If these grasses are mowed, the cutworms can move to other areas where there are tender, living plants. These caterpillars love to eat grasses, and can build up their populations over the year in the grassy areas around high tunnels. They become active when temperatures are over 40☏, people sometimes report seeing them crawling on the snow. Image: Whitney Cranshaw, Colorado State University, Winter cutworms can be a variety of sizes and colors. They can be a variety of colors, and can be identified by looking for dark dashes running down their bodies. Unfortunately, the caterpillars that do the damage are much less distinctive. Photo: Larry Line, Mostly Moths of Maryland, Winter cutworm adults are large and distinctive compared to the adult forms of other cutworms. The adult form is a distinctive moth, the large yellow underwing. One of the most cold-hardy and early emerging cutworms we see in Minnesota is aptly called Winter Cutworm. If you find damage, try digging around the snipped plants – caterpillars hide in the top few inches of the soil. To find them, you can scout at dawn or dusk. This makes it harder to see the caterpillar culprit, again complicating figuring out who is doing the damage, making it harder to manage.Ĭutworm caterpillars are active at night. Making this more complicated is that caterpillars that feed in this way often hide out in the day and do their damage at night. The fact that cutworm applies to caterpillars that cause a type of damage (eating transplant and young plants, often by snipping them off the base) rather than insects with a similar biology (in terms of when eggs are laid, where they spend the winter, what they eat, etc.) makes it hard to prescribe management recommendations based on seeing cutworm damage alone. There are approximately 10 different cutworms and armyworms species we see in Minnesota that could cause the damage people report. Some of the insects live in Minnesota year-round, while others migrate on weather fronts. “Cutworms” is a label that applies broadly to a large group of caterpillars with a wide range of life histories. Photo: Clemson University - USDA Cooperative Extension Slide Series,. There are many species of cutworm, though they all have a habit of curling up when disturbed. As crops go into high tunnels, now is the time to think about past cutworm problems so we can hopefully catch the culprits and work on the problem in the future. It is always hard to retrace the steps and figure out what caused the damage. We hear from growers in the summer about cutworm issues in high tunnel crops, oftentimes long after the damage has been done.
Originally published in 2022, updated for 2023. Marissa Schuh, Integrated Pest Management Extension Educator.
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