Western Corn Rootworm Rebounds in Some Illinois Locations

By Mike Gray

As we entered this growing season, many questions remained regarding the fate of the western corn rootworm population throughout Illinois. The past two years, corn rootworm larval injury and adult numbers have been very low. Explanations included saturated soils during larval hatch (late May and early June), extensive use of Bt hybrids, and commonly applied broadcast treatments (to corn and soybean fields) of tank-mixed fungicides and insecticides.

The third week of June, Joe Spencer, an entomologist with the Illinois Natural History Survey, reported some significant root pruning on plants in plots just north of Urbana. On July 5, Mike Vose, with the Orr Research and Education Center in Perry, noted having observed more western corn rootworm beetles in the trap crop (late-planted corn) than he saw during the entire season last year.

On July 11, Ron Estes, senior research specialist in the Department of Crop Sciences, and our summer research crew began to evaluate plots near Urbana for corn rootworm injury. Ron described the feeding as more significant than last year, with injury on some check (control) roots significant--several nodes of roots pruned. He noted that root injury at the Orr and Monmouth Research and Education Centers may be low to moderate despite more adults in the trap crop. Nick Tinsley, a Ph.D. student and visiting research specialist in agriculture in the Department of Crop Sciences, photographed the western corn rootworm adults that had emerged into a 10- by-10-ft walk-in tent near Urbana over 3 days late last week (July 8-11). This level of emergence far exceeds that observed last year during a comparable sampling period for this experiment.

Western corn rootworm adults, 3-day emergence (July 8–11), from a single 10-by-10-ft walk-in tent near Urbana.

Over the next few weeks we will continue to dig, wash, and evaluate roots in our plots located near DeKalb, Monmouth, Perry, and Urbana. I'll share the preliminary rating results in later issues of the Bulletin. It is my hope that we can also conduct some western corn rootworm adult surveys around the state this summer and share those numbers during fall and winter University of Illinois Extension meetings. If you observe significant levels of root injury this summer, please share your observations with me.

Source: University of Illinois