European Corn Borer Population in Illinois Near Historic Low

November 5, 1999
The 1999 preharvest survey (34 counties) of European corn borers revealed densities that approached near record lows. How low? Statewide averages indicate that only 24.3 percent of corn plants were infested with European corn borers this past growing season, and overall, only 0.29 borers per plant could be detected prior to harvest. After combines "chew" through stalks during harvest, survivorship of borers further declines. If you factor in corn borer diseases such as Beauveria bassiana and Nosema pyrausta, very few moths should be expected to emerge next spring.

How do the 1999 population estimates compare with previous years? Fall surveys of European corn borers have been conducted 55 times, beginning in 1943. With the exception of two years, 1997 and 1998, the fall survey has been conducted by the University of Illinois and the Illinois Natural History Survey. During this half-century of survey work, corn borer densities have been lower in only 2 years, 1982 (0.26 borer per plant) and 1992 (0.27 borer per plant). For the 55-year period, the grand average for the number of borers per plant is 1.19. So the 1999 preharvest density of European corn borers is four times below the grand average. Densities of corn borers in 1983 and 1993, years following very low fall populations of borers, were both below average. In 1983 and 1993, densities of corn borers were 0.53 and 1.10 borers per plant, respectively. If the past can be relied on to predict the future (and this is arguable for insect populations), the 2000 growing season should begin with a spring flight of European corn borer moths that is likely to be at reduced levels for most areas of the state. The information provided in Table 1 shows averages for the percentage of plants infested and the number of borers found per plant for 34 Illinois counties.

Producers are encouraged to review fall corn borer survey data for their respective county and region as at least one factor in deciding whether or not to purchase a Bt hybrid for the 2000 growing season. We thank the following University of Illinois Extension Educators for their generous assistance in conducting the 1999 European corn borer survey: Dale Baird, Robert Bellm, Suzanne Bissonnette, Dennis Bowman, Bill Brink, Kyle Cecil, Greg Clark, Michael Crisel, Stanley Eden, Dennis Epplin, Pete Fandell, David Feltes, Rhonda Ferree, John Fulton, Dido Kotile, Greg Letterly, Matt Montgomery, Jim Morrison, Ellen Phillips, Mike Roegge, and Joe Toman.--Mike Gray and Kevin Steffey

Author: Kevin Steffey Mike Gray