Army Cutworms Are Active in South Dakota

Written collaboratively by Adam Varenhorst, Philip Rozeboom, Patrick Wagner, and Brad McManus.

Originally Submitted: May 8, 2023

Army cutworm caterpillars have been spotted in winter wheat in central South Dakota. Although they haven’t been extremely active in the last few weeks, their activity will increase as temperatures increase across the state. Army cutworms can rapidly reduce winter wheat stands if large populations are present. Their activity is often discovered by observing patches of winter wheat that start to look like they are thinning out.

Lifecycle and Identification

Army cutworm caterpillars overwinter in winter wheat and alfalfa fields. This allows them to emerge and be active earlier in the spring, and it is the reason that they are often the first insect pests observed in winter wheat fields. Young caterpillars are small and are generally a light green-brown color with relatively few markings. As the caterpillars mature, they develop a dull-gray or gray-brown body that may have mottling (spots or smears of varying colors, see Figure 1).

Caterpillar with brown and black stripes running down the length of its body. The caterpillar has a tan head and is feeding on green plant material.
Figure 1. Army cutworm caterpillar. Courtesy: Joseph Berger, Bugwood.org

Older caterpillars will have several pale stripes that run the length of their bodies. Regardless of age, the caterpillars have brown heads.

Army cutworm caterpillars feed at night and hide just below the soil surface during the day. During overcast days, the caterpillars may remain active. Army cutworms can become active during relatively cool temperatures (around 40 degrees Fahrenheit). The temperature that they are active may be lower in fields with limited ground cover but higher for fields with more ground cover.
Scouting for the caterpillars can be time intensive due to sampling soil, thus management decisions based on detection and characteristic plant injury are recommended. The feeding is characterized as “clipping,” where the caterpillars feed on the plant near the soil surface. This type of feeding can result in ragged patches of plants that appear to be cut or clipped (see Figure 2).

Brown wheat plants that haveobvious feeding injury to them due to cutworm caterpillars.
Figure 2. Wheat injured by cutworm feeding. Courtesy: R. J. Bauernfeind

For winter wheat, the caterpillars tend to feed on the tender blades. Army cutworms generally do not feed on the stem, crown, or meristematic tissues, which allows plants to regrow.

In areas where caterpillars are abundant, they will move from food source to food source “army style.” Management is recommended if large patches of the field have been defoliated, or if 2 to 4 army cutworm caterpillars are observed per square foot.

Management

Injury to winter wheat from army cutworms will be worse for fields that are experiencing moisture stress. If management is necessary, an insecticide application is recommended. Please refer to the latest South Dakota Pest Management Guide: Wheat for a list of products labeled for cutworm management. When applying insecticides for army cutworms, make sure that the forecasted temperatures are at or above 50 degrees Fahrenheit for three to four days after application to ensure that the caterpillars will be exposed to the insecticides.

Related Topics

Wheat Insects

Related Content

A hand holding a brownish gray moth with a valley of green grass and trees in the background.

Army Cutworm Migration Swarms Detected in Western South Dakota

Mass populations of army cutworm moths are being reported to entomologists at South Dakota State University. Thus far, these migratory swarms have only been observed in far western South Dakota, particularly within the Black Hills.

Green wheat leaves with yellow streaks throughout.

Wheat Streak Mosaic Virus Complex: Breaking the Green Bridge

As wheat harvest proceeds, it won’t be long until winter wheat planting is underway in South Dakota. To effectively reduce wheat streak mosaic virus, it is important to manage the green bridge effect to slow spread of disease in newly emerging wheat fields.

Wheat plants infected with wheat streak mosaic virus.

Volunteer Wheat and Kochia Management With Herbicides Will Likely Require Two Passes

Wheat curl mites, which carry wheat streak mosaic virus, use volunteer wheat and grass weeds as secondary hosts to infest recently planted winter wheat crops. Therefore, effective management of these plants before winter wheat planting is critical.