Resistance to Bt corn prompts new EPA requirements

By Stephen Davies

© Copyright Agri-Pulse Communications, Inc.



WASHINGTON, Feb. 18, 2016 - The Environmental Protection Agency is imposing new requirements on biotech seed companies to ensure that farmers use a variety of practices, including crop rotation, to guard against rootworm resistance to Bt corn. 

EPA also is setting new requirements for identifying and managing resistance problems. 

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The agency cited signs that the corn rootworm is becoming resistant to single-trait Bt products. EPA released the requirements Thursday after considering public comments for about 10 months.

The agency's new “framework” for managing root worm resistance calls for growers to “develop a multi-year management plan in consultation with Bt corn companies and/or extension entomologists, and/or crop consultants to use all IPM (integrated pest management) tools in rotation to reduce the frequency of unexpected damage and resistance occurrences in Bt corn.”

“The preferred strategies, in descending order, are crop rotations, use of pyramided Bt corn, rotating to an alternate Plant Incorporated Protectant (PIP), if available, or planting non-corn rootworm corn with a soil-applied insecticide at planting.”

“Proactive IPM, including the rotation of fields to non-Bt corn crops every few years and other changes will greatly reduce resistant corn rootworm populations,” EPA said.

“Pyramided” refers to corn with more than one Bt trait.

Companies also will be required to investigate reports of damage and notify any other affected companies, neighbors, extension specialists, and crop consultants in areas where populations are found to be resistant, EPA said. 

“In the event that the problem populations are determined to be resistant, these companies are required to work with growers whose fields have resistant populations to implement a mitigation plan,” EPA said. 

“The fields that fall into the mitigation action area must be proactively treated against corn rootworm with the most effective tools available, including the following: crop rotation to soybean or another non-host crop, increasing refuge sizes for pyramided products containing the compromised trait, or planting different PIP traits. The goal is to reduce the level of resistance in the mitigation action area and to limit the spread of resistance to neighboring fields.”

Nathan Fields, director of biotechnology and economic analysis for the National Corn Growers Association, said the requirements are “workable” from the growers' standpoint. “There will be some growing pains possible here and there,” Fields said. 

The agency requirements should result in “more outreach by seed dealers and seed companies” to farmers to ensure they are managing for resistance and in “making sure high pressure areas get reported,” Fields said. 

The requirements clarify which best management practices should be used, Fields said.

EPA first announced plans in the fall of 2014 to expand its requirements for managing rootworm resistance. 

The best management practices “cannot all be implemented in the same year at the same time. … The technology provider and grower have to agree on using one or two of those over a couple-year period to manage a hard-to-control or resistant population.” 

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