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According to the Canola Council of Canada, 80 per cent of the canola grown in Western Canada is genetically modified. ((Gregory Bull/Associated Press))

Feral canola plants with genetic modifications that make them resistant to herbicides appear widespread along roadsides in North Dakota, a new study has found.

Of 406 plants collected along 5,400 interstate, state and county roads in July, 86 per cent tested positive for at least one of two transgenic proteins that make canola resistant to glyphosate herbicides such as Roundup, reported the researchers Friday at the annual meeting of the Ecological Society of America in Pittsburgh.

"There were also two instances of multiple transgenes in single individuals," said co-author Cynthia Sagers, an associate professor of biological sciences at the University of Arkansas, in a statement.

"Varieties with multiple transgenic traits have not yet been released commercially, so this finding suggests that feral populations are reproducing and have become established outside of cultivation."

Researchers from North Dakota State University, California State University, Fresno and the U.S. Environmental Protection Agency were also involved in the study.

Concern over potential 'superweeds'

Environmental groups such as Greenpeace have long expressed concerns about the spread of genetically modified plants and their genes. They say if wild plants crossbreed with transgenic crops that are herbicide-resistant, "superweeds" resistant to herbicides could form.

According to the Canola Council of Canada, herbicide-resistant genetically modified canola makes up 80 per cent of the canola crop in Western Canada by acreage because it makes weed control easier.

The council's website confirmed genetically modified canola has crossed with other types of canola and in some cases, growers have found canola plants with multiple resistance to herbicides.

"These plants are easily controlled with other herbicides that are readily available," it added.

It said there are no cases of GM canola crossing with weeds in Canada.