Source: John Tooker, Entomology Specialist, Penn State University

With the wet, cool spring, corn planting in some parts of Pennsylvania has of course been delayed a bit. No-till growers with small grain cover crops should remain aware of true armyworm because it poses a risk to the corn crop when the window between spring burndown and corn planting is too short (less than two weeks). This is good to keep in mind because growers can get anxious about getting their crops in the ground and may lose sight of the importance of waiting long enough between burndown and planting.

Adult moths fly into Pennsylvania after overwintering in the soil in states to our south. Females often lay their eggs on grass weeds or small grains and move to corn when weeds or grain cover crops are killed with herbicides. Armyworm can occasionally cause problems feeding on small grains sowed for harvest, but tend to be problematic more often in corn when small grains are killed with herbicides because armyworms move to young corn plants. Armyworms tend to feed at night along the margins of corn leaves, avoiding midribs. During the day, larvae hide in leaf sheaths or in the soil or leaf litter. Rescue treatments are usually the most efficient and economical tactic for managing true armyworm because populations are very spotty and preventative applications may not have sufficient residual activity to kill caterpillars that hatch out later. Armyworms can warrant treatment should infestations reach 25 percent of plants in a field. A recently revised fact sheet provides more information on armyworm