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. 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. The roadside plants apparently start growing when seeds blow from fields or fall out of trucks carrying the crops to market. In the plains of Canada, where canola is widely grown, roadside biotech plants resistant to the herbicide Roundup have become a problem, said Alexis Knispel, who has just completed a doctoral dissertation on the subject at the University of Manitoba. Some farmers, she said, have had to return to plowing their fields to control weeds - a practice that contributes to soil erosion - because they can no longer use Roundup to control the stray canola plants. She also said the proliferation of roadside canola would make it difficult to keep organic canola free of genetically engineered material. The biotech canola has also been found growing in Japan, which does not even grow the crop, only imports it. Scientists have also reported that genetically engineered grass established itself in the wild in Oregon.