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Stalk Borers Are Migrating to Corn
Iowa Ag Connection - 06/07/2023

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 sources). 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. Start scouting corn for larvae when 1,300-1,400 degree days (base 41°F) have accumulated. Most of central and southern Iowa has reached this benchmark (Figure 1); therefore, scouting for migrating larvae should begin now to make timely treatment decisions.

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).


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