Evaluation of Insecticides in Runoff from BT and non-Bt Cotton Fields

Abstract

Runoff samples were collected and analyzed from Bt (Bacillus thuringiensis) cotton and non-Btcotton fields for insecticides from 1996 through 1999. The insecticide analyses included pyrethroidand organophosphate insecticides based on the popularity and use throughout the Mississippi Delta incotton-producing areas. The purpose of this paper was to present and compare the insecticideconcentration data for runoff samples from the Bt-cotton fields to that from non-Bt cotton fields within theMississippi Delta Management Systems Evaluation project. The use of the genetically engineered Btcotton plant to produce its own pesticide reduced the volume of pyrethroid insecticides sprayed into theenvironment at the Beasley Lake Watershed in Mississippi. The reduced application dates and pyrethroidtypes on the Bt cotton sites as compared to the multiple applications of mutiple pyrethroid insecticides onthe non-Bt cotton sites to control the tobacco budworm and bollworm resulted in some reduction ofpesticides released into the environment. Even though the non-Bt cotton sites resulted in little to nodetects of the pyrethroid insecticides, the Bt cotton site had even lower concentrations in the runoff.Insignificant detects were found with the organophosphate insecticides for boll weevil control from eitherBt or non-Bt cotton sites. No detrimental environmental effect from the pyrethroid and organophosphateinsecticides was found from water samples of runoff from all tested sites within the watersheds of thisstudy.