Field data from the annual survey of adult corn rootworms in August revealed an increase from 2007 populations in 6 of the 9 agricultural reporting districts, including the southwest, southeast, west central, northwest, north central and northeast, and a decrease in populations in the remaining districts. The state average was 1.0 beetle per plant, the same average as in 2007. Average populations by district were as follows: northwest 1.1; north central 1.5; northeast 1.6; west central 1.0; central 0.5; east central 0.6; southwest 0.5; south central 0.9; southeast 0.6 (see table on Page 152). The western species constituted 52% of the state average population, while the northern species made up about 48%. Research entomologists consider an average of 0.75 beetle per plant to indicate an elevated risk for root injury in continuous corn the following year if some form of control is not used, and 38% of 229 fields in the major corn growing counties had such a count or higher. The obvious conclusion from these results is that there is a high potential for rootworm damage to continuous corn next season.
Soil Science Extension
University of Wisconsin Madison