People who have started farming in the last 20 years haven’t experienced devastation from corn borers because they’ve had good control of this corn pest. However, with some farmers now not using Bt traits, they’re asking questions about the biology, life cycle and management of European corn borer.

The widespread planting of Bt corn hybrids allowed a generation of farmers to grow up without having to think about managing for European corn borer. These hybrids have been extremely effective in keeping European corn borer from impacting corn yields, a far cry from the estimated $1billion annually the pest was costing farmers in yield losses plus control costs.

More farmers now plant non-Bt corn
Today some farmers, in an effort to lower costs as commodity grain markets remain low, have started planting corn without the Bt traits that have proven so effective against European corn borer and other caterpillars.

“Widespread use of the Bt traits for controlling corn borer has meant that farmers haven’t experienced losses from corn borers in a long time,” says Erin Hodgson, Iowa State University Extension entomologist. “People who have started farming in the last 20 years haven’t experienced devastation from corn borers because they’ve had very good control of this corn insect pest. With some farmers now backing off using Bt traits, they are asking questions about the biology, life cycle and management of European corn borer.”

New experience for some
With this pest still active and prevalent, Hodgson has authored a new ISU Extension and publication titled Ecology and management of European corn borer in Iowa field corn, CROP 3139. The publication provides information about the insect to farmers who are encountering this pest for the first time.

The new publication discusses life cycle, biology and egg laying of European corn borers, as well as plant damage and yield loss. How to manage the pest if not using Bt traits in seed is also covered in depth.

Use a scouting program
“If a farmer decides not to use the Bt traits, then they will have to incorporate an extensive scouting program,” Hodgson says. “Farmers must be very proactive, because corn borer is such a devastating pest. Management must target the eggs and small larvae before they are able to move into the ear. Once they enter the ear, there is nothing that can be done. Scouting and quick decision-making is very important because the eggs and larvae are exposed for a limited amount of time.”

Worksheets on how to scout and the management decisions that should be made are included in the new ISU publication. Also included is a table to track the life cycle of European corn borer based on accumulating degree-days. Degree-days are the average number of degrees above the developmental threshold occurring each 24-hour period.

“We need to have some sort of assessment of adult European corn borer activity,” says Hodgson. “Using degree-days is the most accurate way to track development.”