Seventeen sites reporting this week. European corn borer (ECB) numbers remain low for the season. ECB-E was caught at three sites and ECB-Z at only one site. Two sites caught corn earworm (CEW) both high enough to require a 6 day spray schedule (see table at bottom of post).  Fall armyworm (FAW) was caught at only one site this week. The first report of Western bean cutworm (WBC) occurred this week in Batavia.

ECB damage and larvae were seen this week in whorl stage corn. When scouting focus on the emerging tassel. Separate the leaves and look down into the tassel for any signs of feeding, frass or larvae (see photos). The threshold for ECB and FAW is 15% infested plants at tassel emergence.

Larvae feeding in the whorl are protected from insecticide applications and mortality will not be as high as at tassel emergence, when larvae feeding in the emerging tassel are exposed to the spray.  Larvae will leave the tassel as it opens up and no longer provides a moist, protected feeding environment, and move down the plant looking for protected places to feed.  Insecticide applications need to be timed to kill larvae before they bore into a new feeding location where again they will be protected from sprays.  In fields with very uneven development, two applications may be necessary, one when approximately 25-50% of the tassels have emerged, and again after 75-100% of the tassels have emerged, if the field is still over threshold.

J.W. Apple, Department of Entomology, University of Wisconsin-Madison