Cutworms and armyworms: Management decisions

Cutworm and armyworm damage in soybean is not typical. There are a few field conditions that may make soybean fields attractive to egg-laying females:
• Fields planted under reduced or no-tillage practices
• Fair to poorly drained fields
• Fields with winter annual weeds emerged prior to soybean planting
• More likely found in fields previously infested with cutworms and armyworms

Economic thresholds for cutworms and armyworms have not been developed because infestations are unpredictable and infrequent. Treatment decisions must be based on the size of the caterpillar and level of infestation. In some cases of very heavy density, fields may have to be replanted. Check 20 consecutive plants in five different areas of the field to determine percent plant damage. Young cutworms may feed on the stem or leaves, but older larvae can clip off the cotyledons. Also, look for discolored, wilted or dead plants. Cutworms and armyworms will seek shelter during the day, so dig 2-3 inches down in the soil within a row. Consider an insecticide if larvae are less than 3/4 inch long and more than 20 percent of plants are damaged or missing.