Arkansas’s pesticide regulators have stepped into the middle of an epic battle between weeds and chemicals, which has now morphed into a battle between farmers. Hundreds of farmers say their crops have been damaged by a weedkiller that was sprayed on neighboring fields. Today, the Arkansas Plant Board voted to impose an unprecedented ban on that chemical.

“It’s fracturing the agricultural community. You either have to choose to be on the side of using the product, or on the side of being damaged by the product,” says David Hundley, who manages grain production for Ozark Mountain Poultry in Bay, Arkansas.

The tension — which even led to a farmer’s murder — is over a weedkiller called dicamba. The chemical moved into the weed-control spotlight a few years ago, when Monsanto created soybean and cotton plants that were genetically modified to survive it. Farmers who planted these new seeds could use dicamba to kill weeds without harming those crops.

Farmers, especially in the South, have been desperate for new weapons against a devastating weed called pigweed, or Palmer amaranth. And some farmers even jumped the gun and started spraying dicamba on their crops before they were legally allowed to do so. (Dicamba has long been used in other ways, such as for clearing vegetation from fields before planting.)