Thirty-four sites reported this week. Eleven of the sites had European corn borer (ECB)-E and three sites had ECB-Z. Eighteen sites reported corn earworm (CEW) with eleven high enough to be on a 5 or 6 day spray interval (see table at bottom of post). Fall armyworm (FAW) moths were caught at five sites and Western bean cutworm (WBC) was caught at eight sites. The hybrid ECB moth was caught at both the Hurley and Geneva site.

Western bean cutworm numbers are beginning to go up this week with peak flight expected late July into early August. It is important to begin scouting for egg masses even if cumulative trap catches have not reached 100, as egg masses have been found when cumulative trap catched were still in the single digits. WBC will usually lay eggs on the upper side of the top 1-3 leaves of pre-tassel corn, close to the leaf base. After tasseling has finished WBC seek out younger corn or dry beans. To scout for egg masses check the top 3 leaves of ten corn plants in ten locations throughout the field. The eggs are easy to observe if you view the leaf while holding it towards the sun. The egg mass will appear as a distinct shadow (see photo).

It takes between 5-7 days for eggs to hatch. It is critical that sprays are timed before the larvae have a chance to enter the ear. The egg mass will become purple in color approximately 24 hours before egg hatch (see photo).

WBC emergence is forecast to be at 25% when 1319 degree days (base 50°F) have accumulated beginning on May 1st (see table below). The degree day accumulation (May 1st, base 50°F) for sweet corn trap network sites ranges from 869-1193.

Percent WBC moth emergence, data from
University of Nebraska