Tomato plants are easy to grow, but they are subject to attack by numerous insects. Some insects cause minimal damage, while others can cause loss of fruit, and even the death of the plant. Check tomato plants daily for signs of insect damage. If the infestation is minor, remove and destroy the affected plant parts. If the infestation is severe, use insecticidal soap according to the manufacturer's directions. Chemical pesticides should be used as a last resort, and should be applied following the manufacturer's instructions.
Worms damage the foliage and fruit of tomato plants by chewing or boring holes. Tomato pinworms bore dry shallow pinholes into stalks, buds and green fruit. Later, the pinholes on the fruit develop into discolored blotches. Tomato fruitworms also bore holes into the stalks, buds and green fruit, which then decay.
Hornworms can strip all the leaves from a tomato plant in a few hours. If there is no foliage for them to eat, they will feed on green fruits and leave large shallow scars.
At night, cutworms chew through the stems of tomato plants at ground level, causing the plant to fall over. They hide in the soil at the base of the plants during the day. Cabbage loopers eat the tissue between the veins of the leaves on tomato plants. They rarely cause serious damage, although the fruit may experience sunscald due to lack of protective foliage.
Blister beetles chew ragged holes on the edge of the leaves on tomato plants, but cause minimal damage. Colorado potato beetles feed on the foliage and the terminal growth, which can result in lower yields or even the death of affected plants. Flea beetles chew small, circular holes in the leaves. If the infestation is severe, small plants can die as a result of the lost foliage.
Aphids suck the sap from the leaves and fruit of tomato plants, causing discoloration and mottling. Whiteflies also suck the foliage, which results in yellow leaves, premature leaf drop and stunted growth. Both spread viral diseases from plant to plant. Sooty mold is a fungus that grows on the honeydew excreted by aphids and whiteflies.
Stinkbugs and thrips pierce the flower buds on tomato plants to suck the sap, causing the blossoms to fall off or to produce deformed fruit. Thrips also suck the sap from the leaf buds and leaves, which causes the foliage to appear silvery or bronzed.