The Truth About Corn Rootworm Resistance

CORN ILLUSTRATED: No need to panic, no matter where you live.

Published on: Jul 23, 2013

A recent NPR report that aired has stirred up some consternation again about rootworm resistance issues. The report focuses on a case of control failure of rootworm larvae in transgenic corn in Nebraska.

Suddenly people fear the "tomato that ate Chicago" is true.

Not so, says Christian Krupke, a Purdue University Extension entomology. He keeps in close touch with Extension specialists in states where the lack of control has appeared, including Aaron Gassman, an Iowa State University researcher who published some of the first reports about control failure.

There is still some mincing in the industry about whether it is true resistance or not, but for all practical purposes, most researchers believe it is, Krupke says. The resistance is to the CryBb1 trait, the first trait marketed for rootworm control, dating back to 2003.

Stop resistance: You can keep rootworm larvae away from your part of the world if you follow recommendations that lessen the odds of insect resistance. This is a young rootworm larva.
Stop resistance: You can keep rootworm larvae away from your part of the world if you follow recommendations that lessen the odds of insect resistance. This is a young rootworm larva.

For areas where the resistance has been documented, the good news is that it doesn't seem to be spreading in a pattern, such as fanning out from a focal point like many infestations do. Instead it pops up in various locations. Early in all cases, affected fields have been in continuous corn with the same trait planted every year.

In states which haven't seen it yet, like Indiana and Ohio, Krupke doesn't see it as an impending threat, largely because it isn't moving out from a focal point.

The single best method of rootworm control if a resistance issue does develop anywhere is rotation to soybeans, Krupke says. The larvae can't survive on soybeans, as long as there is no volunteer Bt corn in the field, Krupke says. If there is volunteer corn, it needs to be controlled to prevent any rootworm survival issues.

It's also important to follow refuge requirements, and to consider switching up rootworm control technologies over time, including opting for a granular insecticide in the rotation, Krupke adds.