I saw your recent column about tomato fruitworms, and was wondering if this pest also eats leaves. The leaves of one of my tomato plants are being eaten by something. A couple of the branches now have no leaves. I am wondering what is going on with my tomato and am worried about the other plants.
— Sam Gilbert, Glenview
I suspect you have a tomato hornworm or tobacco hornworm caterpillar eating your tomato foliage. This is not a big concern in my opinion, as only one of your tomato plants shows damage. The tomato fruitworm feeds on fruit, not leaves. Small tomato hornworms are yellow to white with no markings and are very difficult to see. These caterpillars can reach 4 inches long and are green with white bars and a slender horn pointed upward at the rear end, making them difficult to find, as their color blends in with tomato foliage. They can consume a large amount of foliage in a short period of time and also feed on fruits, working from the outside in. It’s not unusual for gardeners to miss seeing them until considerable damage has happened. 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 generally green with diagonal yellowish-white lines on their sides and have a curved red horn. They develop into the Carolina sphinx moth. Tomato hornworm caterpillars have V-shaped white marks on each side, and their horns are straighter and blue-black in color. They develop into the five-spotted hawkmoth.
Hand-pick these caterpillars off your tomato plants and relocate them to your garden for control. There is no need to spray tomatoes for hornworm caterpillars; check your tomatoes a couple of times a week and remove any caterpillars. The adults are good pollinators, so leave a caterpillar or two on your tomatoes to complete their life cycle, provided no significant damage is being done. I personally think the caterpillars are very cool-looking due to their color and size. There is a parasitic wasp that attacks them by placing its eggs under the skin of the hornworm. When the wasp larvae hatch, they will feed internally and pupate. The pupae are small white cocoons that look like grains of rice on the back of the hornworm. The hornworm caterpillars will stop feeding and will be a source for increasing the wasp population, so do not remove them.
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.
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