Western Bean Cutworm Update

Bryan Jensen, UW Extension and IPM Program

Based on degree day accumulations, DATCP’s Pest Bulletin reports and individual calls, the time for Western Bean Cutworm scouting is here for southern Wisconsin and soon will be in all corn growing areas of Wisconsin. Corn development is catching up to Western Bean Cutworm phenology and soon will soon be susceptible to injury. Some background information was given in last week’s WI Crop Manager. However, this week I could like to make a few comments on scouting and management.

Scout all susceptible corn regardless of above ground traits. Traits will vary on their susceptibility, however, the Vip3A protein appears to have the best efficacy for Western bean cutworm. For more information regarding the presence of proteins in the different trait families consult the Handy Bt Trait Table that Dr. Chris DiFonzo, Michigan State University, updates annually.

Treat when 5% of the plants have egg masses and/or young larvae but before larvae infest the ear. Eggs masses are usually laid on the upper leaf surface on the upper most leaves. Recognition of egg masses is assisted by the shadow they create when backlit by the sun. Larvae, after hatching, are very small and hard to see. After hatching they consume most of the egg shell before dispersing. This makes identification of egg masses difficult.

Timing of an insecticide application is important, but difficult because of the extended flight and egg laying period. Insecticide applications will not kill unhatched larvae nor will they kill larvae that have already entered the ear. Therefore, applications should be made when corn is most susceptible (tasseling) and when eggs are beginning to hatch so that larvae encounter a lethal concentration soon after hatch.

Building a field history can be important for future planning. Monitor fields prior to harvest to confirm recommendations, control efficacy and to assist with planning for next year. Look for kernel damage, exit holes from the ear. Bird damage may also be a sign of a recent infestation.

Western Bean Cutworm. Photo credit: Frank Peairs, Colorado State University, Bugwood.org