Published on 03/18/98

What Happened to My Tomatoes?

Even when you seem to have done everything right, tomatoes can fail in the garden. Here are a few of the reasons why.

Failure to set fruit. The causes: cool night air and soil (below 55 degrees), abnormally hot weather, low soil moisture, too much shade or overfertilizing. For early tomatoes, use varieties that will set well during the cold of April.

Blossom end rot. This disorder causes the fruit to have a dark, sunken area on the blossom end. You can prevent it by maintaining even soil moisture. Other causes: root damage limiting the uptake and movement of calcium. Mulches help moderate soil moisture fluctuations as well as eliminate the need for cultivation. Improper pH can keep the plant from absorbing enough calcium, too.

Mosaic diseases. Several viruses will produce mottling and curling of leaves and disfiguration of tomatoes. Insects (often aphids), animals and people spread these diseases. Don't let anyone smoke in your garden. If you smoke, always wash your hands before touching the plants. Tobacco mosaic virus from an infected cigarette can be spread to tomatoes as well as to cucumbers, squashes, asters, roses and many other plants.

Wilt. Both Fusarium and Verticillium can cause tomatoes to die early. They cause the plant to wilt even with good moisture. If you cut the stem, the vascular tissue will be discolored. Both wilts are soil-borne and widespread in the South. The only solution is to use resistant varieties.

Leaf Roll. With this disorder, older leaves roll upward. Symptoms usually are seen when plants have a heavy fruit load. Environmental factors reported to promote symptoms include high heat, drought and prolonged times of wet soil.

Blights and Other Fungal Diseases. A number of fungi are important on tomatoes. Most can be controlled by regular sprays of recommended fungicides. For early and late blights, anthracnose and fruit rots, use a fungicide once each week when the disease first appears.

Herbicide Injury. Hormone-type herbicides such as 2,4-D or Banvel D used near the garden can cause serious damage on tomatoes. The symptoms are downward-curling leaves and twisting new growth. Don't spray these products on a windy day or near the garden. Don't use grass clippings for a mulch or in a compost pile, either, if the lawn was recently treated with a herbicide.

Aphids. These can cause a loss of plant vigor and may carry disease. Many chemical products will control aphids. Read and follow label directions. Insecticidal soap is an organic spray that controls many soft-bodied insects, too.

Whitefly. Whitefly has become a major problem in tomatoes. Many times touching a plant will send up a cloud of white. They feed on the plant, causing weak growth.

Tomato Hornworm. This large green worm has a horn on the back end. Hand-pick these large insects from small plantings. Bacillus thuringiensis (Bt) can be used as a biological control for hornworms when they're small.

Root knot. Affected plants usually are stunted and may wilt in hot, dry weather. An easy-to-see symptom: the roots contain elongated and round swellings (root knots). Nematodes — tiny, usually microscopic worms — are the cause. Rotate crops and buy resistant transplants (the letter N will follow the variety name) from a reputable nursery.

Wayne McLaurin is a professor emeritus of horticulture with the University of Georgia College of Agricultural and Environmental Sciences.