MANKATO — Farmers across the state and the Midwest have filed complaints of a new dicamba herbicide sprayed on neighbors' fields that has spread onto their soybeans, causing damage to the plants.

"There have been over 200 reports of damage that have come into the Department of Agriculture in nearly 50 counties. There is speculation that only 30 percent of damaged fields have been reported," said Michael Petefish, president of the Mankato-based Minnesota Soybean Growers Association.

The growing concern over dicamba and other herbicides being developed to kill weeds that have become resistant to other weed killers led the association to form a dicamba task force. They hope to learn the reasons for the damage and to find the best ways to fight resistant weeds while protecting crops.

"It's a tough problem. It's hard to even determine how much damage is done," Petefish said. That's because the damaged beans often aren't killed but their leaves cup and shrivel, reducing the harvest. Petefish said when damaged soybeans are harvested, it's hard to know what they would have produced if they hadn't been damaged.

The dicamba herbicide is produced by Monsanto, which also modified a seed that produces soybeans that are not harmed by the dicamba spray. But neighboring fields without those type of soybeans are at risk if dicamba gets on them.

Petefish said part of the lesson is that farmers became too dependent on Roundup herbicide for fields. Roundup has been widely used on soybeans that are modified to be unharmed by Roundup, but those plants are not resistant to dicamba.

"I think we learned from Roundup that it worked too well. We overused it."

Petefish said relying so heavily on only Roundup eventually led some weeds to find ways to become resistant to the herbicide, leaving chemical companies and farmers searching for new weed killers.

"Repeated use of a single mode of action, given a long enough time, it's almost inevitable to not create resistance."

He said part of what he hopes the task force accomplishes is to provide methods that farmers can use to control weeds while slowing their resistance. "Weeds will adapt, so you can't keep doing the same thing. I think with new products, if you combine them with two or three modes of action, you'll limit resistance."

Problems with dicamba also have surfaced in the south, with Texas grape growers and Missouri peach farmers complaining the spray damaged or killed their fruit crops.

At least two states have banned its use and Monsanto has developed a new version, not yet approved, that it says is less prone to drifting. But the company's response so far has been criticized by many.

"They're definitely are not embracing responsibility with open arms by any means," Petefish said.

He expects to see a growing number of lawsuits over dicamba. But he said no one is yet sure exactly why the damage happens. It could be that farmers or co-ops applying dicamba aren't following application directions carefully or that the herbicide was not tested enough for various weather and soil conditions. "I think it's probably some of both"

"Who do you sue? Neighbors, Monsanto, co-ops that applied it?" Petefish asked.

He said problems in Minnesota are less than in many southern states where warmer weather year-round has helped produce some highly resistant monster weeds.

"A lot of people I know opted not to pursue the (dicamba) technology this year. We don't have the real hard resistant weeds here yet. Luckily we have winters," said Petefish, who farms between Owatonna and Rochester.

He said the task force will include farmers who've used dicamba without any problems, farmers whose soybeans have been damaged by it, and farmers whose fields adjoin dicamba soybean fields but haven't seen any damage.

"We'll also have U of M researchers, someone from the ag department and one or two from (the chemical) industry, whether it's Monsanto or others."

He said it's important to find ways to develop and use new weed technology like dicamba without causing harm to crops.

"In the long term we think this is going to be a tool we need to control weeds. So we want to identify exactly what the problem is and try to fix it."

Follow Tim Krohn on Twitter @TimKrohn

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