Among the few areas of consensus regarding over-the-top dicamba applications on herbicide-tolerant soybeans are that the system provided excellent weed control and no one wants to see a repeat of the off-target damage that occurred in the technology’s first year of commercialization in 2017.

Herbicide manufacturers main­­tain that additional training and education will solve the problem of off-target dicamba damage, which affected an estimated 3.3 million soybean acres across the United States last year.

“We believe training is the key fundamental aspect in assuring the success of this technology,” Boyd Carey, Monsanto regional agronomy lead, told farmers at the American Farm Bureau Federation annual convention in Nashville earlier this month. The stakes are high.

The Environmental Protection Agency (EPA) set the registrations for over-the-top dicamba applications on soybeans to expire in two years to allow the agency to change or revoke the registration if necessary.

At a crossroads

That makes 2018 a critical year. The EPA already took the unusual step of reclassifying the three new dicamba formulations approved for over-the-top use on soybeans as restricted use pesticides. As such, farmers and commercial applicators who want to apply those herbicides must undergo additional training and follow stricter record-keeping requirements.

“We’re at a crossroads,” said BASF technical service representative Greg Stapleton. “You’ve got to follow the letter of the law. If we don’t, and we have the problems we had last year, we’re just not going to have this technology.”

The new rules apply only to Monsanto’s Xtendimax with VaporGrip Techology (VGT), BASF’s Engenia and DuPont’s FeXapan with VGT, which are the only three dicamba formulations approved for in-season use on Roundup Ready 2 Xtend dicamba-tolerant soybeans.

More than 30 dicamba applicator training sessions, conducted by Monsanto and BASF officials, have been scheduled in Iowa from now through late March. For a list of training seminars across the state, go to

Misuse complaints rise

Pesticide misuse complaints reported to the Iowa Department of Agriculture last year were more than double the number compared to previous years, said Iowa State University Extension weed scientist Bob Hartzler.

He estimates more than 90 percent of the 175 ag-related complaints were due to dicamba injury. Extension specialists estimate 150,000 soybean acres in Iowa suffered some level of dicamba injury in 2017.

The main ways that off-target dicamba damage occurs are particle drift, tank contamination and vapor drift (volatilization), Hartzler said. Researchers have also found occasions where the herbicide moved via wind erosion or runoff, he said.

He and other Midwest university weed scientists are skeptical whether the EPA’s label changes and training requirements will fully eliminate the problems experienced last year.

“Particle drift and tank contamination are fully under the operator’s control,” said Hartzler. “The other routes of movement … you can do everything right and still have problems.”

He said the new low-volatility dicamba formulations work well in a controlled setting, but a number of factors can cause off-target movement in real-world situations, Hartlzer said.

The timing of in-season applications on soybeans amplify the risks, since it takes very little dicamba to injury sensitive crops, Hartzler said.

As little as 3 milliliters of dicamba in a 1,000 gallon sprayer tank is enough to cause visible injury in sensitive crops, said BASF’s Stapleton. It’s critical to fully clean out sprayer tanks as well as storage tanks, pumps and hoses used when mixing herbicides, he said.

Applicators must also maintain a 110-foot downwind buffer, use correct nozzle types and may only spray dicamba over-the-top on soybeans during daylight hours when the wind is blowing between 3 and 10 miles per hour.  

The right environmental conditions can be tough to find in Iowa in the spring, Hartlzer said. After looking at four years of weather data for the last week of May in central Iowa, he found conditions were unsuitable to meet the new label requirements on four out of seven days. Additionally, there was just a 90-minute window to spray on two other days.

“I just look at it and say how in the world can we apply this product legally? I just don’t see how we can get the acres covered,” said Hartlzer.

Hartzler and ISU Extension colleague Mike Owen are recommending only pre-emergence applications of dicamba on soybean acres.

BASF’s Stapleton said misapplication errors can be minimized by strictly following the label and being flexible if sensitive crops are planted in adjacent fields. That may mean not spraying dicamba on Xtend soybeans in certain situations.

“Keeping this stuff on-target is important,” he said. “We need to protect our neighbors. Not every field should be sprayed with dicamba.”