The use of herbicides in the production of genetically modified corn, cotton and soybeans is increasing, according to a new study published by Washington State University research professor Charles Benbrook. This analysis, based on publicly available data from the U.S. Department of Agriculture’s National Agriculture Statistics Service, is the first peer-reviewed, published estimate of the impact of genetically engineered, herbicide tolerant crops on pesticide use.

The findings suggest that pesticide reduction seen earlier in the adoption of these crops has reversed. Benbrook writes that the emergence and spread of glyphosate-resistance weeds is strongly correlated with the upward trajectory in herbicide use.

“Resistant weeds have become a major problem for many farmers reliant on GE crops, and they are now driving up the volume of herbicide needed each year by about 25 percent,” Benbrook said.

Benbrook’s analysis shows that over-reliance on herbicide-tolerant crops has led to shifts in weed communities and spread resistant weeds, which has forced farmers to increase herbicide application rates, (especially glyphosate), spray more often and add new herbicides that work through an alternative mode of action into their spray programs.

Significant Findings

Of the findings that Benbrook researched, here are some of the top results he found.

  • Over the first six years of commercial use (1996-2001), HT and Bt crops reduced pesticide use by 31 million pounds, or by about 2 percent, compared to what it likely would have been in the absence of GE crops.
  • Bt crops have reduced insecticide use by 10 million to 12 million pounds annually over the past decade. From 1996-2011, Bt crops have reduced insecticide use on the three crops by 123 million pounds, or about 28 percent.
  • The annual per acre reduction in insecticide use on acres planted to Bt corn and cotton has trended downward since 1996, because of the shift toward lower-dose insecticides and the expansion of Bt corn onto acres that would not likely be treated with an insecticide.
  • The relatively recent emergence and spread of insect populations resistant to the Bt toxins expressed in Bt corn and cotton has started to increase insecticide use, and will continue to do so in response to recommendations from entomologists to preserve the efficacy of Bt technology by applying insecticides previously displaced by the planting of Bt crops.
  • HT crops have increased herbicide use by 527 million pounds over the 16-year period (1996-2011). The incremental increase per year has grown steadily from 1.5 million pounds in 1999, to 18 million five years later in 2003, and 79 million pounds in 2009. In 2011, about 90 million more pounds of herbicides were applied than likely in the absence of HT, or about 24 percent of total herbicide use on the three crops in 2011.

One of the concerns resulting from the discovery of this data is that farmers are increasingly returning to using older chemistries that are considered higher risk, Benbrook said.

Click here to view a summary of the study’s major findings.