THE world’s most popular herbicide is losing its knockout punch. More and more weeds are evolving resistance to glyphosate – originally marketed by 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 , 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.
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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 . 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.
Where diverse weed control is practiced, however, resistance has not yet developed. In most of Canada, for example, farmers grow glyphosate-resistant canola in rotation with wheat and barley. They vary the herbicides used depending on the crop grown, and glyphosate-resistant weeds are unknown.
To keep resistant weeds from spreading may require intervention from governments or farmers’ associations. “You’re going to need some sort of collective management,” says , an environmental economist at Portland State University in Oregon. GM crops and herbicides are already widely used, but they can still be regulated, or as Ervin puts it: “While the cat is out of the bag, it’s possible to control the range of the cat.”
