Scientists warn of GM superweed risk
Paul Brown, environment correspondent Thursday August 18, 2005
The Guardian

Scientists have identified 15 weed species that are resistant to a herbicide widely used on GM crops and are warning farmers they may become a serious problem unless a strategy for dealing with them is developed.
Some of the most common weed species, including types of ryegrass, bindweed and goosegrass either have some strains with a natural resistance to the widely used GM herbicide glyphosate or have developed one.
Writing in the journal Outlooks on Pest Management, four scientists argue there is a danger that by ignoring the threat these weeds pose, farmers maybe giving them a huge advantage over other plants which are killed by glyphosate.
Even where they did not previously thrive on farmland or were in a minority of weeds, farmers may be creating a new niche for them among arable crops which would allow them to multiply rapidly.
The paper is published alongside an assessment of the three-year farm-scale trials of GM oilseed rape, sugar beet and maize in Britain. All three crops are glyphosate-resistant and, if the American researchers are right, would be troubled by glyphosate-resistant weeds if grown commercially in the UK.
Glyphosate has been used by farmers to kill off weeds for 30 years but since the 1990s, when GM crops were modified to resist glyphosate, its use has mushroomed.
The paper says that worldwide use has increased from 5,000 tonnes a year in 1995 to more than 30,000 tonnes in 2002, and has increased since.
However, intensive use of the herbicide combined with the non-rotation of glyphosate-resistant GM crops is expected to increase the problem and it will develop on "a global scale," the paper says.
The researchers, based at the State University and the Southern Weed Research Unit in Mississippi, are concerned that the widespread usefulness of an extremely efficient weedkiller will be lost if farmers do not take precautions.
"The problem of glyphosate-resistant weeds is real, and farmers have to realise that the continuous use of glyphosate without alternative strategies will likely result in the evolution of more glyphosate-resistant weeds.
"Even in the short term no one can predict the future loss of glyphosate efficiency due to weed species shifts and evolution of glyphosate resistance," says Vijay Nandula in the conclusion to the paper.
He advises farmers to treat land with additional herbicide to kill off the weeds before they multiply sufficiently to cause a problem.

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