Tomatoes, grown in fields, gardens, containers and greenhouses, are susceptible to attack from a number of diseases, rodents and insect pests throughout their life cycle. While you don't have to stand guard over your plants, careful observation and regular monitoring allows you to recognize the onset of insect attacks before damage gets out of hand and destroys your prized tomato crop.
The tomato fruitworm and tobacco budworm are larvae of moths that are able to feed on the poisonous foliage of the tomato plants without harm. The fruitworm is commonly found in colder climates, while the budworm prefers warmer locations. Similar in appearance, these caterpillars have brown heads and yellow-to-white bodies that change to shades of pale green to reddish-brown, with stripes that run the length of their body as they grow. Both worms feed on the leaves, buds and fruits, and are more active at dusk than in the daytime. The worms lay eggs on the foliage of the tomato plant. Parasitic wasps and certain insecticides, such as Asana, Guthion and Lannate can be used to eradicate these pests.
Tomato pinworms are found in warmer climates and also in greenhouses in colder climates. They feed on the leaves, stems and fruits, causing minimal damage in early stages, and greater damage as they age and are able to web leaves together and bore into stems. Young larvae are just a few millimeters in length and yellow to gray in color. Older caterpillars turn spotted in shades of yellow, green and purple. Tomato pinworm infestations can be controlled by insecticide or with pheromone traps that disrupt mating cycles.
Vegetable leafminers are maggots that lack color at hatching and turn bright yellow with black mouths when fully grown. They live and breed year round in southern climates and can survive winter in the soil in colder areas. As their name suggests, leafminers create S-shaped mines through tomato foliage which then leaves the plant susceptible to bacterial and fungal diseases. The damage created by the leafminer also reduces the tomato plants' ability to photosynthesize and causes the leaves to turn brown. Removal of infected foliage and insecticides are the best methods of controlling the leafminer population.
Aphids are miniscule, pear-shaped, winged and wingless insects that feed on the foliage and stems of tomato plants, sucking large amounts of sap from the plant. In addition to the draining effect, they excrete honeydew that provides the optimal conditions for sooty mold growths. Aphids can also transport diseases from one plant to the next. Ranging in size from 1/16 to 1/8 inch, these pests feed in colonies, and like to hang on stems and beneath leaves. The most effective method of aphid control is through insecticidal soap or neem oil applications. Natural predators like parasitic wasps, ants and lacewings can also help control the aphid population.
Hornworms are daunting green worms with a horn on the back end and seven to eight V-shaped markings along each side. Hornworms, larvae of the sphinx moth, can grow up to 4 inches in length. They feed on the foliage and completely strip leaves from the plant, while infrequently feeding on the fruit, leaving superficial scars. Picking worms off by hand, use of insecticides such as carbaryl and permethrin, and parasitic wasps are effective methods of controlling hornworms in the garden. Soil should be tilled to kill off remaining pupae, after the growing season is complete.
There are several types of whiteflies, including silverleaf, greenhouse and iris, that can cause tremendous damage to tomato plants. Measuring under 2mm in length, whiteflies feed in groups and usually reside on the underside of foliage. Whiteflies drain plants of essential sap, cause foliage to brown and fall off, and excrete honeydew which creates optimal breeding grounds for diseases like sooty black mold. Insecticides are the least effective method of dealing with whiteflies, therefore a combination of vacuuming, hosing plants and removal of infected leaves is the best way to control and eliminate whitefly populations. Natural predators, such as lacewings and lady beetles can also aid in controlling infestations.