“Cutworm” is a common name for many caterpillars in the moth family Noctuidae. They are insects (not worms!) that chew, or cut through, plants above or below the soil line in the spring. One notable exception is the western bean cutworm, which occurs later in the season and targets reproductive tissues rather than cutting stems. With recent reports of cutworm activity occurring in Iowa this spring, use this article as a reference while scouting corn, soybean, and forages (or even your garden).
Black Cutworm
Black cutworm is a migratory pest that we track each spring through the Iowa Moth Trapping Network. Although it does not overwinter here, black cutworm caterpillars are a common occurrence in areas with cover crops or other plants. actively growing in the spring.
Black cutworm caterpillars have grainy, light grey to black skin and a dark brown head. They have pairs of dark wart-like bumps along the side of their body – these help distinguish them from dingy cutworms. For black cutworm, the tubercle closest to the head on each segment is about 1/3 the size of the other.
Black cutworm caterpillars prefer to feed on grassy crops or weeds, like cereal rye, turfgrasses, and corn, but they may also feed on broadleaf weeds, soybeans, or other actively growing plants if they are present. You may find irregular holes in leaves, cut stems, or wilting and death from feeding below ground. Larvae are nocturnal, so they hide under residue or in the soil during the day. Caterpillars may drag plant pieces below ground during the day to continue feeding, so you may see a plant that doesn’t quite look right sticking out of the soil.
Bronzed Cutworm
Bronzed cutworm is an occasional pest native to Iowa, but it made an appearance last spring and has already been responsible for plant death in a central Iowa pasture this spring.
Bronzed cutworm caterpillars are dark brown with a bronze sheen and a light brown head. They have three golden yellow stripes down their bodies, and the first thoracic segment behind the head is a bit darker. Bronzed cutworm is more likely to be confused with true armyworm than other cutworms, but pay attention to the overall appearance and head capsule to distinguish them. Like black cutworm, bronzed cutworm is nocturnal, so it may be difficult to detect larvae during the day.
Bronzed cutworm tends to be more of an issue in turfgrass or pasture, but it can be an issue in crops when they are planted in a field that was perennial grassland prior. Symptoms of injury would be similar to black cutworm. In pastures or turfgrass, there may be circular patches of dead plants where larvae have cut the stems or leaves of plants and killed the growing point. This is distinguishable from grub feeding, because grubs only feed on roots.
Dingy Cutworm
Dingy cutworm is also native to Iowa and an occasional pest. Like the previous cutworms, it is also nocturnal and feeds in the same manner. We have received photos of dingy cutworm from western Iowa this spring, but no plant injury was noted. Dingy cutworm larvae are similar in appearance to black cutworm larvae, but the two tubercles on the side of the body are similar in size.
Other cutworms
There are a host of other cutworm species that may be present in fields, including glassy, sandhill and variegated cutworms. Glassy cutworms are pale with a reddish-orange head and have the same body shape as other cutworms. Sandhill cutworms are light tan and semi-translucent with several pale stripes. It will only be found in soil with a high percentage of sand. Variegated cutworms are grayish-brown and mottled, usually with four to seven light spots on the back. Variegated cutworms can feed in a similar manner to other cutworms, but they are known to climb plants at night to feed on foliage and flowers.
Management
Since all of these cutworm species are rare offenders in crop fields, management is not usually required, and we do not recommend preventative insecticide applications for these pests. Instead, scouting for cut or damaged plants early in the season should guide your decision-making. If significant stand loss occurs, consider a rescue treatment if larvae are still active and less than ¾ of an inch long. A dawn or dusk application may be required to make contact with nocturnal larvae.
Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 11, 2026. The information contained within may not be the most current and accurate depending on when it is accessed.
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- Extension Entomologist Specialist
- ANR Crops Team Leader