One crops consultant says 25% or more of the plants in a non-GMO corn field in southeastern Indiana were affected by first-generation corn borer. He filed the report just a few days ago. Typical shot-hole, or bullet hole, feeding of leaves was the primary tip-off to corn borer. That pattern develops because larvae are inside the whorl, and chew through leaves that later unfurl with sets of holes in a straight pattern on one or more leaves.
Non-GMO corn means it does not have genetically-modified traits. Farmers near markets that pay a premium for non-GMO corn still grow a decent amount of non-GMO corn,. It's particularly strong in areas close enough to the Ohio River to ship grain there. Several companies that buy grain and are located with facilities near the river have markets for non-GMO corn. Most of it goes into food channels.
One of the first GMO traits released in corn was the BT cornborer trait. So Bt corn has the ability to protect the plant form significant corn borer damage. Corn borer is not a big problem in Indiana most years. However, in two to three years out of 15, it can be an issue. That chronology was based on the days before Bt corn. It's possible that refuge rows, which are not supposed to contain GMO traits, could be affected by corn borers.
The impact of corn borers year in and year out has become so minimal in Indiana that the Purdue University Entomology Department has discontinued its annual survey of corn borers headed into winter. It was data usually collect just before the end of the season.
The consultant suggests that people with corn at risk should continue scouting their fields for signs of the presence of corn borers as the season unfolds. The biggest threat to corn without Bt gene protection actually comes as second-brood borers emerge from eggs laid by the first brood.
The time frame for catching corn borers with an insecticide on the second-generation time frame is very short. Once borers get into the stalk tissue, or more typically, once they bore into ear shanks, it's close to impossible to control them with insecticides, even with an aerial application. Your only chance of preventing the second brood from injury is to scout and catch them just as the injury occurs.