Stalk Borers Moving in Southern Iowa
Tracking degree days is a useful tool to estimate when common stalk borer larvae begin moving into cornfields from their overwintering hosts. Foliar insecticide applications, if needed, are only effective when larvae are migrating and exposed. Start scouting corn for larvae when 1,300-1,400 degree days (base 41°F) have accumulated. Southern Iowa counties reached this important benchmark over the holiday weekend (Figure 1), and therefore scouting for migrating larvae should begin now to make timely treatment decisions. Stalk borer larvae in central and northern Iowa will migrate later in June.