April 22, 2010

GM technology raises weed concerns in US

Genetically modified (GM) crops yield substantial economic benefits, but the technology could also add to weed problems, according to a report from the National Research Council in the US.

The report warns GM crops could lose their effectiveness unless farmers also use other proven weed and insect management practices.

Benefits seen as a result of growing GM crops include lower production costs, fewer pest problems, reduced use of pesticides, and better yields compared with conventional crops, said the report. But GM crops resistant to the herbicide glyphosate - the main active ingredient in Roundup and other commercial herbicides - could develop more weed problems as weeds evolve their own glyphosate resistance.

The report provides a comprehensive assessment of how GM crops are affecting all US farmers, including those who grow conventional or organic crops. 

Farmers need to adopt better management practices to ensure that beneficial environmental effects of GM crops continue, it added. In particular, farmers who grow GM herbicide-resistant crops should not exclusively rely on glyphosate, but need to incorporate a range of weed management practices, including using other herbicide mixes.

To date, at least nine species of weeds in the US have evolved resistance to glyphosate since GM crops were introduced, largely because of repeated exposure.

David Ervin, professor of environmental management and economics at Portland State University, and chair of the committee that wrote the report, said many American farmers were enjoying higher profits due to the widespread use of certain GM crops and are reducing environmental impacts on and off the farm.

"These benefits, however, are not universal. As more GM traits are developed and incorporated into a larger variety of crops, it is essential we gain a better understanding of how genetic engineering technology will affect US agriculture and the environment now and in the future," he said.

A report published by the US Organic Centre at the end of 2009 concluded GM crops were pushing pesticide use upward at a rapidly accelerating pace. In 2008, land planted to GM crops required over 26% more pesticides per acre than land planted to conventional varieties. The report projects this trend will continue as a result of the rapid spread of glyphosate-resistant weeds.