlogged for several days. Although verticillium wilt and fusarium wilt have the same symptoms of browning leaves and wilting foliage, verticillium wilt causes the plant's stem to turn brown up to 12 inches from the soil while fusarium wilt causes the entire stem to discolor.