Monsanto proudly says its low-volatility formulations of dicamba, coupled with cotton and soybean varieties genetically modified to tolerate doses of the herbicide, are an effective tool against invasive weeds. But weed scientists report that damage to neighboring fields and susceptible nearby crops is a recurring problem this year.
“I have never seen a herbicide that has so easily and frequently slipped the leash,” wrote Tennessee weed scientist Larry Steckel in Delta Farm Press. Bob Hartzler, a weed specialist at Iowa State University, said there was “near unanimous agreement that the level of off-target injury observed in 2018 is unacceptable” among university weed scientists during recent teleconferences with the EPA. The regulatory agency, which tightened the rules on use of dicamba for this growing season, is expected to announce any modifications on the weedkiller well before the 2019 planting season.
An estimated 4 percent of soybeans nationwide were damaged to some extent by dicamba last year. A reliable figure is not yet available this year. Hartzler said ISU extension agronomists generally believed damage this year was comparable to 2017 and they all agreed that volatility, when the chemical evaporates from where it was sprayed and moves cloud-like across the land, was the issue behind some of the complaints of pesticide “drift.”
“This is the third year where there have been major issues keeping dicamba in the field but Palmer amaranth control was good in the fields where it was applied,” wrote Steckel, referring to an invasive weed. Usually, drift occurs during spraying and the droplets travel a short distance. “Dicamba drift for the past three years has often traveled a half mile to three-quarters of a mile and, all too frequently, well beyond that.” Some growers said they switched to dicamba-tolerant varieties because of damage in previous years.
Monsanto said in mid-July that soybean growers “reported 97 percent weed control satisfaction” with its low-volatility versions of dicamba. “This season, we have good order strength, and U.S. farmers are on track to plant nearly 50 million acres of dicamba-tolerant soy and cotton, more than doubling last year’s figures.”
Beck’s Hybrids and Stine Seed, the two largest independent U.S. seed companies, told Reuters that they want the EPA to ban use of dicamba on row crops during the summer. Arkansas, the epicenter of dicamba damage last year, banned use of the herbicide on cotton and soybeans throughout the 2018 growing season. “Anybody that sprays it, you have issues with the volatilization,” said Beck’s Chief Executive Sonny Beck.
Steckel and Beck voiced the same concern, that problems with dicamba could tarnish the reputation of farmers as good stewards. Monsanto has blamed improper use or application of dicamba for complaints of damage to neighboring crops. Hartzler said weed scientists gave EPA some ideas for dicamba going forward. They included temperature and date cut-offs for application of dicamba, buffers on all sides of the field, not just downwind, and clarification of sensitive crops.
“Off-target movement of dicamba is complex, there is no simple solution, and whatever action the EPA takes will not make everyone happy,” said Hartzler.