Monsanto Co.’s experimental genetically engineered wheat, never approved for sale, has been found growing in a second U.S. state, and regulators said on Friday they could not explain how the plants escaped field trials that ended almost a decade ago.

About a year after discovery of the company’s unapproved wheat in a single Oregon field disrupted U.S. wheat export sales, the GMO wheat has also been found in Montana, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service said on Friday.

APHIS launched an investigation into the Montana discovery on July 14, said Bernadette Juarez, director of investigative and enforcement services for APHIS.

The wheat was found growing at a research facility for Montana State University in Huntley, where field trials of Monsanto’s wheat were conducted between 2000 and 2003, she said in a news conference.

After conclusion of field trials, crop developers like Monsanto are obligated to inform regulators of any “volunteers,” or plants that grow on their own following a previous harvest, Juarez said.

Monsanto said in a statement that it and Montana state notified APHIS of the unintended GMO wheat and were “cooperating fully” with the government investigation.

USDA officials said there are no health and safety concerns from Monsanto GMO wheat, and that they do not believe the wheat has entered commerce. The area where it was found primarily produces sugar beets and barley, not wheat, Juarez said.

The varieties of wheat in Montana differ significantly from Oregon’s, but both contain Monsanto’s herbicide-tolerant trait.

There is no commercially approved genetically modified wheat. The wheat in question was developed by Monsanto to withstand treatments of its Roundup weed killer, but the company never commercialized the “Roundup Ready” wheat. International buyers threatened to boycott U.S. wheat if the product was introduced to the marketplace.

Monsanto said in 2004 that it was ending efforts to commercialize the GMO wheat, and the wheat was supposed to have been destroyed or stored securely.

Monsanto and several other companies are still trying to develop a biotech wheat acceptable to the market. APHIS said on Friday it was stepping up oversight of those field trials.

Word of the wheat in Montana comes after last year’s discovery by an Oregon farmer of the GMO wheat in his field. That discovery prompted South Korea and Japan to temporarily halt purchases of U.S. wheat due to fears of contamination.

APHIS said on Friday that despite a “comprehensive” investigation, the agency has not determined how the biotech wheat came to grow in Oregon. No field trials were ever authorized on that Oregon farm.

Juarez said there would not be any penalties or disciplinary action against Monsanto for the Oregon incident.

Several farmers sued Monsanto, however, accusing the company of failing to protect the market from contamination.

The parties agreed to settle, prior to the announcement of the Montana wheat discovery.