GMO traits in corn protect against aboveground insects. With so much of this corn grown over the past couple of decades, perhaps European corn borer has said goodbye to Indiana. “No, that would just be wishful thinking,” says John Obermeyer, Purdue University Extension entomologist. “It’s very much alive and well. It’s more of a threat to non-GMO corn in some years than in other years.”
Why is corn borer still around? “There is no danger of it disappearing, because it has such a wide range of different host plants that it can feed on,” Obermeyer says. “If susceptible corn isn’t available, it will turn to weeds, including ragweed and marestail, and survive just fine. Corn borer is also attracted to some of the heavy-stemmed, warm-season grasses, and even to apples.”
The bottom line is, if you grow non-GMO corn, there’s an adequate supply of corn borers available to attack it, Obermeyer says. However, potential damage can vary from year to year. The threat of corn borer is bigger some years than in other years.
Scout non-GMO corn
Corn borer has been prevalent enough in recent years to justify scouting for it if your corn doesn’t have trait protection for aboveground insects, Obermeyer says. There are two generations of corn borer per year — three in some years.
First-generation moths are attracted to the earliest-planted corn around, he says. “Watch for the shot-hole feeding, which occurs as larvae chew through plants in the whorl,” Obermeyer says. Refer to the Purdue University Corn & Soybean Field Guide for tips on scouting and determining if treatment is warranted.
“Treatment for first-generation corn borers can be very effective, as long as you spray before the larvae enter midribs of the leaves,” he says. “Once they burrow into the stalk, spraying won’t be effective.”
When moths emerge and look for egg-laying sites for the second generation, they typically prefer later-planted corn, which might still be pollinating. “The second-generation larvae are the ones that bore into the stalk,” Obermeyer says. “They’re much tougher to control at this stage.”
Left unchecked, corn borers can tunnel into the connective tissue at the base of the ear and lead to dropped ears in the fall.
“Your best bet is to scout and control them during the first generation if there is enough insect pressure to warrant treatment,” he concludes.
Check out the slideshow to see examples of corn borer in its various stages and the damage it can cause.