Key findings: GM and pesticides report
Impacts of Genetically Engineered Crops on Pesticide Use: The First Thirteen Years
by Charles Benbrook
Accessing the report
The full report - pdf (3.68 MBs, 69 pages)
Executive Summary - pdf (1.44 MBs, 15 pages)
Supplemental Tables - pdf
Major Findings and Conclusions
HT [GM Herbicide Tolerant] corn reduced herbicide use in its ï¬rst year of introduction by almost 0.8 pounds per acre. Over time, increases in the average rate of application of glyphosate [active ingredient in Roundup, the herbicide applied to Roundup Ready - RR - crops] drove herbicide use upward on HT acres.
By 2005, herbicide use on conventional and HT corn acres was essentially identical and by 2006, the average pounds applied on an HT corn acre had risen to 0.08 pounds above the average pounds of herbicides applied to an acre of corn planted to a conventional variety.
The same pattern is evident with HT cotton. Each acre of HT cotton in 1996 reduced herbicide use by three-quarters of a pound, but by 2001, rising glyphosate use on HT acres had overtaken the average pounds applied on conventional acres.
Today, each acre of HT cotton increases the average pounds of herbicides applied by about two-thirds relative to conventional cotton. RR soybeans reduced average herbicide use by 0.3 pounds per acre planted in 1996. Just two years later, USDA data show that average herbicide use on HT soybean acres had already risen above the average rate on acres planted to conventional soybeans. By 2008, the diï¬€erence had increased to 1.16 pounds per acre.
This dramatic change in herbicide application rates is unmistakable in USDA surveys of pesticide use on soybean farms. There is also general agreement on why the performance of RR soybeans has changed so dramatically over the years intense selection pressure from excessive reliance on glyphosate has triggered weed shifts to species more tolerant of glyphosate, as well as evolution of glyphosate-resistant biotypes.
As is the case with corn and cotton, steady reductions over the 13 year period in average soybean herbicide application rates per acre also contributed to the growing margin of diï¬€erence in overall herbicides applications on RR versus conventional crop acres. These reductions were brought about by the registration and growing market penetration of several low-dose herbicide products.
Over the ï¬rst 13 years of commercial planting of major GM crops in the United States, this analysis shows that:
”¢ GM crops increased overall pesticide use by 318.4 million pounds, or by 7.5% of combined use on the three crops;
”¢ Herbicide tolerant crops increased herbicide use by 382.6 million pounds, while Bt crops reduced insecticide use by 64.2 million pounds;
”¢ Herbicide tolerant soybeans accounted for 92% of the increased herbicide use across the three HT crops;
”¢ GM crops reduced pesticide use in the ï¬rst three years of commercial introduction by 1.1%, 2.3%, and 2.3% per year, but rising rates per crop year of glyphosate on RR varieties increased aggregate pesticide use across all GM traits and acres beginning in 1999;
”¢ Rates of corn and soybean herbicide and corn insecticide applications on cropland planted to conventional varieties trended downward during the study period by 24% to over 90% as a result of the shift toward lower-dose pesticides;
”¢ The 26% increase in the pounds of pesticides applied on GM crops in 2008, compared to acres planted to conventional varieties, was almost ï¬ve-fold greater than the 5.8% increase just ï¬ve years earlier, in 2003; and
”¢ The upward trend in pesticide use on GM crops has been driven almost solely by the rapid emergence and spread of weeds tolerant of or resistant to glyphosate. Moreover, further increases in overall pesticide use on GM crops is inevitable in 2010 and for the foreseeable future in the U.S. because of the further emergence and steady spread of weeds resistant to glyphosate.