YAKIMA, Wash. (AP) -- Several Washington wheat growers filed suit Thursday against Monsanto Co. over the unauthorized release of genetically modified wheat, claiming the discovery of the wheat in an Oregon field last week has damaged sales of exports.

The lawsuits, filed two days after a Kansas farmer filed a similar lawsuit against the company, seek class-action status on behalf of all growers of soft white wheat who may have been harmed by the release of an unapproved product.

Soft white wheat is a variety popular with growers in the Pacific Northwest, where nearly 90 percent of the crop is exported to Asian markets for noodles and crackers.

"We farmers cannot stand idly by while companies like Monsanto destroy our export markets and our economy," said Tom Stahl, a fourth-generation Washington wheat farmer from Waterville.

Genetically engineered, experimental wheat was found growing in an 80-acre field in Oregon last week. The wheat was the same strain as one designed by Monsanto to be resistant to herbicides. It was tested in Oregon and several other states through 2005 but was never approved by the government.

The U.S. Department of Agriculture has said the Oregon wheat is safe to eat and there is no evidence that modified wheat entered the marketplace. No genetically engineered wheat has been approved for U.S. farming.

Since the announcement of the discovery of the genetically modified wheat in Oregon, Japan — one of the largest export markets for U.S. wheat growers — suspended some imports. South Korea said it would increase its inspections of U.S. wheat imports.

Monsanto has called the emergence of the genetically modified strain an isolated occurrence and said it likely was the result of an accident or deliberate mixing of seeds.

On Thursday, the St. Louis-based company said the lawsuits were premature given that the strain was limited to one field in Oregon and that none of the wheat had entered commerce.

Kyle McClain, Monsanto chief litigation counsel, said the company's process for closing out its wheat development program was government directed, rigorous and well documented.

"Given the care undertaken, no legal liability exists and the company will present a vigorous defense," he said in a statement.

In addition to Stahl, the Waterville farmer, the lawsuits filed Thursday in U.S. District Court in Spokane name the plaintiffs as Joe Ludeman of Waterville, Dreger Enterprises of Creston, Wahl Ranch of Lind, and the Center for Food Safety, a nonprofit group with an office in Portland, Ore., that promotes organic and sustainable agriculture and safe food practices.