By now, you’ve heard that western corn rootworms in a few Iowa cornfields have overcome the Bt toxin Cry3Bb1.

One thing that all the fields had in common: continuous use of corn with the Cry3Bb1 protein “for at least three and as many as six consecutive years,” says Aaron Gassmann, the Iowa State University entomologist who documented the resistance. “This indicates the need for better integrated pest control, and not relying on a single Bt corn year after year.”

To prevent widespread rootworm resistance to Bt, growers must adopt “a long-term integrated management approach that includes multiple tactics,” says Mike Gray, a University of Illinois entomologist who has documented severe root damage and lodging of Bt hybrids in Henry, LaSalle, and Whiteside counties. You should:

Comply with refuge requirements. “There are a lot of different refuge scenarios for 2012, so it’s very important to be knowledgeable about the hybrids you are planting and their refuge requirements,” Gray says.

•Rotate to soybeans or another non-host crop.Crop rotation is the best way to reduces rootworm density, Gray says.

•Diversify modes of action. Switch to a hybrid containing a different Bt toxin, Gray says. Or choose a “pyramided” hybrid that expresses more than one Bt toxin targeting corn rootworms.

•Apply conventional insecticidesin fields with known high rootworm pressure. Choices include liquid or granular insecticide applied at planting or egg-laying suppression programs.

However, this does not mean that using “a Bt corn rootworm hybrid plus a soil insecticide should be a standard and routine practice in a single growing season,” Gray emphasizes. Nor should growers routinely plant a Bt corn rootworm hybrid in fields that were sprayed for western corn rootworm adults the previous summer, he says.

“We need to avoid throwing everything, including the kitchen sink, at western corn rootworms in a single growing season,” Gray says. Not only is this “insurance” approach expensive, “but ultimately it may select for resistance more rapidly and lead to unwanted environmental consequences.”

•Monitor root damageand beetle numbers. “I encourage growers to walk fields a time or two during the season to look for unexpected damage,” says Michigan State University Entomologist Chris DiFonzo. If you see significant root pruning or a large number of adult beetles in Bt corn, “contact someone as soon as possible, rather than mentioning it after harvest. This will alert companies and universities to potential problems early enough to take samples.”