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Issue No. 5, Article 1/May 7, 2010

"Refuge-in-the-Bag" Registration Approved by US EPA for Optimum AcreMax 1

On May 3, DuPont announced that the US Environmental Protection Agency (EPA) had approved the company's request for a seed mixture refuge for corn rootworms when planting Optimum Acre-Max 1 Pioneer corn hybrids (seed blend of 90% Herculex Xtra [Cry 1F + Cry34/35Ab1] and 10% Herculex I [Cry 1F]). The press release indicated that this new approach will be used in some producers' fields this year in preparation for the 2011 growing season. Farmers who elect to use Optimum Acre-Max 1 Pioneer corn hybrids will be able to reduce their corn rootworm refuge from the current structured 20% to a 10% seed mixture. According to the May 3 media alert, "In addition to the Optimum® AcreMax™ 1 product registration announced April 30, the EPA also has granted Pioneer registration for Optimum® AcreMax™ RW products, which integrate 90 percent Herculex® RW seed and 10 percent of a hybrid from the same genetic family without biotech insect protection. All seed in the bag is herbicide tolerant." Herculex RW corn hybrids express the Cry 34/35Ab1 binary proteins.

On April 30, the US EPA Office of Pesticide Programs, Biopesticides and Pollution Prevention Division, released a 33-page Biopesticides Registration Action Document titled Optimum®AcreMax™ B.t. Corn Seed Blends. A number of quotes from the document, which may shed some additional light on this significant development, follow.

  • "Given the potential benefits attendant to the blended refuge concept, EPA concludes that it is in the best interests of the public and the environment to issue the registrations for OAM 1 and OAM RW without delay for the 2010 growing season. The registration is only effective for the current growing season. Therefore, consistent with the Agency's policy for making certain registration actions more transparent, EPA is issuing these time-limited registrations with an initial period to expire September 30, 2010, and, concurrent with their issuance, providing a 30-day public comment period on the time-limited registrations" (p. 13).
  • "The data from these model simulations indicate comparative durability values of 11.3 years for the 10% blended refuge and 20.2 years for the 20% block refuge. Thus, the 10% blend was 45% less durable than the 20% block refuge currently required for single trait CRW PIPs" (p. 7).
  • "Based on our current assessment, we conclude that significant acreage of a 10% seed blend with a single, non-high dose mode of action such as Cry34/35Ab1 likely increases the risk of resistance for all B.t. corn products containing Cry34/35Ab1. But, the current time-limited registration will not likely increase the risk of resistance to Cry34/35Ab1" (p. 12).
  • "Pioneer projects that the time-limited registrations being granted for the 2010 growing season will result in planting on only approximately 0.042% of acres of non-Red Zone geography corn acres; and only on approximately 0.077% of Red Zone geography corn acres. In the context of 90 million acres of corn planted in the United States annually, we conclude that plantings on such limited acreage will not have effects on CRW resistance development" (p. 12).
  • "The Red Zone is defined by Pioneer as 90 counties that have a 100% chance of corn rootworm infestation in any given year. These counties are primarily located in northeastern Illinois, northwestern Indiana and, to a lesser extent, southeastern Wisconsin and southwestern Michigan. Because of the strong selection pressure present in the Red Zone, it is considered a potential area for corn rootworm resistance to develop" (p. 4).
  • 90 days from the date of registration: "Pioneer must provide the Agency with a copy of the grower agreement, associated stewardship documents, and written description of a system, which assures that growers will sign grower agreements and persons purchasing OAM1 corn will annually affirm that they are contractually bound to comply with requirements of the insect resistance management (IRM) program" (p. 15).
  • By December 1, 2010, for western corn rootworms and December 1, 2011, for northern corn rootworms: "Pioneer must implement an enhanced resistance monitoring plan for OAM1" (p. 15).
  • By December 1, 2010: "Pioneer must submit a detailed OAM1-specific resistance monitoring and remedial action plan, including an analysis to determine the expected field performance criteria for OAM1 products so that unexpected damage can be benchmarked" (p. 15).
  • "Because the refuge for corn rootworm is blended in each bag or box of OAM1 seed, no additional corn rootworm refuge is required. A refuge must be planted for corn borers. The refuge must be planted with corn hybrids that do not contain Bt technologies for the control of corn borers" (p. 16).
  • "External refuges must be planted within ½ mile. If perimeter or in-field strips are implemented, the strips must be at least 4 consecutive rows wide. The refuge can be protected from lepidopteran damage by use of non-Bt insecticides if the population of one or more of the target lepidopteran pests of OAM1 in the refuge exceeds economic thresholds" (p. 16).
  • "We expect OAM1 to have the following benefits: (1) Reduced pesticide use in the refuge. . . . (2) Significantly less complicated refuge deployment for the corn rootworm active ingredient. . . . (3) Increased grower compliance with IRM requirements for the corn rootworm active ingredient" (p. 9).
  • "In addition, indirect benefits of introducing Optimum® AcreMax™ 1 may include reduced energy consumption for manufacture, transport, and application of chemical insecticides; reduced waste streams arising from pesticide manufacture; reduced disposal of pesticide waste containers; and reduced residues from pesticide applications" (p. 10).

This registration opens up a new chapter in the implementation of resistance management strategies designed to delay or prevent resistance development to Bt corn hybrids. This development raises many additional questions:

  • Will Pioneer's registrations for OAM1 and OAM RW be extended to include growing seasons beyond 2010?
  • Will corn growers be sufficiently interested in this seed-blend approach to IRM if 10% of the seed must serve as a refuge? Our surveys of growers at the 2010 Corn and Soybean Classics indicated that if the refuge seed comprises 6% to 10% of a bag, interest in this approach fell below 60%. (See this article in issue 2 of the Bulletin for more details.)
  • Will the US EPA extend registrations to other companies that allow seed mixtures to form the core of their IRM plans for Bt hybrids?
  • Although producers who plant SmartStax hybrids in 2010 must implement a structured 5% refuge, will this requirement change to a seed- mixture IRM approach at the 5% level in subsequent growing seasons?
  • With the likely transition to seed mixtures as the IRM foundation for corn rootworms, how much longer will the agribusiness community sustain the discovery, development, and marketing costs associated with soil insecticides?
  • If corn rootworm resistance to Bt does develop at some point, what options will remain for growers to control this insect pest effectively? With crop rotation no longer an effective management option in many areas of the "Red Zone," we could have some significant challenges to confront if the soil insecticide market were to completely "dry up."

As I've indicated in earlier articles in the Bulletin, the early planting this season and favorable root establishment could help corn rootworm populations rebound from the past two seasons. Large root systems at the time of larval hatch (usually late May across central Illinois) could lower intraspecific competition for larval feeding sites and result in greater densities of western corn rootworms this year. I look forward to your reports this summer regarding how well corn rootworm products are performing.--Mike Gray

Author:
Mike Gray

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