Federal regulators on Friday announced a new enforcement strategy meant to stop manufacturers from passing off synthetic fertilizers as organic.

In a memo to farm certifiers obtained by The Bee, Barbara Robinson, the chief of the U.S. Department of Agriculture’s organic program, mandated third-party audits of all fertilizer makers selling to the organic market.

Leaders of California Certified Organic Farmers, the state’s top organic certifier, applauded the move. They traveled to Washington, D.C., on Feb. 11 to press Robinson’s agency for a crackdown on unscrupulous fertilizer companies.

“We’re glad that they’ve acted in such a timely fashion,” said spokeswoman Jane Baker.

The Bee reported in December on a state investigation that caught a large organic fertilizer maker spiking its product with synthetic nitrogen, which is cheap, difficult to detect and banned from organic farms.

Robinson’s memo Friday confirmed that the USDA is investigating another major producer, Bakersfield’s Port Organic Products Ltd., which was raided by federal agents in January. Any farm that continues to use the company’s products is jeopardizing its organic status, the memo said.

Port Organic may have accounted for as much as half the liquid organic fertilizer market in California, according to industry sources.

Chris Simas, who sells organic fertilizer for the Tremont/Lyman Group in Woodland, said local growers have recently begun demanding laboratory analyses of the products they use on their fields.

“People are just being very cautious about what they’re doing,” he said.

State Sen. Dean Florez, D-Shafter, held a Senate Food and Agriculture Committee hearing Feb. 3 on the issue, which he said threatens the public’s confidence in organic food.

California is by far the largest U.S. producer of organic fruits, nuts and vegetables.