University of Illinois

No. 22/August 29, 1997

Status of European Corn Borers? Maturity of Corn

Activity of European corn borers continues in some areas of the state. We have received a handful of reports of very large flights of adults in recent days, so these late emergers still pose a threat to corn in localized areas. However, we question if treatment for corn borer control will do any good (economically) in most fields right now. A decision to treat for corn borers at this late date depends upon the maturity of corn. Our management worksheet (issue no. 20 of this Bulletin, August 8, 1997) indicates that the potential economic benefits of treatment decline rapidly if infestations occur after corn reaches the blister stage. A recent report of corn maturity indicated that approximately 25 percent of the corn in Illinois had dented, and 75 percent was in the dough stage. Based upon this information, we could not justify treating any more cornfields to control corn borers.

One other point should be made. In our worksheet, the percentages of yield loss attributed to each corn borer are based solely upon physiological yield reduction. These percentages do not account for stalk lodging or ear drop resulting from corn borer infestations. Many of our modern corn hybrids have strong stalks and ear shanks, but yield losses attributable to an inability to harvest ears on the ground are possible if infestations of corn borers are intense. Because we have no guidelines to accommodate this yield loss, we recommend that scouting for corn borers continue solely to determine if certain fields might be susceptible to broken stalks and dropped ears. If these fields are identified, they should be scheduled for early harvest, if possible.

Kevin Steffey and Mike Gray, Extension Entomology, (217)333-6652