By Ashley Dean and Erin Hodgson
Stalk borer is an occasional pest of corn, but it can be persistent in some fields, especially those fields near perennial grasses that serve as overwintering sites (fence rows, terraces, and waterways are typical sites). Tracking degree days is a useful way to estimate when common stalk borer larvae begin moving into cornfields from their overwintering hosts. Foliar insecticide applications are only effective when larvae are migrating and exposed to the insecticide. Stalk borer activity is ahead of schedule this year with larvae on the move across much of the state (Figure 1); therefore, scouting for migrating larvae should begin now to make timely treatment decisions. Movement begins when 1,400 growing degree days (GDD; base 41°F) have accumulated since January 1, and peak movement occurs at 1,700 GDD.
This encyclopedia article details stalk borer identification, sampling, and management, and provides information on high-risk fields. Stalk borers tend to re-infest the same fields, so prioritize scouting fields with a history of stalk borers, paying close attention to field edges. Finding “dead heads” in nearby grasses or weeds is an indicator of stalk borers in the area (Photo 1). The larvae are purple with white stripes and a dark saddle across the middle of the body (Photo 2). They are not highly mobile and typically only move into the first four to six rows of corn. Young corn is particularly vulnerable to severe injury; plants are unlikely to be killed once they reach V7 (Photo 3).
Source : iastate.edu