The spread of highly resistant "superweeds" in one of the world's most important bread baskets is being blamed on genetically modified crops.
British scientists have documented more than a dozen cases of weeds in the heartland of the Canadian prairies that are immune to three leading brands of weedkiller.
They believe that if similar GM crops were introduced in the UK, farmers might resort to old herbicides that are highly damaging to wildlife.
English Nature warns in a report published today that GM crops are helping the creation of superweeds. Brian Johnson, a biotechnology adviser for English Nature, said that the accumulation of two or three herbicide-resistance genes in one species – a process known as gene-stacking – is now widespread in Canada and could have dire consequences for British wildlife.
If gene-stacking were to occur in the UK then it could result in farmers using paraquat to kill weeds at the margins of fields, an area considered vital for wildlife. English Nature also believes that the UK's existing separation distance between GM crops of about 50 metres would probably fail to limit the spread of superweeds.
The superweed spreading in the Canadian prairies is a variety of oilseed rape that has accumulated resistance genes by cross-pollination between different GM varieties. The resulting plant is resistant to the broad-spectrum herbicides Roundup Ready, Liberty Link and Clearfield.
Crop plants that become weeds are known as volunteer plants because they persist in a field through seed being spilt from the previous year's harvest. English Nature found that Canadian farmers were now using old herbicides, notably paraquat, to clear their fields for the next crop. Paraquat is particularly toxic to hares.
"We do not yet know how stacked-gene plants would behave either in farmers' fields or in the wild. The European regulatory system has not yet approved GM herbicide-tolerant oilseeds for general release," Dr Johnson said.
Professor Alan Gray, the chairman of the Government's Advisory Committee on Releases into the Environment, said last night he would study English Nature's report before giving approval for companies to grow GM oilseed with a second herbicide-resistant gene. "They would have to show how they would prevent gene-stacking and what they would do to control it if it did occur," Professor Gray said.
Herbicide resistance had been known about for 40 years, but GM crops were different in that it was easier for plants to become resistant to several weedkillers, he said.
The Department for the Environment, Food and Rural Affairs said that gene-stacking could not occur in Britain at the moment because none of the GM crops in UK farm-scale trials could cross-pollinate with other plants containing a different resistance gene.Reuse content