Often there is a dark spot on the side of the body just above the second true leg. The body surface is smooth and almost hairless. As they grow older, larvae disperse and move toward the center of the plant. Beet armyworms build up as weather warms and are most common on late summer and fall crops. However, serious economic damage to cole crops is uncommon.
Seedlings are very susceptible to beet armyworm damage.
Treat if you find one second or third instar larva for every 10 plants. Sample for armyworms at the same time you are sampling for loopers and cabbageworms and include them in your total counts for caterpillars. It is not usually necessary to treat older plants between thinning and heading. Treat just before heading if caterpillars are in the field. Beet armyworms are more difficult to control with insecticides than loopers and cabbageworms, so be sure to make note of their presence in your monitoring records.