By Tom Polansek

CHICAGO (Reuters) - An Arkansas judge has ruled that six farmers in the state this summer can spray a weed killer made by Monsanto Co and BASF SE that was blamed for hurting millions of acres of U.S. crops last year.

The decision is the latest twist in the saga surrounding herbicides based on the chemical known as dicamba and immediately sparked concerns about the potential for more damage. Other states are also limiting sprayings of the herbicide, and farmers are suing its manufacturers over crop damage linked to its use last summer.

Dicamba is meant to be used during the summer on soybeans and cotton that Monsanto genetically engineered to resist the chemical. Growers across the U.S. farm belt said last summer that dicamba drifted away from where it was sprayed, damaging crops that could not tolerate the chemical.

In Arkansas, Pulaski County Circuit Judge Tim Fox ruled on Friday the six farmers can spray dicamba-based herbicides past an April 15 cutoff date that applies to the rest of the state, their attorney Grant Ballard said on Monday.

The growers sued the Arkansas State Plant Board last year to nullify the deadline. Fox dismissed the case, following a recent Arkansas Supreme Court decision that the state cannot be a defendant in court, according to Ballard of the firm Ark Ag Law.

However, Fox said the farmers were exempt from the rule anyway because the inability to sue violated their due process rights, Ballard said.

"We look at it as a win," he said. "We hoped every Arkansas farmer that used the technology responsibly would have the option."

Allowing even six Arkansas farmers to spray dicamba during the growing season risks crop damage, said Terry Fuller, a state plant board member.

Arkansas Attorney General Leslie Rutledge said she was disappointed Fox exempted the six farmers but pleased he dismissed their lawsuit.

Monsanto and BASF say their herbicides are safe when used properly.

Monsanto is banking on its product and soybean seeds engineered to resist it, called Xtend, to dominate soybean production in the United States, the world's second-largest exporter.

Story continues

The company hopes Fox's ruling will be extended to all Arkansas growers, said Scott Partridge, vice president of global strategy. In February, an Arkansas judge dismissed a Monsanto lawsuit aiming to block the state's restrictions.

The case is Michael McCarty et al v Arkansas State Plant Board et all, Pulaski County Circuit Court, Arkansas, 60CV-17-6539.

(Reporting by Tom Polansek; Editing by Richard Chang)