what are tobacco hornworms?

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Large green or horned worms on your pepper plants? Could be manduca quniquemaculata or m.sexta, the tobacco hornworm. Learn more about this garden pest.

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What is it?

Tobacco hornworms are also commonly known as tomato hornworms. They are of the m. sexta and manduca quniquemaculata species. These horn worms  primarily feed on the fruits and the foilage of pepper plants and can be dangerous to other vegetables in your garden such as cucumbers, muskmelons, pumpkins, summer squash, winter squash and watermelon plants. Hornworms are also known to feed on both tomatoes and eggplants.

What does it look like?

M. sexta and Manduca quniquemaculata  tend to be extremely fat, even chubby worms that can vary in color. Often they are green, a bright color similar to the leaves and foilage on the plants from which they feed, however they have also been known to be shades of brown anywhere from dark brown to a light tan. Tobbaco hornworms get their name from the “horn” which protrudes from the rear end of each worm. Typically this horn is either red or black, but occasionally the horn can be whitish or grey depending on the background body color of the insect.

Hornworms can grow to be quite large, and it is not uncommon to see one that is up to 5 inches in length. Hornworms are distinct due to their rear end horn, but also because of their diagonal stripes which criss-cross their bodies. These stripes are usually white or greyish. Damage from tobacco hornworms, regardless of what the damaged plant is, tends to be in the form of chewed on leaves which can be small areas or cover large surface areas of the foilage. Additionally, a sure sign of tobacco hornworm damage are black droppings in piles which soil the leaves, often bending them downward.

How does it manifest?

It takes only a few hornworms to do extensive damage to a crop as each hornworm can consume an excessive amount of foilage in a short period of time. Hornworms hatch from eggs laid by their adult form, a large gray or brown moth with yellow and white markings. These adult female moths lay their eggs on petunias and other garden flowers, which they drink the nectar of to sustain themselves. The adult female moths then lay their eggs on the undersides of the garden flower foliage and hornworms hatch and begin to feed, migrating to pepper plants and other plants that suite their tastes.

When the young hatch they feed for about a month and then crawl into the soil where they pupate. They emerge as full grown moths and repeat the cycle of reproduction. Northern regions in the United States typically only get one generation of tobacco hornworms they have to worry about in a year. However, warmer climates to the south can get anywhere from two to four generations of m. sexta and manduca quniquemaculata  per growing season.

What can you do about it?

Pepper plants which show signs of tobacco hornworm damage can be treated with a carbaryl or pyrethrins containing insecticide. Application should be done according to label instructions and followed carefully. Additionally, a bacterial insecticide which contains bacillus thuringeiensis may be useful in combating tobacco hornworm populations.

You can also pick off and kill tobacco hornworms as you see them, but be careful to be a decent distance away as they tend to squirt quite a distance if smushed. However, if the tobacco hornworm has a white sack on it’s back, don’t kill the hornworm. Rather, let the parasitic wasps which are inside the sack kill the tobacco hornworm off. Then the wasps can mature, emerge and move on to kill any other troublesome hornworms in your flower and vegetable gardens.