Extension Ag Update
November/December 2003
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Here or Coming? Western Bean Cutworm

Ellen Phillips, Extension Educator – Crop Systems, Countryside Extension Center, 708-352-0109, ephillps@uiuc.edu

Previously a western Corn Belt pest, the Western Bean Cutworm made its presence known in western Illinois this past summer. A monitoring trap set out for one night caught enough moths for scientists to ask the questions, “How long have they been here?” and “Where else are they?”

Despite its name, the Western Bean Cutworm is not only a pest on dry beans but also a late season problem on corn. Feeding on corn ears, it chews and scars the kernels opening up pathways for other pathogens like mold.

Western Bean Cutworms only have one generation a year. The moths emerge in early July. In corn, females lay their egg masses (about 50 eggs) on the upper surfaces of the leaves. Larvae will hatch and begin feeding in 5-7 days and continue feeding for about a month. Due to the mobility of the larva, one egg mass can affect plants in a ten foot diameter around the plant. Once the larva has completed its fifth instar stage, it burrows into the soil where it overwinters in the prepupal state.

Because of the mobility of this pest, scouting and timing of insecticide treatments are critical. To learn more go to www.ipm.uiuc.edu or check out the following websites.

Western Bean Cutworm, in Corn and Dry Beans, University of Nebraska – Lincoln
http://ianrpubs.unl.edu/insects/g1359.htm

Maize Insect Pests of North America
http://ipmworld.umn.edu/chapters/maize.htm

Western Bean Cutworm: Characteristics and Management in Corn and Dry Beans, Colorado State University
http://www.ext.colostate.edu/pubs/insect/05538.html