Genetically Engineered Crops and Pesticide Use

When genetically engineered (GE) crops first came on the market in 1996, proponents claimed that they would need far less pesticide than conventional crops. Most genetically engineered crops are modified to either tolerate the herbicide glyphosate (HT crops) or to produce their own insecticide (Bt crops), so in theory, fewer applications of pesticide on GE fields would be sufficient to take care of pests. For the first three years of use, this was true. However, a new report by agricultural economist Dr. Charles Benbrook, Genetically Engineered Crops and Pesticide Use in the United States, shows that farmers now use more pesticide on the top three GE crops—corn, soybeans, and cotton—than on conventional varieties.

From 1996 to 1999, pest management in GE corn, soybeans, and cotton was relatively simple and effective, and engineered crops needed less pesticide than conventional varieties. By 2000, however, a contrary trend appeared—an increase in herbicide use on HT varieties over conventional varieties. That trend has continued and even accelerated in the last four years. Now, nine years of data on GE crops and pesticide use indicate that a total of 122 million more pounds of pesticides have been used on engineered crops than on conventional ones over that period.

According to the report, the difference in pesticide use is due to a sharp increase in herbicides applied to glyphosate-tolerant crops. This has occurred due to the emergence of new weeds—glyphosate-tolerant ones. As weed scientists have predicted for years, the widespread use of glyphosate on millions of acres of GE crops has selected for weeds that are tolerant to the chemical. These new weeds are subdued only by multiple applications of glyphosate and/or other herbicides.

Price drops for glyphosate and other herbicides and vigorous marketing by herbicide manufacturers have led farmers to apply more and more herbicides to deal with the new weed problem. Between 1996 and 2004, farmers used 138 million more pounds of herbicides on GE varieties than on conventional ones.

This huge increase was offset a bit by a welcome decline in insecticide use on Bt varieties. Between 1996 and 2004, 15.6 million fewer pounds of insecticide were used on Bt crops compared with conventional varieties.

The report predicts that the intensity of herbicide use on GE crops is not likely to subside in the near future because of the popularity of HT varieties, the limited supply of seeds for non-HT varieties, and increasingly aggressive herbicide company campaigns targeting farmers growing HT crops.

The Union of Concerned Scientists funded the analytical work on which the report is based.