EPA designated “red zone” is at risk for developing Bt resistant populations of corn rootworm.
EPA designated “red zone” is at risk for developing Bt resistant populations of corn rootworm.

Corn rootworm, corn earworm and corn borers all want a bite of the golden crop for which they’re named, and you’ll pay the price if they’re resistant to Bt traits. In 2016, 76% of corn planted in the U.S. used Bt technology. With more use, more insects could develop Bt resistance.

Manage crops now to delay resistance as much as possible. You can’t rely on the industry to constantly replace Bt options because new products take 10 to 15 years to develop. 

With Bt corn planted across the country, the insects that survive are more likely to carry genes that make them less susceptible to Bt proteins, says Sean Evans, Monsanto technology development manager. As those individuals mate with each other, they’re more likely to pass resistant genes to the next generation. This is why Bt refuge is so important. Refuge plants do not contain Bt traits, therefore susceptible insects survive and can continue to pass susceptibility onto offspring, he adds.

Start by identifying potential resistance. Scout your Bt fields and your non-Bt fields, says Ric Bessin, Extension professor at the University of Kentucky. A watchful eye will tell you if insects are breaking through.

However, heavy insect feeding isn’t always caused by Bt trait failure. Make sure you’re not looking at refuge corn, and review records to make sure you’re in a field planted with Bt crops. Damage could also be caused by insect species not controlled by Bt traits, such as stink bugs. Wind blowing over cornstalks could mimic the effects of corn rootworm, too. 

“There are a number of things that can appear like resistance that are not resistance,” Bessin says. “But it’s still very important for growers to go out and monitor for it because if resistance is a possibility, we need to look at it very carefully.”

Report potential Bt resistance to your seed reps. After you contact your rep, they will visit your field to check plant damage and potential causes, says Clint Pilcher, DuPont Pioneer strategy lead for insect resistance management. If the damage meets the required thresholds and there are no other possible explanations, the company will collect a sample of insects from the field.

At that point, it’s too early to tell much, Pilcher says. Still, you should assume the pests are resistant and take action.

Adopt resistance management tactics. There is no one-size-fits-all approach, says Duane Martin, Syngenta commercial traits product lead. Follow an integrated pest management program.

For instance, growing continuous corn while using the same trait technology increases selection pressure for resistant insects. Crop rotation effectively eliminates those survivors.

If you plant a nonhost crop such as soybeans, surviving resistant insects will die out. “That’s one way to reset the population,” Evans says.

Work with your input suppliers or crop consultant to devise a multiyear management plan to mitigate pest pressure. If crop rotation isn’t possible, Pilcher recommends alternating pest control practices, such as switching from a single to a pyramid trait product, rotating to a product that uses a different Bt protein or planting non-Bt corn with an insecticide. 

“Our goal is to integrate our pest  management practices and tactics so we can delay the onset of resistance for as long as possible, but that doesn’t mean it’s not going to happen,” Pilcher says. “And when it does, it doesn’t necessarily mean the sky is falling. We’re fortunate with pests like corn rootworm that there are other tools in the toolbox to help manage this significant corn pest.”