Insecticides Reduced in Runoff from Bt Cotton

Runoff water from Mississippi fields planted with genetically engineered cotton was virtually free of insecticides during a four-year Agricultural Research Service study.

To measure pesticide runoff, the scientists planted cotton that was genetically engineered to contain a toxin from the bacterium Bacillus thuringiensis. Researchers planted the Bt cotton near Beasley Lake in Sunflower County--one of three watersheds within ARS’ Mississippi Delta Management Systems Evaluation Area project. Because Bt cotton produces its own insect-inhibiting toxin, less pyrethroid insecticide is needed to control budworm and bollworm infestations.

From 1996 through 1999, agricultural engineer Robert F. Cullum and chemist Sammie Smith with ARS’ National Sedimentation Laboratory, Oxford, Miss., analyzed runoff samples for insecticides from both Bt cotton and non-Bt cotton fields. They looked especially for pyrethroids and organophosphates because of their widespread use throughout the 7,000-square-mile, cotton-producing area.

The fewer pyrethroid applications needed on Bt cotton sites reduced the amount of pesticides released into the environment. And while runoff from non-Bt cotton sites contained very slight amounts of pyrethroid insecticides, runoff fromBtcotton sites had almost none at all.

The team found only insignificant amounts of organophosphate insecticides used to control boll weevils in runoff from either the Bt or non-Bt cotton sites. The scientists concluded that there are no detrimental environmental effects from either pyrethroid or organophosphate insecticides in runoff from any of the watershed sites sampled during this study. The finding will be useful to extension workers, action agencies involved in water-quality planning, and farmers interested in reducing insecticide applications while maintaining control of pest infestations in their cotton crop.

ARS is the chief scientific research agency in the U.S. Department of Agriculture.

Scientific contact: Robert F. Cullum, Water Quality and Ecological Processes Research Unit, ARS National Sedimentation Laboratory, Oxford, Miss, phone (601) 232-2976, fax (601) 232-2915, cullum@sedlab.olemiss.edu.