The vote is the latest example of a growing resistance to GMOs from Hawaii to Vermont at a time when genetically modified crops dominate the production of commodities like sugar beets, corn and soybeans. There is no mainstream scientific evidence of a health risk.
"People are becoming more aware of the fact that food in this country is genetically engineered, and they are starting to look into what that might mean in terms of health and the environment," said Laura Murphy of the Environmental & Natural Resources Law Clinic at Vermont Law School.
Big agribusinesses, spending millions, and GMO opponents have traded victories in recent years.
This month, Vermont's governor signed a law to make the state the first requiring disclosure of GMO ingredients in food labels, starting in 2016. The National Conference of State Legislatures reports 84 genetically modified food labeling bills are pending in 30 states.
Since 2004, counties in California, Hawaii and Washington state have adopted bans. In 2012, agribusiness groups defeated ballot measures in California and Washington state to require statewide GMO food labeling. There is now an effort in Oregon to ask voters to require GMO food labeling.
A bill to nullify state labeling requirements is pending in the U.S. House.
The Oregon vote is the latest battle over the future of agriculture. It is set in this picturesque 41-mile-long valley near the California border, where Syngenta has operated in near anonymity since 1993, and organic farmers have tapped a growing demand for local produce free of pesticides.
Organic farmers realized they had a problem in 2012, when Chris Hardy tried to lease some land and learned it was right next to a field leased to Syngenta. It soon became clear Syngenta was spread throughout the valley.
Farmers started gathering signatures for a ballot measure banning GMOs, and asked Oregon State University Extension to help create a mapping system so GMO and organic corps would each be free of the other's pollen.