Tomato plants are easy to grow, but they are susceptible to numerous pests and diseases. Gardeners can maintain healthy plants by providing adequate irrigation and monitoring for pests. Leave sufficient room between tomato plants to allow good air circulation when they reach maturity. Apply dry or water-soluble fertilizer for tomato plants at the rate and schedule recommended by the manufacturer. Remove and destroy insect-damaged or diseased fruit, leaves and stems, and keep the area around plants free from weeds and debris.
Hornworms grow about 4 inches long, and are green with horn-shaped extensions on their hind parts. They are the larvae of hummingbird moths, also called hawk or sphinx moths. Hornworms are voracious eaters and can quickly defoliate an entire tomato plant. They stay on the inside foliage of plants during the hot part of the day and move to the outer leaves when the temperature cools down. You can remove hornworms by hand, use bacillus thuringensis (BT), a biological control, or apply a chemical pesticide approved for hornworms on tomato plants. Apply BT or chemical pesticides according to the manufacturer's directions.
Tomato fruitworms are the larvae of a light yellow- to olive-colored moth. Young worms are yellowish white with brown heads. As they mature, they change colors to greenish, yellow, brown or black with pale stripes. They grow up to 1 ½ inches long.
Tomato fruitworms eat the leaves and fruits of tomato plants. They can be controlled with BT or Neem oil applied at the rate recommended by the manufacturer.
Tomato pinworms are a serious threat to tomato plants. The worms grow to ¼ inch long and are yellow-gray or green with purple spots. They roll and tie the tips of leaves together, and tunnel into foliage and fruit. The best method of control is to apply a chemical insecticide approved for tomato pinworms on plants, and follow manufacturer's instructions.
Flea beetles are tiny jumping insects that chew small holes in the leaves of tomato plants. Seedlings and transplants are subject to the most damage. If the infestation is severe, affected plants can lose vigor and even die. Use repellants, such as diatomaceous earth, horticultural oil or Neem oil on tomato plants to deter flea beetles. Apply according to the manufacturer's directions. Chemical insecticides are ineffective because flea beetles move quickly from one plant to another.
Psyllids are small insects that lay orange or yellow eggs on the undersides of the foliage on tomato plants. The nymphs are greenish-yellow flat discs about 1/4-inch in size when they hatch. They do not move, but constantly feed on the leaves. Affected foliage turns yellow along the mid-veins and leaf edges. New growth is narrow and small, and stands upright. Psyllids are difficult to control, and the plants often decline and die.