A federal judge on May 3 barred the planting of genetically engineered alfalfa nationwide, ruling that the government didn’t adequately study the biotechnology crop’s potential to mix with organic and conventional varieties.

U.S. District Court Judge Charles Breyer made permanent a temporary ban he ordered in March on alfalfa with genetic material from bacteria that makes the crop resistant to a popular weed killer.

The ruling is a major victory for anti-biotech crusaders, who have been fighting the proliferation of genetically engineered crops. It is the first ban placed on such crops since the first variety–the Flavr Savr tomato–was approved in 1994.

Breyer said the U.S. Department of Agriculture must conduct a detailed scientific study of the crop’s effect on the environment and other alfalfa varieties before deciding whether to approve it