What are tomato hornworms?

What is it?

Tomato hornworms are also commonly known as tobacco hornworms. They are of the manduca quniquemaculata and m. sexta species. These worms primarily feed on fruits and foilage and can be dangerous to tomato plants. In the vegetable, tomato hornworms will also attack curcurbit family plants such as cucumbers, muskmelons, pumpkins, summer squash, winter squash and watermelon plants. Hornworms are also known to feed on peppers, tomatoes and eggplants.

Manduca quniquemaculata and m. sexta tend to be very fat 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 ofbrown, grey and black. Tomato 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 they can be whitish or grey. Tomato hornworms can grow to be quite large, and it is not uncommon to see one that is 5 inches in length. Tomato 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 tomato hornworms, regardless of what the damaged tomato plant is, tends to be in the form of chewed on tomato leaves which can be small areas or cover large surface areas of the foilage. Additionally, a sure sign of tomato hornworms are black droppings in piles which soil the leaves, often bending them downward.

How does it manifest?

It takes only a few tomato hornworms to do extensive damage to a crop as each tomato hornworm can consume an excessive amount of foilage in a short period of time. Tomato 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 the undersides of tomato plant leaves each spring after emerging from hibernation and feeding on nectar from a variety of garden flowers. 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 tomato hornworms they have to worry about in a year. However, warmer climates to the south can get anywhere from two to four generations of tomato hornworms per growing season.

What can you do about it?

Tomato which show signs of hornworm damage can be treated with a carbaryl or pyrethrins containing insecticide. Application should be done according to label instructions. Additionally, a bacterial insecticide which contains bacillus thuringeiensis may be useful in combating tomato hornworm infestation and damage. You can also pick off and kill tomato hornworms as you see them. However, if the tomato hornworm has a white sack on it’s back, don’t kill it off. Rather, let the parasitic wasps which are inside the sack kill the tomato hornworm off. Then the wasps can mature, emerge and move on to kill any other troublesome tomato hornworms in the garden.