Missouri has tightened its rules for dicamba, permitting use of the herbicide only during the day and if winds are mild, as agriculture officials in the mid-South try to contain crop damage from the weedkiller sprayed on cotton and soybeans. Widespread reports of damage have left some growers feeling forced into buying dicamba-tolerant GE seed because other, non-tolerant varieties suffer when the chemical drifts onto them from nearby fields.
Following hundreds of complaints of damage, Arkansas recently banned the use of dicamba on row crops for the rest of the growing season. As of Tuesday, the state plant board had logged 633 complaints. In Tennessee, the Agriculture Department prohibited the use of older formulations of dicamba, which are more likely to drift, and, like Missouri, said the weedkiller can be applied only during the day.
Complaints about dicamba damage have skyrocketed this year despite the EPA’s approval of versions of the chemical that are less volatile and less likely to drift from the site of application. Growers use the herbicide in combination with new GE strains of soybeans and cotton to combat invasive weeds that are developing resistance to other weedkillers. Last year, crop damage was often attributed to the improper use of older formulations of dicamba that are more likely to drift in the wind.
“Stewardship is a shared responsibility,” said Missouri Soybean Association president Matt McCrate last week when state officials temporarily blocked the use of dicamba. He said he had heard “a steady stream of growers’ frustrations in recent weeks around dicamba—specifically [temperature] inversions, suspected off-label use, and drift, as well as feeling the need to invest in technology you might not otherwise choose as a type of insurance policy against damage.”
Missouri agriculture director Chris Chinn said three dicamba makers—BASF, Monsanto, and DuPont—“came to the table and agreed to additional safeguards for product use in response to issues we’ve faced this growing season.” Under the state’s new rules, one formulation of dicamba from each of the chemical companies can be used on dicamba-tolerant soybeans and cotton. Dicamba applications must be made between 9 a.m. and 3 p.m. and only when winds are below 10 mph.
Those are more stringent rules than usually applied to dicamba. A BASF circular, for example, says dicamba can be applied in winds up to 15 mph as long as the wind is not blowing toward sensitive crops. BASF also recommends creating a buffer around sprayed fields, keeping sprayer booms close to the ground, and using a special sprayer nozzle.
Successful Farming magazine said there were 140 complaints of dicamba damage in Missouri, 77 in Tennessee, and 55 in Mississippi.
University of Missouri weed specialist Kevin Bradley told the magazine that one-fifth of the soybeans in the Missouri “bootheel” have been damaged by dicamba. The extensive damage suggests difficulty in integrating dicamba-tolerant seeds into areas where farmers plant seeds with no resistance to the weedkiller, he said. “It will take a combination of [label] amendments for this technology to survive in the marketplace.”
Monsanto said it sympathized with farmers who experienced crop damage but suggested that dicamba may not be the culprit. On the company’s website, research chemist Alison MacInnes said she was part of a team that spent seven years developing and winning EPA approval of a dicamba formula that “provides a 90 percent reduction in volatility potential compared to” an earlier version. Dicamba has been used as a weedkiller for half a century.