Framework to Delay Corn Rootworm Resistance

In response to signs that the corn rootworm is becoming resistant to single trait Bt products, EPA is implementing new, more protective requirements designed to delay corn rootworm resistance to genetically engineered “Bt corn.” Bacillus thuringiensis (Bt) Corn produces a Bt pesticide, long used as part of organic farming, as part of the plant itself, to address corn rootworm pests.

These actions will ensure farmers will have safe, effective tools for years to come to control one of the most troublesome pests confronting the nation’s corn growers. Use of Plant Incorporated Protectants (PIPs), including Bt corn, is one of the safest methods of insect control.  If used properly, PIP crops greatly reduce the need for conventional pesticides and the risks those pesticides may pose to human health and the environment.  For these methods to continue to be available, it is essential that they remain effective.

Learn more about EPA’s framework to delay corn rootworm resistance:

What requirements are included in EPA’s framework to delay corn rootworm resistance?

EPA’s framework to delay corn rootworm resistance outlines specific actions to address issues related to potential corn rootworm resistance to Bt corn before more serious problems take root and includes corrective measures if resistance to Bt corn is confirmed. Integrated pest management, including crop rotation, proactive early warning efforts and effective communication across the affected agriculture community are all key facets of the new framework.

Specific measures include:

  • Companies supplying Bt corn will be required to implement an Integrated Pest Management (IPM) program for corn rootworm management and work with growers to help them use these practices.
  • IPM practices that are required by EPA to be part of that program are:
    • Rotation to an alternate non-corn rootworm host crop;
    • Planting of pyramided Bt corn;
    • Rotating to an alternate PIP, if available;
    • Planting of non-Bt corn rootworm protected corn with a soil-applied insecticide at planting (especially practical when following a year of crop rotation).
  • Bt corn companies are required to investigate reports of unexpected rootworm damage to Bt corn fields and to work with growers to implement IPM-based corn rootworm management options.  This approach replaces the previous annual monitoring strategy in which a few populations were sampled from random locations in the Corn Belt.
  • Unexpected damage investigations require the use of uniform damage-level triggers across the biotech industry to identify unexpected damage to fields in single and pyramided Bt corn.
  • Use of on-plant assays to confirm resistance in corn rootworm populations sampled from fields with unexpected damage.
  • If resistance is confirmed, the mitigation action area is defined as ½ a mile around the resistant site. Mitigation actions occur on the affected farm land only, and other affected growers in the area will be notified by the Bt corn company if they planted the same trait.

The Agency recommends that growers develop a multi-year management plan in consultation with Bt corn companies and/or extension entomologists, and/or crop consultants to use all IPM 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 PIP, if available, or planting non-corn rootworm corn with a soil-applied insecticide at planting.

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How do I know if I am in an area of corn rootworm resistance?

Resistance of corn rootworm to Bt corn has been documented in parts of Iowa, Nebraska, and Illinois. However, EPA believes that other parts of the Corn Belt, where corn rootworm infestations are common and the use of Bt corn is high, are also at risk for resistance. These areas are known as the corn rootworm "red zone" and include portions of Iowa, Illinois, Nebraska, western Indiana, southwestern Wisconsin, southern Minnesota, and eastern South Dakota. Other corn-growing regions outside of these states may also be at risk for resistance, though not to the same extent as areas in the "red zone." The Department of Agriculture for each state may have additional information on specific areas of corn rootworm resistance.

Regardless of geography, if these conditions are prevalent on your farm or in your area, you are likely part of the “red zone”:

  • Corn-on-corn for multiple years
  • Heavy use of Bt corn
  • Use of the same Bt trait year after year
  • Regular corn rootworm infestations
  • Spotty compliance with current refuge requirements

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How does the new framework affect corn farmers?

The new framework should help extend the life of Bt corn products for U.S. corn farmers. The agreement is, however, between the companies selling and/or producing Bt corn and the EPA, and any requirements apply to the Bt corn companies themselves. These companies have agreed to promote increased IPM participation among growers who plant Bt corn to control corn rootworm. Company grower guides and representatives will help to educate growers by emphasizing the benefits of a diverse corn rootworm management plan and how best to control corn rootworm populations under various situations.

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How will the framework help reduce the likelihood of rootworm resistance?

The new framework relies on several proactive steps with Bt corn planting and/or quick actions put in place in case of Bt field failure. These steps can help reduce the occurrences of unexpected damage and reduce the spread of possible resistance. The following are examples of proactive steps to reduce the spread of possible corn rootworm resistance in Bt corn:

  • Growers scout, detect, and report unexpected damage to Bt corn companies early;
  • Bt corn companies work with growers to respond in the most effective manner to resolve field failures before the upcoming growing season;
  • Implement IPM best management practices.

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What happens if, or when, rootworm resistance does develop?

The framework places great emphasis on scouting for unexpected Bt damage in corn fields to proactively identify potential corn rootworm problem populations. In the event of field damage, the grower should contact the company that supplied the Bt corn.

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.  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.

Bt corn companies must also notify extension scientists, crop consultants, other local advisors, and nearby farmers who use the same trait.  As resources permit, EPA is looking to develop options to make this information public, such as lists of states with confirmed corn rootworm resistance and associated Bt traits. This would allow growers to obtain information about best management practices in their areas before buying seed for the following corn growing season. 

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