Resistance Management Update for Bt-Corn

March 22, 1999

Many of you probably are aware that the National Corn Growers Association (NCGA) and companies registering and selling most of the Bt-corn hybrids reached an agreement-in-principle this past January; the agreement takes effect in the year 2000. The key elements of the agreement regarding insect resistance management strategies are as follows:




  • A single protective and practical corn refuge requirement for the primary corn-growing region (20%) and a single corn refuge requirement for the primary cotton-growing region (50%)

  • A clear and consistent insect resistance management grower agreement

  • Effective grower education programs

  • Appropriate surveys to track grower adoption

  • Continued monitoring for insect susceptibility to Bt


The objective of the agreement was to present a consistent, unified message about resistance management so that growers can implement practical strategies to preserve the technology.


In general, university and USDA entomologists applaud the agreement. However, some differences in recommendations about percentage non-Bt-corn refuge still exist among university and industry scientists. The North Central Regional Research Committee on Ecology and Management of European Corn Borer and Other Stalk-Boring Lepidoptera (the NC-205 Committee) recommends that if a grower wants to treat a non-Bt-corn refuge with conventional insecticides to control corn borers, the refuge must comprise 40% of his or her corn acres. However, neither industry scientists nor the NCGA has indicated that a non-Bt-corn refuge needs to comprise more than 20% of the corn acres. Therefore, a discrepancy still exists. When more information about size and configuration of non-Bt-corn refuges is generated, we will provide the information and offer our insight. In the meantime, we strongly encourage growers who plant Bt-corn to plant a non-Bt-corn refuge, minimum of 25%, treated or not. Implementation of resistance management strategies is essential for preservation of this excellent tool for managing corn borers.–KS



Author: Kevin Steffey