With the generous cooperation of the crop systems and IPM Extension educators, the impact of European corn borers was assessed in 51 Illinois counties (approximately 500 cornfields) this past fall. Results of the 2002 and 2003 fall European corn borer surveys are presented in Table 4. The results from the most recently completed survey continue to reveal a long-term pattern of very low overwintering densities of this insect pest. In 2003, the average percentage of plants (statewide) infested by European corn borers was 32.5%, and the average number of corn borers was 0.52 per plant. These numbers represent a very low infestation of corn borers that Illinois producers had to contend with during the 2003 growing season. In addition, these numbers suggest that a very small moth flight will occur next spring. Ultimately, the level of diseases (Nosema pyrausta and Beauveria bassiana) in overwintering larvae and environmental conditions during the first flight of moths next spring will be the key factors in regulating European corn borer populations in 2004. As producers make their seed-selection choices this winter, we hope our survey data on overwintering densities of borers can be of some value in decision making.
From time to time, we're asked questions about how the survey is performed. Because it always has been conducted using the same sampling procedures, we can compare one year with the next. European corn borers are surveyed by selecting a cross-section of 10 fields throughout a county. Within each field, 25 consecutive plants are checked for any signs of corn borer injury (frass, exit holes, broken stalks). Surveyors make sure that the 25 plants are not within border rows and try to check plants 25 to 30 paces away from these field margins. After the number of plants infested is determined, two infested stalks are split and the borers are counted. County and statewide averages are then calculated for percentages of plants infested and numbers of borers per plant.
If you have any questions about the results of this survey, please give us a call or send us an e-mail message.--Mike Gray and Kevin Steffey