Thursday, May 13, 2010

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

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