Farmers growing genetically modified crops use more pesticides than conventional farmers, according to a new study by the Organic Center in Boulder, Colo. In the past 13 years, 318 million more pounds of pesticides were applied to GE soybean, corn and cotton crops than conventional, according to the report.

“This wasn’t a huge surprise to people who have been following [GE crops],” said Charles Benbrook, Ph.D., chief scientist for the Organic Center. “The herbicide-tolerant crops are not working as well as they were developed to; the plants are becoming more chemical resistant so farmers have to apply higher rates of herbicides,” Benbrook said.

The study used a model to analyze U.S. Department of Agriculture pesticide use data to compare the amounts of pesticides applied to GE crops versus conventional.

Introduced commercially 13 years ago, GE seeds are manufactured to control weeds in several ways. Herbicide tolerant (HT) crops are designed to withstand application of weed killers such as Roundup Ready. But in high-weed areas such as the South East, more herbicide is necessary to kill the weeds. “When farmers just use one herbicide they push all of the diversity out and nature will adapt. In the South East, we could be just a few years away from a Roundup ready collapse with cotton, corn and soybean crops,” Benbrook said.

In 2008, GE crop acres required more than 26 percent more pounds of pesticides per acre than conventional plant varieties, according to the report. “This is going to force a lot of people to see that there’s trouble down on the farm,” Benbrook said. “As the resistance spreads and [farmers] need to use stronger chemicals, it will become a public health issue.”

Organic farmers address weed control with crop rotation, cover crops and they “accept a little weed pressure in their fields,” Benbrook said. “The key to organic farming success in is the diversity of tools [to control weeds] on their farm.”