New Scientist

Genetically-modified superweeds "not uncommon"

15:34 05 February 02

James Randerson

Oilseed rape plants resistant to three or more herbicides are "not uncommon" in Canada, says

a report commissioned by English Nature, the UK government's advisory body on conservation.

The so-called 'superweeds' result from accidental crosses between neighbouring crops that

have been genetically modified to resist different herbicides. Farmers are often forced to resort

to older stronger herbicides to remove them.

Brian Johnson, at English Nature is alarmed by the speed of the process: "This has happened

in three or four years," he says. The report predicts that, in the UK, plants with multiple

herbicide resistance will be "almost impossible to prevent unless the crops are very widely


Adrian Bebb, of Friends of the Earth claims the research leaves a stark choice: "Either we keep

the current separation distances between GM and non-GM crops, in which case contamination

and gene stacking looks certain. Or we can have an effective separation distance - of at least

three miles - in which case GM crops have no commercial future in the UK. There is no third


However, Paul Rylott of biotech company Aventis argues many herbicide tolerant crops are

created through conventional breeding, "GM crops are no different."

He suggests that crossing between conventional varieties could have the same result. But

Johnson notes that resistance bred into plant varieties tends to be much weaker and there is

no evidence of 'superweeds' having been created in this way.

Multiple resistance

Oil seed rape, or canola, is typically alternated on a two-yearly cycle with a cereal crop such as

wheat. Multiple resistant oil seed rape appears as a weed in the following year's crop,

especially around field margins where seeds spilled during harvest can gather.

The Canadian study found that these plants contained resistance genes from up to three GM

varieties - so-called gene stacking. Farmers were forced to resort to a different and much more

persistent herbicide, 2,4-D, to control them.

Multiple resistant 'superweeds' would not be capable of taking over the countryside says

Johnson. "They would only have an advantage in agricultural fields," he says. "But agricultural

land is very important for biodiversity in Britain." So widespread use of persistent herbicides to

remove the 'superweeds' could be disastrous.

The biotechnology industry has admitted being slow to engage in the public debate over GM

crops. "We haven't done a brilliant job in the past of selling the benefits of GM," says Tony

Combes of Monsanto, "Support for GM is dependent on people being able to weigh the

benefits against their concerns."

An opinion poll commissioned by the industry and released on Tuesday suggests that two

thirds of people feel they do not know enough about GM and that many would be more

favourable to the technology if environmental or health benefits could be demonstrated.

15:34 05 February 02

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