ASHLAND, Ore. — Unable to find a good solution to protecting their certified organic seed crops from potential contamination from genetically engineered crops, small organic farmers in this Oregon valley are appealing to a higher power: voters.

They wanted to protect their crops from being cross-pollinated by genetically modified ones, and asked voters in two counties to ban the cultivation of GMOs — a move that would drive producer Syngenta out of the Rogue Valley where it grows seed for sugar beets resistant to the popular weed killer Roundup.

Mail-in ballots will be counted in Jackson and Josephine counties on Tuesday.

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.

After about six months, talks broke down, and the organic farmers went ahead with the ballot measure.

Syngenta, a Swiss company with $14.7 billion in worldwide sales, has been joined by other agricultural giants like Monsanto Co., sugar producers like Amalgamated Sugar, timber companies and farm bureaus as far away as Texas. They have pooled more than $900,000 to defeat the measures.

Their media campaign has focused on convincing voters that enforcing the ban would divert scarce revenues away from sheriff’s patrols and jails.

Syngenta referred comment to the Biotechnology Industry Organization. The group’s spokeswoman, Karen Batra, said the ban was “not just an assault on the industry; it is an assault on farming. It is telling one group of farmers that you can’t farm the way that you want or you need or you think is best for your operation.”

The ban’s supporters, who have raised a third of what opponents have, say they want to protect their crops from contamination by genetically engineered pollen, particularly chard and beets, which could be fertilized by Syngenta’s GMO sugar beet pollen. The pollen wouldn’t affect the plants in the ground, but would make it impossible to certify the seeds as organic, reducing their value, whether for sale or planting.

Hoping to forestall a patchwork of agricultural regulation, Oregon Gov. John Kitzhaber signed legislation last year barring counties from enacting GMO bans, exempting Jackson County because a measure was already on the ballot. He appointed a task force to recommend a way forward.

The law didn’t stop opponents in neighboring Josephine County from putting up their own measure. If it passes, they will have to go to court to put it in force.

Chuck Burr grows more than 300 varieties of certified organic seed outside Ashland and is president of the Southern Oregon Seed Growers Association. He said he could not in good conscience try to sell his crop of chard seeds after learning Syngenta had a field close enough to be pollenated by them, and testing was expensive.

“If anybody ever wanted to push small farms out of the valley, that is how they would do it, with GMO crops,” he said.