Moschini, Perry co-author Science Advances article on GE crops and pesticide use

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Researchers at the Center for Agricultural and Rural Development (CARD) at Iowa State University have co-authored an article detailing the changes in herbicide and insecticide use among farmers growing genetically engineered (GE) crops.

The researchers found that farmers growing GE crops decreased their use of insecticides but increased their use of herbicides.

The article, which was co-authored by GianCarlo Moschini, professor of economics and the Pioneer Chair in Science and Technology Policy, and Edward Perry, a former graduate research assistant at CARD, has just been released in the August 31 issue of Science Advances, a journal of the American Association for the Advancement of Science. David Hennessy of Michigan State University and Federico Ciliberto of the University of Virginia are also co-authors of the article.

GE crops have accounted for more than 80% of planted soybean and maize in the United States since 2008. However, the effects of planting GE crops on pesticide use is not well understood.

In order to shed light on the subject, Moschini, Perry and colleagues assembled farm-level data from more than 5,000 maize and soybean farmers per year, from 1998 to 2011, focusing on directly observed pesticide application rates. “We differ in term of the data we use and the methodology we apply,” Moschini said. “The statistical fixed-effects model that we can estimate, based on these extensive data, permits a useful comparison between the choices of farmers who adopt GE varieties and farmers who plant non-GE varieties, while accounting for many possible confounding effects.”

The data led the researchers to the conclusion that GE crops are affecting herbicide and pesticide application rates, with adopters of GE insect-resistant maize using 11.2% less insecticide than nonadopters. They also found that adopters of GE glyphosate-tolerant soybeans used 28% more herbicide than nonadopters.

“Overall, we confirm the view that GE maize adoption has contributed to reducing insecticide use. Like other studies, we also find that GE varieties have massively increased glyphosate use, while reducing the use of other herbicides,” Moschini said. “But our study is the first to document that these impacts have changed significantly over time. For both soybeans and maize, GE adopters have been using increasingly more herbicide than nonadopters.”

Why are GE adopters using more herbicide than nonadopters? Moschini said there was a lot of factors at work. “One consideration is that glyphosate has become progressively cheaper relative to other herbicides; but possibly the most significant explanation, particularly in the latter part of the period we investigate, is that weeds resistant to glyphosate became more prevalent, and this development has had a greater impact on GE adopters,” Moschini said. “A useful piece of evidence is the number of plots with GE varieties that used exclusively glyphosate. We find that this fraction has declined significantly in recent years. Also, we find that the quantity of herbicides other than glyphosate used by GE adopters significantly increased, relative to the use by nonadopters, over time,” he said.

(Released September 2016)