Sept 17 (Reuters) - The detection of a small amount of genetically modified material in a Washington state farmer’s non-GMO alfalfa crop constitutes a “commercial issue” only and does not warrant any government action, the U.S. Department of Agriculture said on Tuesday.

The Washington state farmer had complained in late August to state agricultural officials that his alfalfa hay had been rejected for export sale because of the presence of a genetically modified trait that makes the crop resistant to herbicide.

The event triggered a wave of concern from consumer and agricultural groups who have fought the government for nearly a decade to keep biotech alfalfa from contaminating conventional and organic supplies.

Crop experts have warned that the confirmation of contamination threatens U.S. sales of alfalfa feedstock to many Asia nations who reject GMOs, and some are encouraging farmers to test every bag of seed they buy before they plant.

But USDA said the detection of Monsanto Co’s patented Roundup Ready herbicide-tolerant trait in the Washington farmer’s non-GMO alfalfa crop should be addressed by the marketplace and not the government.

“The agriculture industry has approaches to minimize their occurrence and manage them when they occur,” the statement said.

Alfalfa, a livestock feed crop, routinely ranks among the top five crops in the nation in terms of farmgate value and total acreage planted. It is the first perennial biotech crop to be approved, and its perennial nature makes it even more of a contamination risk, critics have charged.

Washington agriculture officials notified APHIS late Friday that they had confirmed a “low-level” presence of a genetically engineered trait in what the farmer thought was a non-GMO crop.

State agriculture officials did not identify the level of contamination, but in a letter to APHIS said it was “within ranges acceptable to much of the marketplace.”

Roundup Ready alfalfa was initially approved by USDA in 2005. But environmental groups and some seed companies sued USDA in 2006 and successfully forced the agency to rescind its approval after a federal court found USDA had not conducted a thorough environmental review as required before approving the product.

After completing an environmental review, the government in 2010 considered approving GMO alfalfa with certain planting restrictions to try to isolate it from non-GMO alfalfa. Instead, USDA approved unrestricted planting in January 2011.

The amount of GMO contamination that might be present in conventional alfalfa is not known. But a December 2011 report by Stephanie Greene, a geneticist with the USDA Agricultural Research Service, ARS, said that after Roundup Ready alfalfa was first deregulated in 2005 industry testing of conventional seed lots found levels of contamination as high as 2 percent.

George Kimbrell, senior attorney with The Center for Food Safety, which brought the lawsuit against the government that led to the temporary injunction on alfalfa sales, said the organization might renew its litigation over alfalfa contamination concerns in light of the events in Washington state.