DES MOINES, Iowa (AP) — A judge’s ruling halting planting of genetically modified sugar beet seeds has left growers feeling uncertain as they wait for federal officials to decide the next step for a crop that provides half of the nation’s sugar supply.

Duane Grant, chairman of the board at the Boise, Idaho-based Snake River Sugar Co., said if a solution can’t be worked out to use the genetically modified seed, his company and its growers fear there isn’t enough conventional seed to plant next year. The company produces about 20 percent of the nation’s beet sugar.

“There has been no incentive, no market, no demand for conventional seed since 2008 and we believe there is not enough conventional seed available for our growers to plant a full crop in 2011,” he said.

U.S. District Court Judge Jeffrey White in California issued his ruling Aug. 13 that put on hold future planting of sugar beets using genetically modified seeds. White’s ruling allows this year’s crop to be harvested and processed, but the current seed crop can’t be planted until the U.S. Department of Agriculture reviews the effect the genetically altered crops could have on other food.

That could take several years. Until then, genetically modified seeds can be stored.

At issue are seeds developed by St. Louis-based Monsanto Co., used to grow about 95 percent of the sugar beet crop. The seeds are engineered to withstand the weed killer Roundup, allowing farmers to reduce the use of other chemicals and limit the practice of tilling fields to kill weeds.

Monsanto seeds also dominate corn and soybean production, but experts said last week’s decision is limited to sugar beets. Some groups hope, though, that the ruling could prompt the USDA to take a broader look at questions involving genetically modified crops.

Monsanto referred questions to Luther Markwart, executive vice president of the American Sugar Beet Growers Association. He said the next move is up to the USDA.

“The message we’re giving people is you have to be patient and let this play out,” Markwart said.

USDA spokesman Caleb Weaver said the agency’s attorneys are reviewing the ruling but haven’t made any decisions.

White’s ruling was the latest step in a lawsuit filed in 2008 by the Center for Food Safety, the Organic Seed Alliance and the Sierra Club challenging the USDA’s regulatory oversight for genetically engineered sugar beets and the potential that the seeds could contaminate other crops.

Sugar beets are planted on more than 1 million acres in 10 states, with Minnesota, North Dakota and Idaho being the top producers.

Robert Green, a North Dakota beet grower, said he didn’t know what would happen next but was confident he would plant sugar beets next spring.

“Sugar beets provide half the sugar for this country, and I don’t believe they will make the requirements so stringent people will go without sugar,” said Green, who farms near St. Thomas in far northeastern North Dakota.

Grant, whose Snake River Sugar Company has about 1,000 growers in Idaho, Washington and Oregon, said the USDA must act quickly so growers can plan for next year.

“We have a limited ability to influence them, and we will be dependent on their timely decision-making process,” Grant said.

The ruling comes two months after the U.S. Supreme Court lifted a ban on the planting of genetically modified alfalfa seeds. The USDA still must abide by a lower court’s order to conduct an environmental impact study on use of the seeds.

Representatives of the groups that filed the sugar beet lawsuit said their suit and the alfalfa case shows the USDA hasn’t properly overseen genetically modified crops.

Matthew Dillon, founding director of the Organic Seed Alliance, said he would like the USDA to review of all genetically modified crops.

“We hope the government will sit down and look at what coexistence will look like. And past administrations have skirted the issue, believing that somehow, magically, plants won’t cross and these two types of systems can coexist without contamination,” Dillon said.

But even some who agree with Dillon don’t believe challenges to such crops as corn or soybeans are likely.

George Kimbrell, an attorney for the Center for Food Safety, noted that corn and soybeans are annual crops that are overwhelmingly genetically modified and self-pollinating. Also, he said, farmers typically rotate annually between the two crops. Those factors reduce the risk of contamination, Kimbrell said.

Another issue is that genetically modified corn and soybeans have been dominant for at least a decade, while alfalfa and sugar beat seeds are among the newest to be approved.

“Once it’s deregulated and out there, it’s not easy to do a challenge,” Neil Carman, clean air director of the Sierra Club, said. “The problem is that with some of those crops, the horse got out of the barn before we were ready to file legal cases.”