In an attempt to curb further corn rootworm resistance to Bacillus thuringiensis (Bt) cornhybrids, the EPA has proposed new requirements for areas that are at risk to resistance. Its suggestions, however, may not be enough.
Last January, the EPA published its proposed framework to prevent corn rootworm resistance, acknowledging that the pest has already developed resistance to Bt corn in some areas of Iowa and Illinois. The agency suggests that areas that have a high risk of developing resistance, which it calls the “red zone,” be required to rotate crops; use corn varieties that contain more than one Bt protein; or implement other integrated pest management (IPM) strategies and stewardship practices for corn rootworm.
The EPA defines the red zone as Iowa, Illinois, Nebraska, western Indiana, southwestern Wisconsin, southern Minnesota and eastern South Dakota. Places outside of these areas can still be included in the red zone, particularly if corn-on-corn has been used for multiple years, there’s heavy use of Bt corn, corn rootworm infestations are regular and there’s spotty compliance with current refuge requirements.
The agency also recommended that 70% of corn acres in the red zone take part in IPM efforts, while 50% of corn acres outside of the red zone use IPM.
But Michael Gray doesn’t think this is enough. In the article, “U.S. EPA’s Proposal to Prevent Western Corn Rootworm Resistance: Does IPM Implementation Have a Realistic Chance?” the University of Illinois Extension entomologist asks, “Why not propose that some form of IPM be put in place on 100% of corn acres regardless of zone characterization?”
While he thinks that corn rotation is a viable pest management tactic for corn rootworm in many areas of the Corn Belt, he says the pest is resistant to two Bt proteins — Cry3Bb1 and mCry3A — in some locations, as well as rotation. Gray says crop rotation will remain a good strategy, even in these areas, but other tactics will need to be more fully integrated into a long-term corn rootworm management program.
One suggestion by the EPA he agrees with is banning the use of soil-applied insecticides with Bt hybrids. While Gray says these products do have their place in the fight against corn rootworms, especially when used with non-Bt hybrids, using them with Bt corn can have negative consequences.
“The authors of two recently published journal articles have confirmed that use of a planting-time soil insecticide with a rootworm Bt hybrid delays emergence and increases the chances of non-random mating; thereby, hastening the onset of resistance to Bt proteins,” he says. “When a planting-time soil insecticide is used with a pyramided Bt rootworm hybrid for the sole purpose of rootworm protection, it’s hard to find any convincing argument that this is a good IPM or resistance management approach.”
Following the review of comments, the EPA says it will finalize appropriate measures to address the issue of corn rootworm resistance to Bt corn.
What do you think about the current state of corn rootworm management practices and concerns about resistance to Bt hybrids? Post your comment at the bottom of this column and get the conversation going.