More incidences of severe corn rootworm injury to Bt corn have been observed in northwestern and north central Illinois, said University of Illinois Extension entomologist Mike Gray.

Gray said the affected fields share some common features — corn has been grown without rotation and the Bt hybrids used have expressed the Cry3Bb1 protein for many successive years.

Gray answered a few questions to help producers make informed decisions before selecting 2012 seed.

How widespread is corn rootworm injury to Bt corn that expresses the Cry3Bb1 protein?

Producers who are unhappy with the level of root protection afforded by these corn rootworm Bt hybrids should contact their industry representatives.

As more information is generated, a more accurate assessment of this situation can be made, Gray said.

At this point, he doesn’t believe these fields represent a “needle-in-the-haystack,” nor does he believe control failures of Bt rootworm hybrids that express the Cry3Bb1 protein occur in most fields.

He encourages registrants to share the extent of these control failures with the broader agricultural and regulatory community. By taking this approach, producers will be able to make more informed choices regarding Bt corn rootworm products for the 2012 growing season.

Do these reports of severe corn rootworm pruning to Bt corn (Cry3Bb1) mean that resistance has been confirmed in these fields?

No. Confirmation of resistance requires collection of adults from affected fields and conducting further detailed laboratory investigations. Gray said growers should be careful not to make the leap that fields with severe rootworm injury are supporting a resistant western corn rootworm population.

Prior to this season, has significant root pruning been observed on Bt corn (Cry3Bb1)?

Yes. Gray said they have observed significant pruning on Bt corn (Cry3Bb1) in U of I corn rootworm efficacy trials soon after these Bt hybrids were commercialized.