Stalk borer can be a reoccurring pest along the edge rows of corn adjacent to perennial grass borders, waterways, or terraces. The caterpillars move from grasses to corn when the stalk gets too small. Like all insects, they develop based on accumulating temperatures and right now, you could expect to see caterpillars moving throughout the southern half of Iowa.
There is a limited time to make a rescue treatment for stalk borer. Once they find a corn plant to infest, foliar insecticides are not effective. If you have experienced stand loss due to this caterpillar, scout now to make a treatment decision.
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. 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.
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