This year's resistance management regulations regarding Bt corn will not result in many changes for Nebraska producers who grow the crop, a University of Nebraska (NU) entomologist says.

"In practical terms, things will remain the same for 2002, although resistance management compliance requirements have been strengthened," says Tom Hunt, an entomologist at NU's Haskell Agricultural Lab near Concord, NE.

The resistance management requirements for Bt corn as stated by the U.S. Environmental Protection Agency for 2002 are:

  • Growers must plant a refuge of at least 20% non-Bt corn that may be treated with insecticides as needed to control caterpillars, such as European corn borers, and other pests.
  • Refuge planting options include separate fields, blocks within fields and strips across fields.
  • External refuges must be planted within one-half mile of the Bt field; one-quarter mile or closer is preferred.
  • When planting the refuge in strips across the field, strips should be at least four and preferably six rows wide.
  • Insecticide treatments to control European corn borer, corn earworm, southwestern corn borer, fall armyworm and black cutworm in refuges are allowed only if an infestation reaches economic thresholds for these pests. Economic thresholds are determined using methods recommended by local or regional professionals. Microbial Bt insecticides must not be applied to non-Bt corn refuges.

"The EPA has clarified the language with respect to placement non-Bt refuges and relaxed a bit on row-width requirements for refuges planted as strips through a field," Hunt says.

Companies marketing Bt corn must monitor for the potential development of insect resistance, provide annual reports on the efficacy of resistance management plans and implement remedial action plans in the event insect resistance is detected.

"Many companies that market Bt corn have been performing these compliance activities for the last few years," the Institute of Agriculture and Natural Resources specialist says. "For Nebraska farmers, all this really means is that they may see some new language regarding resistance management in their contracts."

These changes follow a two-year-long EPA review. The EPA determined that Bt corn is safe and will be registered for another seven years.

"The EPA has done an extensive scientific evaluation and review of reports on Bt corn for controlling European corn borer and other related insects," Hunt says. "Some studies considered during the review addressed potential risks to Monarch butterflies, effects on birds and human allergies to Bt. They determined that Bt corn poses no significant risk to environmental or human health."