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The rapid adoption of a single weed-killer for the vast majority of crops harvested in the United States has given rise to superweeds and greater pesticide use, a new study suggests. And while crops engineered to manufacture an insect-killing toxin have reduced the use of pesticides in those fields, the emergence of newly resistant insects now threatens to reverse that trend.

Farmers spray the herbicide glyphosate, widely sold under the Monsanto brand Roundup, on fields planted with seeds that are genetically engineered to tolerate the chemical. Found in 1.37 billion acres of corn, soybeans, and cotton planted from 1996 through 2011, this “Roundup Ready” gene was supposed to reduce or eliminate the need to till fields or apply harsher chemicals, making weed control simple, flexible, cheap, and less environmentally taxing.

In fact, this system has led farmers to use a greater number of herbicides in higher volumes, according to the study, published this week in the peer-reviewed journal Environmental Sciences Europe.

“The reason farmers adopted the technology as rapidly as they did is, in the early years, it worked very well – you couldn’t screw it up,” said the study’s author, Charles Benbrook, a research professor at Washington State University’s Center for Sustaining Agriculture and Natural Resources. Indeed, in the first six years of commercial use, crops engineered to tolerate herbicides or resist insects reduced pesticide use by 31 million pounds, or about 2 percent, according to Dr. Benbrook’s analysis of data from the Department of Agriculture.

Yet by 2011, herbicide-resistant crop technology had increased herbicide use in the United States by 527 million pounds, according to the paper. Corn and cotton crops engineered to fend off rootworm, European corn borer and other crop-destroying insects by manufacturing toxins from the soil bacterium Bacillus thuringiensis, or Bt, reduced insecticide applications by 123 million pounds, or about 28 percent, from 1996 to 2011.

But over all, pesticide use last year on each acre planted with a genetically engineered crop was about 20 percent higher than on acres not planted with genetically engineered crops. And today, Dr. Benbrook writes, “a majority of American soybean, maize, and cotton farmers are either on, or perilously close to a costly herbicide and insecticide treadmill.”