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Corn+Soybean Digest

Scouting European Corn Borers

Today, many growers are using Bt technologies to control European corn borer. However, for growers who didn't plant hybrids with such traits this season, dealing with these yield-robbing pests can be a challenge. "Proper scouting is essential to managing European corn borer infestations," says Steve Hyronimus, District Agronomist, Mycogen Seeds. "The flights of the moths vary each year due to differing crop stages and weather conditions. Typically, flights begin the middle weeks of June and last for two to three weeks. This year's early planting will push the schedule ahead for scouting."

Moths normally will sit in the grassy field margins until the corn plants are taller. Moths seek out the tallest, most mature plants first. Begin scouting when the top corn leaf can be stretched to reach 18 in. tall. The natural toxin DIMBOA, produced by the corn plant, will ward off larvae feeding before this height is reached. Eggs don't seem to attach well to the corn plant until corn is taller.

Moths like tall grass and shelterbelts to hide in during the daytime. In the evening hours, they deposit their eggs on the underside of corn leaves. Moths prefer warm nights for egg laying while windy, rainy nights decrease their activity. Eggs hatch in four to nine days, depending upon the temperature. Larvae feed first in the whorls of the corn plant; so look for shot-holing in the youngest leaves.

Randomly pull out the whorls from 10 plants in five locations in the field. Count the 1/8-1/4 in. long black-headed larvae in the whorl. Input this number into one of the various formulas to estimate threshold for treatment.

"Treatment of the 1/8-1/4 in. larvae is the most desirable stage," Hyronimus concludes. "Larvae at 3/8 in. are soon going to tunnel into the whorl and control measures will then be ineffective. Scout weekly until egg masses are located and then scout every three to five days."

For more information contact Stephen Smith, Agronomy Services Manager with Mycogen Seeds, at 317-337-4662 or via e-mail at

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