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Jerry McCulley-Roundup herbicide
In this June 1, 2010 photo, central Illinois corn farmer Jerry McCulley refills his sprayer with the weed killer glyphosate on a farm near Auburn, Ill. A handful of hardy weeds have adapted to survive glyphosate _ sold as Roundup and a variety of other brands _ which many scientists say threatens to make the ubiquitous herbicide far less useful to farmers. (AP Photo/Seth Perlman)

Since the introduction of genetically modified crops, American farmers have used more than 400 million pounds of agricultural chemicals, leading to widespread weed and insect resistance, according to a study released this week.

The study, by Washington State University researcher Charles Benbrook, was the first to examine federal data on pesticide use, and was published in the peer-reviewed journal, Environmental Sciences Europe.

The agricultural biotechnology industry, including Creve Coeur-based Monsanto Co., has long said that their products reduce overall pesticide use. But in recent years, according to Benbrook's study, herbicide use has shot up as weeds become resistant, forcing farmers to apply more.

Monsanto spokesman, Thomas Helscher, declined comment except to say the company would review the study.

Benbrook's analysis found that Bt crops – those genetically engineered to repel insects – reduced insecticide use by 123 million pounds, or 28 percent.

At the same time, Benbrook found, farmers increased herbicide use by 527 million pounds over the same period. (Herbicides kill weeds. Insecticides kill bugs and pests. Both are pesticides.)

Overall, Benbrook concluded, farmers have increased pesticide use by 404 million pounds.

Benbrook said that glyphosate, the main ingredient in Monsanto's Roundup herbicide, accounted for most of the increase.

In 2005, for example, total herbicide use in soybean fields was 1.17 pounds per acre. In 2006, it was 1.42 pounds per acre, or a jump of about two-tenths of a pound. The last year that federal researchers surveyed pesticide use in soybeans was 2006, so from that point to 2011, Benbrook assumed a total jump of another two-tenths of a pound.

“I was pretty conservative,” he said. “In terms of overall herbicide use, the model projects there were 90 million more pounds applied on the GE crop acres than would have been applied in 2011 had all that land been planted to conventional crops.”

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