A federal judge Monday ordered an immediate halt to sales of genetically modified alfalfa seed

The ruling by U.S. District Judge Charles Breyer follows his decision last month that the U.S. Department of Agriculture had not fulfilled a requirement to prepare a full environmental impact statement before approving the crop's commercial release in June 2005. The alfalfa seed, developed by Monsanto Co. and Forage Genetics International, is designed to resist Monsanto's popular herbicide, Roundup.

The Center for Food Safety, based in Washington, D.C., filed the lawsuit challenging the agriculture department's approval. Among the plaintiffs are Phillip Geertson of Adrian, Ore., an alfalfa grower and seed producer.

Conventional and organic alfalfa growers argued that the modified seed could crossbreed with conventional varieties, endangering export markets that prohibit genetically modified varieties.

Oregon ranks 11th among states in alfalfa production, with more than $230 million in sales.