Tobacco hornworm, a common pest in Maine that is known for attacking tobacco and tomato plants. Credit: Courtesy of Griffin Dill | University of Maine Cooperative Extension

If you planted tomatoes in your garden this year, now is the time to go out and give those plants a thorough inspection. Depending on what’s lurking in their foliage, you may need to pick off tobacco hornworms now if you want to pick ripe tomatoes later.

“You look at your garden all summer and nothing is wrong and then one morning there’s this worm eating your tomatoes,” said James Dill, pest management specialist with the University of Maine Cooperative Extension. “I’ve had one or two [worms] sent in already for identification.”

Tobacco hornworms will destroy the plants before the fruit even has a chance to ripen. They are a common, albeit unwelcome, pest which feed on plants in the family Solanaceae. These include eggplants, pepper plants and tomatoes. In Maine, they seem particularly fond of the tomatoes and thanks to their voracious appetite, they can strip a plant clean almost overnight in what can appear to be a sneak attack, according to Dill.

“Usually a tomato plant has so much foliage so most people don’t even see the hornworms at first,” he said. “Then all of a sudden the plant is stripped down to nothing.”

Given that the hornworms can grow to be the size and length of an adult human’s ring finger, Dill said people are often surprised how hard they are to find in and among tomatoes or other vegetables due to their effective camouflage.

Hornworm caterpillars are bright green with white diagonal stripes on their bodies. They have a small, pointed horn-like structure at the base of their body which gives them their name. They can grow to nearly four-inches in length.

The best way to find a hornworm caterpillar is to look for its droppings, or “frass” as larval insect larvae is called.

“The frass will look kind of green and wet,” Dill said. “Once you see little or big piles of that you want to look right above it and that is where the hornworm will be.”

The best method of ridding a garden of the pests, according to Dill, is hand picking them one-by-one off the plants and disposing them.

“You can throw them away any way you want to,” Dill said. “Some people say they make great fishing bait, so if you are a fisherman, you could use them for that.”

The most common method of disposal is dropping the caterpillars into a bucket of soapy water, which will kill them.

Biological control is another method for dealing with the hornworms. For this method, Bacillus thuringiensis — or Bt — a naturally occurring bacterium found in the soil that is commercially available as a pesticide, is used. Bt is safe to use around pollinating insects and suitable for organic gardens.

The mature hornworm caterpillar tunnels down and nests for the winter near tomato plants and emerges from the ground the following year as the adult moth. Dill said deeply tilling all soil around the garden can kill those pupating moths before they fully develop.

That, he said, is about the only preventative method in dealing with the hornworm caterpillar.

In Maine, the hornworm caterpillar is around for about three weeks in July into August, and the good news is that despite the damage they can do to a tomato crop, they pose no danger to humans or pets.

And there’s more good news: While they are a nuisance that should be addressed as soon as they are detected, this summer’s crop of hornworms is no worse than previous years.

Julia Bayly

Julia Bayly

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.