Traditionally, entomologists say corn borer is not as big of a problem in Indiana and the Eastern Corn Belt as in the Western Corn Belt. That's why when GMO traits to control corn borer first appeared from seed companies, they were positioned first in the western side of the Corn Belt. Indiana only sees a large infestation on average only a few years out of 20.
This could be one of the years for corn borer impact in non-GMO crops which don't have protection from corn borer.
Danny Greene of Greene Crop Consulting, Franklin, says he has several clients who grow non-GMO corn, often because they get premiums for various food-related markets for non-GMO corn. He found a considerable amount of indication of corn borer earlier when the first generation was active.
"It definitely was more than normal," Greene says.
He says by his calculations spraying would have paid in many fields. Some growers sprayed, but many didn't. Some didn't scout close enough or consult with him or someone else to know it might be an issue.
Earlier in the season, shot-hole damage, a series of small holes across the leaf in one spot, indicates feeding damage. The pattern forms because larvae feed while leaves are still in the whorl. When they unroll and open up, they display the feeding holes larvae made chewing their way through wrapped-up leaves in the whorl.
The concern now is second generation corn borer. They're the larvae that can tunnel into stalks and ear shanks. You can scout for them, but spraying is more difficult at this point. The borers are often inside the stalks and are not as likely to be covered by spray applications.
There are threshold guidelines that a Purdue University Extension person can help you work through to determine if an application of insecticide might be warranted.