University of Illinois

Update on European Corn Borers

August 14, 1998
Although the numbers are not large, captures of European corn borer moths in at least one trap in Champaign increased recently. John Shaw, coordinator of the Insect Management and Insecticide Evaluation Program at the Illinois Natural History Survey, reported that moth captures in his light trap recently increased from 1 to 2 per night to more than 10 to 20 per night during the first week of August. However, the captures dropped to zero on August 10. In addition, Maria Venditti, my graduate student, and her crew found several freshly deposited egg masses in some corn fields in Sangamon County on August 5.

Although this slight increase in corn borer activity this late in the summer is somewhat surprising, we doubt that this "blip" represents anything significant for field corn. However, we wanted to let you know that people are still monitoring for corn borers. We have received no reports of any significant corn borer activity anywhere else in the state.

Scouting guidelines and management suggestions were offered in last week's issue (no. 20, August 7, 1998) of the Bulletin. Although the threat posed by second- or even third-generation (southern Illinois) corn borers seems insignificant right now, continued vigilance will do no harm. Larvae that infest more mature corn cause less physiological damage than larvae that attack earlier in the season, but stalk breakage and ear drop are always concerns. Recall 1997.

Densities of European corn borers in 1998 will be among the lowest densities we have recorded in the past several years. The weather this year undoubtedly had a profound effect on survival of corn borers, emphasizing once again that densities of corn borers during any given year cannot be relied upon to predict what might happen the next year. Last year's widespread and intense infestations of corn borers were followed this year by infrequent occurrences of corn borers. The reverse could be true in 1999: The low numbers of overwintering larvae could turn into heavy infestations of first- and/or second-generation corn borers if survival is good and the weather is more agreeable. Consequently, farmers who are considering whether or not to invest in Bt-corn need to keep this in mind.

Author: Kevin Steffey