Tennessee on Thursday imposed restrictions on the use of dicamba, a flagship pesticide for Monsanto Co, to become 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.
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.