CHICAGO (Reuters) – Tennessee on Thursday imposed restrictions on the use of dicamba, a flagship pesticide for Monsanto Co, becoming the fourth state to take action as problems spread over damage the weed killer causes to crops not genetically modified to withstand it.

Dicamba is sprayed by farmers on crops genetically modified to resist it but it has drifted, damaging vulnerable soybeans, cotton and other crops across the southern United States. Farmers have fought with neighbors over lost crops and brought lawsuits against dicamba producers.

Arkansas banned its use last week and Missouri, which initially halted dicamba spraying, has joined Tennessee with tight restrictions on when and in what weather spraying can be done. Kansas is investigating complaints.

“We’ve had damage across just about every acre of soybeans we farm in southeast Missouri,” said Hunter Raffety, a farmer in Wyatt, Missouri. “In our small town, the azaleas, the ornamentals, people have lost their vegetable gardens. It’s a big problem.”

He suspects between 3,000 and 4,000 acres of soybeans on the 6,000 acres he and his family farm have sustained damage, evidenced by the leaves of plants constricting into cup-like shapes.

Monsanto, which said it has spent years working to make dicamba stickier and limit drift when it is sprayed, is campaigning to overturn the bans. It blames early-adoption headaches similar to wind drift and cross-contaminated farm equipment problems the company faced when it launched its popular Roundup Ready glyphosate-resistant crops two decades ago.

“In almost every technology in that first year there are kinks that you need to work out,” Robb Fraley, Monsanto’s chief technology officer, said on a news media call.

He said many of the dicamba issues are caused by farmers not following application labels, using contaminated equipment or buying older formulations of dicamba that are cheaper but more prone to drift.

The company, together with BASF SE and DuPont, which also produce dicamba-based weed killers, has agreed to additional safeguards for product use, Missouri Director of Agriculture Chris Chinn said in a statement.

The dicamba problem is the latest regulatory woe for Monsanto after California last month announced it would list glyphosate as a probable carcinogen in the state.

“It’s not good for Monsanto – if anything, this is more likely to lead to lawsuits rather than additional sales,” Jonas Oxgaard, an analyst with asset management firm Bernstein, said regarding the dicamba launch woes.