The leaves of my tomato plant are being eaten by something. Some of the stems are completely bare of leaves. Is there anything I can do to protect my plants?
— Steve Goldman, Skokie
I suspect you have a tomato hornworm or tobacco hornworm caterpillar that is eating your tomato. Small tomato hornworms are yellow to white in color with no markings. These caterpillars can reach 4 inches long. They turn green with white bars and have a
slender horn pointed upward at the rear end. They can be difficult to find, as their color blends in with tomato foliage. They can consume a large amount of foliage in a short time and will also feed on fruits. It’s not unusual for gardeners to miss seeing them until considerable damage has been done. Another sign of hornworm feeding is the accumulation of their large, black droppings on leaves and the ground. In addition to tomatoes (which are their favorite plants to feed on), hornworms may also feed on eggplant, potatoes and peppers.
Tobacco hornworm caterpillars are usually green with seven diagonal white lines on their sides and have a curved red horn. They develop into the Carolina sphinx moth. Tomato hornworm caterpillars have eight V-shaped marks on each side, and their horns are straighter and blue-black in color. They develop into the five-spotted hawkmoth.
All you need to do is to hand-pick the caterpillar(s) off of your tomato plant for control. There is no need to spray tomatoes for hornworm caterpillars — just check your tomatoes a couple of times a week and remove any caterpillars. There is a parasitic wasp that attacks the caterpillar by placing its eggs under the skin of the hornworm. When the wasp larvae hatch, they feed on the hornworm caterpillar and pupate. The pupae are small white cocoons that look like grains of rice on the back of the hornworm. The hornworm caterpillars will then stop feeding and become a source for increasing the wasp population, so do not remove them. We like to call this nature’s free pest control!
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.