An increase in conventional corn acreage due to lower commodity prices apparently favored larval populations this fall. The 75th annual survey in September and October found a state average of 0.11 borer per plant, an increase from last year’s historical low of 0.02 borer per plant. Minor population increases from 2015 were documented in seven of the nine crop districts, except in the east-central and northeast regions. Larval densities in the central area rose to 0.24 borer per plant, or 24 per 100 plants, the highest average recorded in that area since 2007. Although more sites had economic averages above 1.0 larva per plant than in recent years, and second-generation larvae were detected in 49 of the 229 fields (21%) surveyed compared to14% in 2015, the very low state average of 0.11 borer per plant indicates that Bt corn continues to suppress corn borer populations and reduce the pest status of this insect in Wisconsin.
Soil Science Extension
University of Wisconsin Madison