Respect rootworm — stay alert!

The question posed to the panel from the Indiana Certified Crop Advisers Association says it all. There’s talk about breakthroughs in control of corn rootworm to one specific genetic trait: the Cry3Bb1 event. The reports are from Iowa, Illinois, Minnesota and South Dakota. What does it mean for Indiana?

Key Points

Rootworm control problems with one genetic event noted in Western states.

Crop rotation still a good tool to prevent development of rootworm resistance.

Rotate crops, technologies and control measures; monitor your cornfields.


Question: I heard so much talk about the corn rootworm problems at winter meetings that I’m confused. I’m planting corn into soybeans and usually rely on genetic control. Should I do anything different this year?

Dan Ritter, Purdue University Extension ag educator, Newton County: “Resistance” has been confirmed in Iowa, Minnesota, South Dakota and possibly Illinois. Will this occur in Indiana? If we don’t take some precautions, possibly. One fact in our favor is that corn rootworm numbers are low in many areas of the state.

My corner of the state (northwest) tends to have the heaviest infestations. If we have lower populations, the chance of resistance and/or damage tends to be lower. To preserve this technology follow the three R’s: rotate crops, rotate technologies and rotate control measures.

Follow a good crop-rotation system if at all feasible. There are technology choices, so consider alternating what you use. Finally, the option of seed treatment and granular insecticides still exists. Stay on course this year, observe your refuge requirements, monitor your fields and rotate.

Andy Like, agronomist, Daylight Farm Service, Daylight: The most important measure would be to continue with the corn/soybean rotation. Secondly, rotate the rootworm trait you use. Considering your own corn/soybean rotation, the rootworm population would only be exposed to the same trait every four years.

If you’re in an area that doesn’t have heavy rootworm pressure, you may consider forgoing rootworm-traited corn, and use a soil or seed-applied insecticide for control to avoid developing resistance (to rootworms.)

Terminology of rootworm issue still unclear

The incidences of lack of control of corn rootworm in fields protected by a single, specific trait that has occurred in western states piqued enough interest for the committee planning the recent Indiana Certified Crop Advisers Conference to invite Ken Ostlie to come from the University of Minnesota and speak about the topic.

John Obermeyer, a Purdue University entomologist, notes that the rationale was that while it’s not yet been observed in Indiana, it’s an issue across the industry. Everyone should be aware of it, including CCA agronomists and farmers.

Ostlie has not only visited fields where rootworm control failed, but has conducted trials trying to pinpoint the specifics of what’s causing the failure. While his team has found some answers, there are still questions.

For example, the reported cases, although called resistance, have not technically met the definition of resistance set out by the U.S. Environmental Protection Agency. Is it, in fact, true resistance to the trait?

Second, will the problem move east? Is it possible that the western rootworm variant that lays eggs in first-year soybeans may react differently than western corn rootworms without that ability? These are questions researchers will try to answer.


This article published in the March, 2012 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.