Planting Patterns of In-Field Refuges Observed for Bt Maize in Minnesota

The U.S. Environmental Protection Agency (USEPA) requires the use of nontransgenic refuges to slow the evolution of insect resistance to transgenic crops. In-field refuges, or refuges that are planted within the same field as the transgenic crop, are allowed; however, these refuges are required to be at least four rows wide. We described in-field planting patterns used by growers for both Cry1Ab [against Ostrinia nubilalis (Hubner)] and Cry3Bb (against Diabrotica virgifera virgifera LeConte) maize, Zea mays L. Maize fields known to contain Cry1Ab, Cry3Bb, or both were sampled in southwestern Minnesota during late June and early September 2005. Rows were sampled to describe the pattern of in-field refuges in the entire field. Most in-field refuges contained >20% Cry(-) seed (79% of Cry1Ab and 84% of Cry3Bb). However, only 5% of Cry1Ab fields and 2% of Cry3Bb fields with in-field refuges were in compliance with USEPA requirements because the Cry(-) seed was not in wide enough strips or blocks. Most growers had planted their fields with either finely mixed refuges or with strips that were too narrow. There was a high diversity in planting patterns, and the occurrence of Cry(-) seed was in random rows. Growers may have been rushed while planting and not noticed which seed was going into which rows. Resistance failures have not been documented for either O. nubilalis or D. virgifera virgifera, so better education programs will need to be undertaken to encourage growers to plant in-field refuges properly.