In 2008, the USDA approved planting of Monsanto’s Roundup Ready sugar beet, equipped with a gene that allows them to withstand unlimited doses of Monsanto’s Roundup herbicide.

The sugar trade promised to be a big money maker for genetically modified (GM) seed giant Monsanto, as these beets — a special super-sweet variety, not the kind you find at the farmers market — account for 44 percent of U.S. sugar production.

Sure enough, Monsanto rapidly conquered the market. By this year’s spring planting, Monsanto’s patented GM seeds covered a jaw-dropping 95 percent of sugar beet fields. (Monsanto has managed to quietly turn the American sweet tooth into a gold mine — it also dominates the seed market for corn, the source of the number-one U.S. sweetener, high-fructose corn syrup.)

But back in August, Monsanto suffered yet another of a continuing line of setbacks, when a federal judge effectively nixed the USDA’s approval of GM sugar beets. The agency had failed to adequately assess the environmental impact of planting the high-tech seeds, the judge ruled.

On Monday, a USDA economist released a report (via Bloomberg) estimating that the ban on GM sugar beet seeds would cut U.S. total sugar production by 20 percent in 2011, due to the the “limited availability of conventional seed.”