miércoles, junio 25, 2014

Nature magazine op-ed on weeds


NATURE | EDITORIAL, 11 June 2014  

A growing problem

Without careful stewardship, genetically engineered crops will do little to stop the spread of herbicide-resistant weeds.


Palmer pigweed (Amaranthus palmeri) is not a weed to trifle with. It can reach more than 2.5 metres tall, grow more than 6 centi­metres a day, produce 600,000 seeds and has a tough, woody stem that can wreck farm equipment that tries to uproot it.

It is also becoming more and more resistant to the popular herbicide glyphosate.

The first such resistant population was confirmed in 2005 in a cotton field in Georgia, and the plant now plagues farmers in at least 23 US states. 

There is broad agreement that the spread of these resistant plants has its roots in the widespread adoption of crops engineered to be resistant to glyphosate.

By 2012, glyphosate-resistant weeds had infested 25 million hectares of US cropland. They have also appeared in other countries that have embraced glyphosate-tolerant crops, including Australia, Brazil and Argentina. Blanketing crops year after year in the same herbicide is the perfect way to foster resistant weeds.

Chemical companies have come up with a solution: crops engineered to tolerate multiple herbicides. The likelihood of a weed becoming resistant to more than one chemical, they claim, is very small. And, in an eerie echo of the 1990s discussion around glyphosate tolerance, some even point out that one of the other herbicides being targeted — the choline salt of an old chemical called 2,4-D — has been used for decades with little sign of resistance.

It is a flawed argument. Stacking up tolerance traits may delay the appearance of resistant weeds, but probably not for long. Weeds are wily: farmers have already reported some plants that are resistant to more than five herbicides. And with glyphosate-resistant weeds already in many fields, the chances of preventing resistance to another are dropping.

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