These three corn plants show varying levels of rootworm control. (Photo by Carrie Muehling/WJBC)

By Carrie Muehling

BLOOMINGTON – Corn rootworm control continues to be a challenge in parts of Illinois, especially where farmers are growing corn year after year.

The weather didn’t give any natural control for rootworm populations during the 2012 growing season. Farmers saw very high rootworm populations, especially in fields with continuous corn cropping system where the same technology or no technology has been used over the past several years. And while 95 percent of the time the traits evaluated performed very well, there were instances where they did not.

“There are instances where we don’t see efficacy of the trait like we would like to see, and we see excessive feeding on the roots. In those instances, we’re trying to work with growers to be able to identify management strategies or use of other technologies that are going to help them be successful,” said Sean Evans, technical development representative for insect management with Monsanto.

Evans said farmers can expect varying degrees of performance based on the weather, but he is also concerned about resistance.

“We’re applying a technology that if we rely too heavily on is relatively weak against the pest in terms of the dosage of that toxin that the plant produces is not very high. We know that some insect survive the technology. So in our continuous corn cropping systems, populations are going to continue to build. Ultimately, they can overwhelm any technology that’s in the field, especially if it’s a single trait technology,” said Evans.

Any single trait technology can fail under very heavy pressure, especially when coupled with repeated use over the long term. Evans said he would expect a trait under heavy pressure that is utilized for many years to eventually decline in performance.While he is fairly confident the resistance is not wide spread, he knows it has developed in some localized pockets. He works with farmers to implement best management practices on those fields and monitor those fields very closely. Often he recommends a multiple strategy approach.

“We work very closely with those growers that are ‘in peril,’ I like to call it,” said Evans. “They have an issue, they want to correct it. We spend a lot of time, especially in my role, working one on one with those growers.”

Educational workshops and meetings throughout the winter have carried this message. Evans encourages growers to become more in tune with fields and detect any problem early. Scouting will be important and rotation may be necessary. Options include incorporating dual modes of action through stacked traits or using a single trait with insecticide. Evans said new efforts are being put forward and new technologies are still possible.

“The bottom line is that technologies aren’t going to come out quick enough to be able to keep up with a pace of development of resistance if we keep doing the same things we’re doing now, and growers need to understand that,” said Evans. “Likely we’ve got to protect the traits that we have there now, the technology, to increase the durability until we can get to these new release points.”

Carrie Muehling can be reached at carrie@wjbc.com.