Integrated Crop Management

Western bean cutworm hits northwest Iowa

The western bean cutworm is a late-season pest of field corn that we rarely see in Iowa. Tony Weis, ISU Extension specialist in field crops, first pointed out some of the problems this year that farmers are experiencing from this moth in northwestern Iowa. One field in Holstein, Ida County, had approximetely 95 percent of the ears heavily damaged from the larvae. Kernels in the ear tips, plus along the side of the ear, were consumed or heavily scarred. In addition to this loss of grain, many plants were invaded by ear molds, which reduce the quality of the yield at harvest.

Corn ears damaged by western bean cutworm.

The photograph above shows three ears collected from this field. Other reports have come from Greg Peters, Cargill Hybrid Seeds, who indicated that fields in Lyon and Sioux counties were heavily damaged by this insect. Dick Pence, Novartis Seeds, reports finding western bean cutworm in Carroll, Cherokee, Plymouth, and Shelby counties. Western bean cutworms typically cause damage in western Nebraska and eastern Colorado but during some years they do move farther east.

This insect can be distinguished from the corn earworm by dark stripes immediately behind the head, and the absence of small dark spines or stripes on the side of the body. There is only generation per year and larvae drop to the ground to spend the winter. It is unlikely that any western bean cutworms can still be found in the ears in mid-September, but their damage will be evident until harvest.

Western Bean Cutworm.

The western bean cutworm may be one insect to monitor more closely next year, particularly if we have a mild winter that enhances survival of the larvae.

This article originally appeared on page 163 of the IC-484(22) -- September 18, 2000 issue.

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