Originally Submitted: June 10, 2021
Dingy cutworms have been reported in South Dakota soybean. Although they are not normally a major pest of soybean, dingy cutworms will often defoliate soybean leaves and can cause significant stand reductions by cutting plants (Figure 1). Dingy cutworms are often more abundant in no-till fields with high residue present.
Identification
Dingy cutworm caterpillars are nocturnal and can be found by digging 1-2 inches in the soil around cut plants. They get their name due to their dull brown to gray coloration. These cutworms have a distinct pale gray line that runs down the center of their bodies. The dingy cutworm caterpillars have spots (tubercles) present on the sides of each body segment that are all similar in size to one another (Figure 2). They also have two dark lines on their brown head capsule.
Scouting and Management
Cutworms tend to be more of an issue in soybean fields that have been planted under reduced or no-tillage practices, fair to poorly drained fields, or fields with weed or cover crop presence prior to planting. Cutworms can be scouted by examining fields for cut plants and by digging in the soil near cut plants to determine population densities.
To scout for cut plants, examine 20 consecutive plants in five locations throughout the field (100 plants per field). In addition to looking for cut plants, also examine plants for signs of defoliation as younger cutworm caterpillars may be incapable of cutting the plant. In areas where cut plants are observed, dig in the soil within the row to find any caterpillars that may be present.
Insecticide management should be considered if 20% or more of the scouted plants are cut and the caterpillars are less than 3/4 of an inch or shorter in length. Caterpillars this size will continue to feed on plants and may further reduce stands. Please refer to the current edition of South Dakota Pest Management Guide: Soybean for a list of insecticides labeled for the management of dingy cutworms in soybean.
