The GMO wheat discovered growing wild in a Washington State field this spring actually sprouted from two different strains developed by Monsanto, the USDA announced over the weekend. Genetically engineered wheat is not approved for cultivation anywhere in the world, yet volunteer herbicide-resistant plants have been confirmed four times in the U.S. Northwest more than a decade after field trials ended.

In the latest case, USDA said “thorough testing” identified the wheat as Monsanto strains MON 71300 and MON 71800. The MON 71800 strain also was identified in the first U.S. case of rogue GMO wheat, in eastern Oregon in 2013. The same strain was found growing wild in 2014 at a Montana State University research farm in Huntley, Montana. A different strain, MON 71700, was found in 22 wheat plants in a field in Washington State in 2016.