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Black Cutworm Monitoring

The black cutworm is an early nemesis of corn and even soybean growers. Moths overwinter in the South and ride the jet stream north to the Corn Belt in early spring. Females lay their eggs on anything green in and around the field including weeds and cover crops. The caterpillars are a grayish-brown in color, can grow to over an inch long, and they have an insatiable appetite.

Erin Hodgson is an Extension entomologist at Iowa State University. She says the time to scout for cutworms is when corn and soybean plants germinate and pop out of the ground.

"These cutworms can, as the name suggests, cut the top of the plant off at the soil line. Sometimes it’s just a bit of defoliation, like pieces missing, or it can be more severe in which they just outright kill the plant," says Hodgson. "So, if they chop off the top of the plant, it’s just going to kill the plant."

When you walk into a field and see defoliation you probably won’t see the caterpillars because they feed at night. Cutworms are skittish during the day and will find cracks and crevices to hide in. Hodgson says you’ll have to do some detective work to find them.

"Getting inside of the whorl of the corn plant, so pulling it apart to see if there’s any activity, or just kind of digging through cracks and crevices to see," she says. "So, if you’re noticing pieces are missing or plants are missing, be looking in and around plants."

Finding just a few cutworms shouldn’t be a cause for concern. However, Hodgson says if you estimate three-to-five-percent of the plants are affected, it’s time to spray a foliar insecticide and the earlier the better. The larger the caterpillars grow, the more damage they do.

Find more tips on scouting for cutworms

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