Preliminary Report on the 1999 European Corn Borer Fall Survey

October 4, 1999
Results from the preharvest European corn borer survey have been reported for 16 counties. Our thanks go out to the IPM and Crop Systems Extension Educators who have generously contributed their time to this effort! The preliminary results of this survey are offered in Table 1. When the survey is complete, we should have results from 17 additional counties, which will provide a more complete picture of the magnitude of the European corn borer infestation in 1999. More importantly, results from this survey may assist producers as they begin to make seed-selection decisions for the 2000 growing season.

What do these numbers suggest for 1999 and 2000? For anyone who monitored European corn borer moth flights or scouted cornfields for larvae, these numbers are not likely to come as a surprise. This past growing season will not be remembered for the severity of corn borer injury (perhaps just the opposite). The average percentage of plants in a county that exceeded an infestation level of 50 percent was exceeded in only one instance, in Washington County. Most counties were far below infestation levels associated with potential economic losses. Ten of the sixteen surveyed counties had infestation levels below 25 percent. These data also suggest that the overwintering population of European corn borers will be very low. Keep in mind that the number of borers per 100 plants is based on a preharvest sample of infested stalks. After stalks are shredded through a combine, far fewer borers will be present across the Illinois landscape. After we have completed the fall survey, we'll provide a final estimate of overwintering populations in Illinois. At this moment, the likelihood of an impressive first flight of European corn borers next spring seems unlikely. Producers are encouraged to look at these data when making a decision regarding the purchase of a Bt hybrid versus a non-Bt hybrid for the 2000 growing season.

A final thought: the originators of the fall European corn borer survey soon discovered that the correlation of fall corn borer survey data with injury the following season was poor. Often large overwintering populations of corn borers succumbed to diseases such as Beauveria bassiana and Nosema pyrausta, resulting in low densities of first-generation corn borer the following spring. In certain instances, small overwintering populations of corn borers suffered little mortality through the winter and were greeted with spring weather patterns ideal for moth emergence, mating, egg laying, and larval survival. So it really is a tough call to predict economic infestations of European corn borers. However, with the very low population of corn borers on hand, a series of factors must come together to result in even a moderate infestation of borers in 2000.--Mike Gray, Kevin Steffey

Author: Kevin Steffey Mike Gray