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Controlling tomato hornworm

Hornworms can be very destructive, but are fortunately easy to control

If something is munching on your tomato plants, it might be a tomato hornworm. Hornworms are large, green caterpillars with a “horn-like” tail that gives them their name. They can grow up to four-inches in length, have voracious appetites, and will eat everything on the plant but the stem. But if there are enough caterpillars, they’ll eat the stems too.

Rick Weinzierl is an extension entomology specialist at the University of Illinois. He says hornworms can appear on your tomato plants at any time.

"The moths fly in early to mid-summer. But, the time that a moth comes out of a pupa and starts to lay eggs for that single species in that single generation is spread over quite a bit of time. So you will see the first hornworm damage with a little hornworm, and six-weeks later you may see yet some more little hornworms," says Weinzierl. "It’s not a new generation, it’s just that they’re spread out, they don’t all come out at one time."

Hornworms are easy enough to see that you can pick them off by hand and toss them into a bucket of soapy water to kill them.

But, if you have many tomato plants, you may need chemical control. Don’t wait until the critter is four-inches long. Weinzierl says as soon as you notice defoliation and know the caterpillar is your culprit, start your treatment.

"This is the easiest insect in the world to control with all the BT products, the Bacillus thuringiensis ones. Whether you are an organic grower or not, you probably would choose it because it will not directly kill any of the parasites, it won’t kill the predators of aphids, it won’t do other bad things," says Weinzierl. "So use an insecticide that kills who you’re after, but not everybody else."

Lady beetles and green lacewings are natural enemies of the critter and often prey upon the egg stage and on young caterpillars.

Learn more about tomato hornworms and how to deal with them

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