A new study has found that widespread adoption of genetically modified crops has increased the use of weed-killing herbicides as weeds become more resistant, while decreasing the use of insecticides.
University of Virginia economist Federico Ciliberto led the largest study of genetically modified crops and pesticide use to date, alongside Edward D. Perry of Kansas State University, David A. Hennessy of Michigan State University and GianCarlo Moschini of Iowa State University. The four economists studied annual data from more than 5,000 soybean and 5,000 maize farmers in the U.S. from 1998 to 2011, far exceeding previous studies that have been limited to one or two years of data.
“The fact that we have 14 years of farm-level data from farmers all over the U.S. makes this study very special,” Ciliberto said.
Farmers who grew GM soybeans used 28 percent more herbicides than farmers who grew non-GMO soybeans. Ciliberto attributes this increase to the proliferation of glyphosate-resistant weeds.
Charles Benbrook, who has published several papers on the use of glyphosate herbicide, says the amount of herbicides used in more recent years is likely much higher. “Their analysis stops at 2011, around the time herbicide use took off in response to the spread of glyphosate-resistant weeds.”
Meanwhile, corn farmers who planted GM insect-resistant seed varieties used about 11.2 percent less insecticide than farmers who did not plant GM corn. However this does not account for the use of neonicotinoid insecticides used as a seed treatment on GM seeds.
Overall, Ciliberto said he was surprised by the extent to which herbicide use had increased. The adoption of GM soybeans correlated with a negative impact on the environment as increased herbicide use also increased contamination of local ecosystems.
(Source: University of Virginia)