Among the few areas of agreement regarding application of the new dicamba herbicides on dicamba-tolerant soybeans is that the system provided excellent weed control in 2017 — the first year on the market for these products — and no one wants to see a repeat of the off-target damage that occurred.

Preventing dicamba drift to non-dicamba-tolerant soybeans has been the focus of training meetings for farmers and commercial applicators this winter.

More than 30 meetings were held across Iowa by BASF, DuPont Pioneer and Monsanto. The training is required for anyone who plans to apply BASF’s Engenia, DuPont’s FeXapan and Monsanto’s XtendiMax with Vapor Grip Technology this year.

The training sessions focus on compliance with the product label, application requirements, required record keeping, susceptible and sensitive crops, window of application, and weather conditions, such as temperature inversions. The meetings last 90 minutes, and participants receive a certificate of completion.

“As we prepare for the 2017 application season, we are reminding growers and applicators that with the new federal label, training is mandatory for all applicators this year,” says Ryan Rubischko, Monsanto’s dicamba lead. “We believe training and education are the key fundamental aspects in ensuring success of this technology.”

Dicamba at crossroads
The stakes are high. The Environmental Protection Agency set the registrations for postemergence dicamba application on dicamba-resistant soybeans to expire in two years to allow the agency to change or revoke the registration if necessary.

Thus, 2018 is a critical year. “We are at a crossroads,” says BASF technical service representative Mark Storr, based in central Iowa. “The registration for these products expires in November. If we see a repeat of 2017, with widespread off-label use, there’s a high probability this technology will go away.”

Losing the dicamba option would be tough for farmers dealing with a dwindling number of herbicides trying to control an increasing number of resistant weeds.

Proper use is important to keeping herbicide products on the market, says Ed Anderson, director of research for the Iowa Soybean Association. Even small deviations can lead to major issues for farmers and their neighbors.

New tools needed to fight weeds
“Farmers need integrated approaches to combat weeds,” Anderson says.

“Herbicide-resistant weeds are a risk,” he adds. “Appropriate evaluation and use of the dicamba system, combined with other innovative technologies and management practices, are essential to control evolving weed populations.”

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

He estimates over 60% of the 200-plus ag complaints were due to dicamba injury. Hartzler and ISU’s Mike Owen surveyed ISU Extension field agronomists and estimate 150,000 soybean acres in Iowa suffered some level of dicamba injury in 2017.

Off-target dicamba damage can occur several ways. Particle drift, sprayer tank contamination, and vapor drift or volatilization are the main causes, Hartzler says. He and Owen, along with other Midwest university weed scientists, are skeptical of whether EPA’s label changes and training requirements will fully eliminate the problem experienced last year.

“Particle drift and tank contamination can be controlled by the operator,” Hartzler says. “The other ways dicamba can move off-target, such as volatilization, aren’t easily controlled. You can do everything right and still have problems.”

“My contention is that due to the label changes, it is nearly impossible for applicators to use the new dicamba products legally,” says weed scientist Bob Hartzler.

The new low-volatile dicamba formulations work well in a controlled setting, but several factors can cause off-target movement in field situations.

The timing of applications on soybeans increases the risk, as it takes minute amounts of dicamba in the drift to injure sensitive crops. As little as 3 milliliters of dicamba in a 1,000-gallon sprayer tank is enough to cause visible injury to non-dicamba-tolerant soybeans. It’s critical to clean out tanks, pumps and hoses before spraying other herbicides.

Going with post application
Applicators must also maintain a 110-foot downwind buffer (see story on previous page), use correct nozzle types and only spray dicamba postemergence on soybeans during daylight hours when the wind is blowing between 3 and 10 miles per hour.

"The right environmental conditions to spray dicamba can be difficult to find in Iowa in the spring,” Hartzler says.

After studying four years of weather data for the last week of May in central Iowa, he found that conditions were unsuitable to meet the new label requirements on four out of seven days. And there was less than a five-hour window to spray on another day, leaving only two days with more than five hours to spray. Weather conditions are more favorable in June, but higher temperatures increase the risk of volatilization.

Limits create tough situation
“Looking at this situation, I wonder how in the world can we apply this product legally? I don’t see how we can get the acres covered in that short period,” Hartzler says. Thus, he and Owen are recommending only preemergence application of dicamba on soybean acres.

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 some situations.

“Keeping dicamba on target is important,” Storr says. “We must protect our neighbors. Not every field should be sprayed with dicamba.”