To date, data from South Dakota indicates that Bt-corn fields are showing unexpected corn rootworm damage in the vicinity of Lake Campbell, Bruce, Milbank, Baltic, and Colman, reports Ada Szczepaniec, Assistant Professor and SDSU Extension Entomologist in a recent iGrow.org article.

"It should be noted that not all problem fields are reported; therefore, it is difficult to quantify whether these are isolated instances or represent a potential broader scale occurrence," Szczepaniec said. "In those fields that have been investigated, resistance to Bt hybrids has not been confirmed yet, and we will work to collect data to test this next year."

She adds that fields with a history of at least three years of continuous corn with the same Bt hybrid are at the greatest risk of having Bt-resistant populations of corn rootworms.

"Corn rootworm issues in fields planted with Bt-corn hybrids have been getting a fair amount of attention in the Midwest and Northern Plains. Because South Dakota has a substantial diversity of soil types and growing conditions, it is likely that the severity of corn rootworm issues varies significantly within the state," she said.

Szczepaniec is collecting data from South Dakota corn growers and will issue the results soon.