Genetically engineered versions of the canola plant are flourishing in the form of roadside weeds in North Dakota, scientists say, in one of the first instances of a genetically modified crop establishing itself in the wild.

How much of a problem this might be is subject to debate. But critics of biotech crops have long warned that it is hard to keep genes — in this case, genes conferring resistance to common herbicides — from spreading with unwanted consequences.

“If there’s a problem in North Dakota, it’s that these crop plants are becoming weeds,” said Cynthia L. Sagers, a biology professor at the University of Arkansas, who led the study. Results were presented Friday at the annual meeting of the Ecological Society of America.

Canola, whose seeds are pressed to make the popular cooking oil, is a type of oilseed rape developed by breeders in Canada. In the United States, it is grown mainly in North Dakota and Minnesota, though cultivation is spreading.