Degree days are a useful tool to estimate when common stalk borer larvae begin moving into cornfields. About 10 percent of larvae begin moving to corn after accumulating 1,300-1,400 degree days (base 41°F). Degree days have been slowly accumulating this spring, and southwestern Iowa reached this important benchmark this week (Fig. 1). Scouting for migrating larvae in corn should begin now to make timely treatment decisions.