Many Questions Remain About Corn Rootworm Control Breakdowns

Minnesota entomologist lays out industry challenges.

Published on: Jan 6, 2012

John Obermeyer and others in charge of selecting speakers for the Indiana Certified Crop Advisor conference in Indianapolis decided that while the breakdown in control of corn rootworm by one specific genetic trait wasn't an issue in Indiana, it was raising enough questions and issues industry-wide that they should address it. "It's not a problem here now," says Obermeyer, Purdue University Extension entomologist, "But the issues are relevant to other issues related to traits. We wanted to bring everyone up to date on what was occurring in some western and northern states."

The most celebrated outbreak has been in Iowa, Where an Iowa State researcher has documented failure of a certain genetic event to control corn rootworm larvae over the past few seasons. The same problem has now been identified in parts of Illinois, Minnesota, Nebraska and perhaps one corner of Wisconsin.

Ken Ostlie from the University of Minnesota has seen the problem in farmer fields, and even conducted trials to try to help determine exactly what was happening. He made several important points during the conference.

First, technically, according to EPA language, the manufactures can make a case that technically, at least, resistance has not been proven. He notes, however, that it's obvious to experts that the break in control falls somewhere on the tolerant to resistant scale on the part of the insect.

Second, so far the problem is limited to western corn rootworms. Ostlie is holding his breath that it doesn't show up in northern corn rootworms, which would be a problem in his area. The species that affects Indiana fields is the western corn rootworm.

To be more specific, so far it has shown up in western corn rootworms which don't display the variant trait that allows them to lay eggs in soybeans fields, resulting in corn rootworm problems in first year corn. Until that developed in the 1990s, crop rotation was a fairly surefire way of preventing rootworm problems. Just because it hasn't been documented in the soybean variant yet doesn't mean it won't happen, but it's something to watch closely.

Third, where farmers have seen the [problem in the states where it has occurred, they need to take action to avoid the problem, Ostlie says. It has typically been most prevalent ion continuous corn fields where continuous exposure to the same genetics has occurred year after year. One option is rotation to soybeans, although that may n to work for everyone.

Another option is to switch to an event that still controls the rootworm, such as SmartStax. However, if you do that, he notes, you basically are back to one mode of action, that coming from the Herculex portion, if the other portion isn't providing control. The other option is to stay begin applying soil insecticides once again.