Responding to more than 700 complaints of crop damage due to pesticide drift, Missouri and Arkansas banned temporarily the use of the weedkiller dicamba, a stunning setback for an herbicide promoted as the answer to fast-growing invasive weeds that are resistant to other chemical controls. Seed and ag-chemical giant Monsanto said the Arkansas ban was premature and told growers, “[T]o ensure your continued access to dicamba, make sure your elected officials and relevant agencies” hear dicamba success stories.
Missouri Agriculture Director Chris Chinn, facing 130 complaints of pesticide drift, ordered an immediate halt to all on-farm use of dicamba on Friday, the same day the Arkansas Legislative Council allowed a 120-day ban on use of dicamba on row crops to take effect. The Arkansas state plant board, with 596 complaints of dicamba misuse on file as of Friday, said the ban will begin on Tuesday and that a maximum fine of $25,000 for misuse will take effect Aug. 1. Tens of thousands of acres are involved in the complaints.
Problems also are reported in Mississippi and Tennessee, said Delta Farm Press.
“We want to protect our farmers and their livelihoods,” said Chinn in announcing the Missouri ban. He asked chemical companies, researchers and farmers “to work with us to determine how we can allow applications to resume this growing season, under certain agreed-upon conditions.”
Complaints about dicamba mushroomed this year, despite EPA approval of new, lower-volatility formulations that would be less likely to vaporize and drift onto neighboring fields. Strains of cotton and soybeans have been genetically engineered to tolerate doses of dicamba, used for half a century against weeds. In 2016, complaints of dicamba drift often were attributed to growers using older, more volatile versions of the herbicide on the new GE crops.
Since April 15, only a BASF formulation of dicamba has been allowed for use on crops in Arkansas. Monsanto sells dicamba in other states. The Missouri ban included BASF and Monsanto versions.
Monsanto, based in St. Louis, said the Arkansas ban was premature because “the causes of crop injury have not been fully investigated.” In a statement, the company said it was concerned by “reports of potential crop injury in Arkansas. In remarks directed to growers in other states, Monsanto said, “Share how important this tool is to your farm and how you are using it responsibly.”
Weed specialist Tom Barber of the University of Arkansas says “the biggest problem is the sensitivity” to dicamba of soybeans not modified to withstand the herbicide. Even a low level of dicamba will cause soybean leaves to “cup,” he wrote in a crop bulletin in June. Drift accounts for most cases of damage, he said, but up to 20 percent of the damaged fields that he examined are “not that easy to figure out,” such as finding symptoms of dicamba a quarter-mile upwind from where it was sprayed. “It is evident that even when applications are made correctly, that is not good enough.”
Arkansas has strict regulations on use of the weedkiller. Users are required to leave a 100-foot buffer around the edges of fields where dicamba is sprayed and a quarter-mile buffer between those fields and fields of sensitive crops downwind.
BASF and Monsanto advise care in spraying dicamba. For example, BASF says the chemical should not be applied if winds exceeding 10 mph are blowing toward sensitive crops, to keep sprayer booms close to the ground and to use only the nozzles approved for the herbicide.
A University of Tennessee weed specialist told DTN that dicamba guidelines are difficult to satisfy. “You can’t spray when there is too much wind, and I think we’re finding that these temperature inversions are a real issue with this movement. And if there is anything under 3 mph, you can’t spray it either,” said weed specialist Larry Steckel. “If you have a lot of acres to spray, that is hard to do. So, on paper, you can make this thing work, but in reality, if you are a typical farmer, it’s a major undertaking trying to get it to work.”