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Tomato Hornworms

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Tomato hornworm Manduca quinquemaculata

Tomato Hornworm. Photo courtesy of Katie Hobson http://www.gardenpunks.com

Katie Hobson

Name:

Tomato Hornworm, Manduca quinquemaculata. However, the tomato hornworm and tobacco hornworm Manduca sexta, are often confused with each other. They are very similar in appearance and both attack members of the Solanaceae family. The tomato hornworm is three to four inches long at full size (likely to be the biggest caterpillar we see in our gardens) and green in color with white v-shaped marks along its sides. A black "horn" projects from the rear of the caterpillar. Tobacco hornworms have diagonal white stripes and a red "horn."

Life Cycle:

The tomato hornworm represents the larval stage of the hawk or sphinx moth, also known as hummingbird moths. The moths overwinter in the soil as dark brown pupae, then emerge and mate in late spring. They lay their eggs, which are round and greenish-white, on the undersides of leaves. The eggs hatch in four to five days, and the hornworm emerges. It spends the next four weeks growing to full size, after which it will make its way into the soil to pupate.

Signs of Tomato Hornworms:

Tomato hornworms are voracious, munching entire leaves, small stems, and even parts of immature fruit. While they are most commonly associated with tomatoes, hornworms are also common pests of eggplants, peppers, and potatoes. Most likely, you'll notice the damage before you notice the hornworms, because their color helps them blend in so well with the plant foliage. You can also look for their black frass (droppings) on the foliage and around the base of the plant.

Effect on Garden Plants:

Undetected, a tomato hornworm can do a fair amount of damage to its host plant. They have hearty appetites, and can defoliate a plant in a matter of days. If they are detected and removed early on, the plant will recover just fine.

Organic Control for Tomato Hornworm:

Because the hornworm is so large, the easiest and most effective way to get rid of it is to pick it off of plants as soon as you detect it and either squish it or toss it into a bowl of soapy water. A bad infestation can be treated by applying BT (Bacillus thuringiensis). This is most effective when the larvae are small. If it is a problem year after year, try rototilling the soil either in late fall or in spring before you plant--this will either bury the pupae or destroy them. However, if you see a hornworm covered with white egg sacs, leave it be. The egg sacs are those of a parasitic wasp called the Braconid wasp. Let the eggs hatch, and you'll have an army of wasps ready to defend your garden against all types of pests.
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