Superweeds linked to rising herbicide use in GM crops

Seed Daily via SPX: A study published this week by Washington State University research professor Charles Benbrook finds that the use of herbicides in the production of three genetically modified herbicide-tolerant crops - cotton, soybeans and corn - has actually increased.

This counterintuitive finding is based on an exhaustive analysis of publicly available data from the U.S. Department of Agriculture's National Agriculture Statistics Service. Benbrook's analysis is the first peer-reviewed, published estimate of the impacts of genetically engineered (GE) herbicide-resistant (HT) crops on pesticide use.

In the study, which appeared in the the open-access, peer-reviewed journal "Environmental Sciences Europe," Benbrook writes that the emergence and spread of glyphosate-resistant weeds is strongly correlated with the upward trajectory in herbicide use.

Marketed as Roundup and other trade names, glyphosate is a broad-spectrum systemic herbicide used to kill weeds. Approximately 95 percent of soybean and cotton acres, and over 85 percent of corn, are planted to varieties genetically modified to be herbicide resistant.

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

Palouse fields in eastern Washington after the use of herbicides, shot by Bala, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 Generic license

Weed resistance could mean herbicide is futile

Bob Holmes in New Scientist: The world's most popular herbicide is losing its knockout punch. More and more weeds are evolving resistance to glyphosate - originally marketed by Monsanto as Roundup - but the problem could have been forestalled by farming practices enriched by a better understanding of evolution. This is a serious problem. "Glyphosate is as important to world food production as penicillin is to human health," says Stephen Powles, a plant scientist at the University of Western Australia in Perth.

In 1996, Monsanto began selling crop varieties genetically modified to contain a gene for glyphosate resistance. This enabled farmers to spray glyphosate - lethal to plants yet non-toxic to animals - on their fields to kill weeds without damaging the crops, even during the growing season.

Today nearly 100 million hectares worldwide are planted with glyphosate-resistant crops. In much of the south-eastern US, as well as Brazil and Argentina, farmers grow glyphosate-resistant corn, soybeans and cotton year after year and have come to rely almost exclusively on this herbicide. This has encouraged at least nine species of weed to evolve their own glyphosate resistance, to the point where some farmers can no longer control weed infestations.

The solution, as any evolutionary biologist will tell you, is for farmers to vary weed-control practices so that weeds face a number of evolutionary pressures instead of just one. Monsanto recommends precisely this in its instructions to farmers. But farmers have been reluctant to reduce their use of an effective herbicide for an intangible future benefit, especially when few have experienced glyphosate-resistant weeds….

Backlit spring weeds, shot by Downtowngal, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license