By Scout Nelson
Reports of dingy cutworm activity in soybean fields have increased across parts of Central South Dakota. These insects are commonly present during spring but usually remain at low levels. When weather and field conditions are favorable, they can become significant pests and cause serious damage to young soybean plants. They may also affect corn, wheat, and sunflower crops.
Information shared by Adam Varenhorst, Associate Professor and SDSU Extension Field Crop Entomologist, along with Patrick Wagner and Philip Rozeboom, highlights growing concerns about dingy cutworm feeding in soybean fields as well as corn, wheat, and sunflower this season. The pest is often more common in no-till fields where large amounts of crop residue remain on the soil surface.
Dingy cutworms feed mainly at night, making them difficult to detect during the day. Producers often find evidence of their presence through cut or damaged plants. The caterpillars usually hide under plant residue or in the soil near affected plants. They are dull brown to gray in color and have a pale gray line running down the center of their bodies. Their head capsule contains two dark lines, which help distinguish them from other cutworm species.
Fields with reduced tillage systems, heavy residue, poor drainage, weeds, or cover crops before planting are often at greater risk for infestations. Because the caterpillars remain hidden during daylight hours, scouting is important for determining whether management actions are needed.
Crop specialists recommend examining 20 consecutive plants in five different areas of a field, for a total of 100 plants. Producers should record the number of plants that are cut or heavily damaged. In areas where injury is found, digging into the soil near affected plants can help locate the caterpillars and estimate population levels.
Management decisions depend on both plant injury and caterpillar size. Insecticide treatments may be justified when 20% or more of the scouted plants are cut and the caterpillars are less than three-quarters of an inch long. Smaller caterpillars continue feeding and can cause additional stand loss.
Please refer to the current editions of the South Dakota Pest Management Guides for a list of insecticides labeled for the management of dingy cutworms.
Photo Credit: Manitoba Agriculture
Categories: South Dakota, Crops, Corn, Soybeans, Wheat