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Bacillus thuringiensis (Bt) Plant-Incorporated Protectants - page 11 / 30





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Bt Plant-Incorporated Protectants October 15, 2001 Biopesticides Registration Action Document

would develop to compare IRM strategies for Bt field corn. For example, if a high dose is achieved to control ECB (as it is for the currently registered Bt corn products), then these models predict that ECB will not evolve resistance for at least 99 years if a 20% refuge is implemented in the Corn Belt. Models are also used to predict the evolution of CEW resistance. These models indicate that 50% non-Bt field corn refuge in cotton-growing areas is sufficient to delay CEW resistance for at least the time frame of the registrations. A 20% non-Bt field corn refuge in the Corn Belt is sufficient to delay CEW resistance because CEW do not overwinter in the Corn Belt. EPA believes that the use of these models provides confidence that resistance will not evolve under the time frame of the registrations.

For Bt sweet corn, no specific refuge requirements are necessary because sweet corn is typically harvested much earlier than field corn, 18-21 days after silking, and before most lepidopteran larvae complete development. However, to mitigate the development of resistance, EPA has determined that crop residue destruction is necessary within 30 days. This practice will likely destroy any live larvae left in Bt sweet corn stalks and prevent overwintering of any resistant insects.

The IRM program for Bt field and sweet corn also require: 1) anyone purchasing Bt corn to sign a grower agreement which contractually binds the grower to comply with the IRM program and that there will be a mechanism by the year 2003 by which every grower affirms, annually, their contractual obligations to comply with the IRM program, 2) an IRM education program, 3) an IRM compliance monitoring program including a third party compliance survey and mechanisms to address non-compliance, 4) an insect resistance monitoring program for each target insect pest, 5) remedial action plans to be implemented if resistance does develop, and 6) annual reporting of the IRM (and other) activities. No other pesticide products than the Bt crop products have such extensive IRM requirements.

b. Bt Cotton

At this time, the Agency believes that available empirical data substantiate the success of the 5% external unsprayed, 20% external sprayed, and 5% embedded structured refuge options to delay resistance. However, EPA believes that it is imprudent to allow the 5% external, unsprayed refuge option for more than a limited period of time because current data indicates that this option has a significantly greater likelihood of insect resistance than either of the other refuge options. The 2000 SAP stated that the external, unsprayed option poses the highest risk to resistance evolution especially for cotton bollworm. Therefore, the external, unsprayed option expires after three growing seasons (September 30, 2004). During the next two years, the registrant is required to develop considerable new data on alternative host plants as possible effective refuges. In addition, the registrant is required to submit protocols by December 1, 2001, to begin field tests on alternative hosts and chemical insecticide sprays on Bt cotton, and to provide annual reports each January 31st. If any of these terms and conditions are not met, the external, unsprayed refuge option will be eliminated. If, based upon these, and any other pertinent data, the registrant requests an amendment to the registration extending the expiration date of the external, unsprayed option, EPA will conduct


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