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In the first officially confirmed case of its kind, weeds in Canada have
become resistant to three kinds of herbicide. The plants picked up genes from
three different, genetically modified varieties of the rapeseed crop canola. In
1997, a farmer in Alberta planted separate fields, each 30 metres apart, with
canola that resisted either Monsanto’s Roundup herbicide, Cyanamid’s Pursuit or
Aventis’s Liberty. In 1998, he found weeds that resisted two herbicides, and
last year, weeds that resisted all three. Only more toxic herbicides, such as
2,4-D, will control them. Companies that market herbicide-resistant crops have
claimed their products would make such toxic chemicals unnecessary.