Genetic drift of seeds, pollen is a growing concern for farmers

Along with chemical drift, farmers face the problem of genetic drift — the migration of genetically modified seeds or pollen into fields of organic or conventional crops.

In one of the largest contamination settlements to date, a unit of Bayer A.G. agreed in 2011 to pay $750 million to U.S. rice farmers who claimed their crops were tainted by a Bayer GM rice strain, making them unmarketable overseas.

More recently, wheat farmers in Oregon have filed class action suits against Monsanto Co. after discovering an experimental strain of the company's herbicide-resistant wheat growing in their fields. The farmers claim the GM wheat, which has not been approved for sale, escaped from Monsanto test fields and has damaged their wheat exports to countries that do not permit GM crops.

Monsanto has moved to dismiss the complaints, which are pending in U.S. District Court in Kansas City, Kan.