Dicamba Impacts for 2018

New label imposes additional requirements 

Changes to dicamba herbicide labels will affect how you use the technology in the coming season.  

The changes include restrictions on who is permitted to apply these herbicide formulations in 2018 and when spraying is allowed. The new requirements by the U.S. Environmental Protection Agency are a response to widespread plant injuries in 2017 caused by off-target movement of the herbicide. Among the federal label changes: 

  • XtendiMax, Engenia and FeXapan are now classified as “restricted use” products. Only certified applicators with special dicamba training will be allowed to apply these products in 2018. 
  • Maximum allowable wind speeds for application have been reduced from 15 mph to 10 mph. 
  • Applications are limited to between sunrise and sunset.
  • Additional records are required to document applications and sprayer system cleanouts. 
  • New language highlights the risks to nearby sensitive crops from physical movement of the herbicide due to application drift or particle movement during temperature inversions. 
  • Individual states have imposed additional restrictions on dicamba applications in 2018.  

How will these label changes affect you next season? Here are a few things to keep in mind when making decisions about whether dicamba technology is right for your farm: 

  • Off-target movement remains a risk.“Historically, dicamba has always been a challenging herbicide to keep in place,” says Jeff Gunsolus, University of Minnesota Extension weed scientist. New formulations are less volatile than older formulations, he says. “However, reduced volatility does not mean no volatility,” he adds.  

Even a small amount of volatility — combined with the extreme sensitivity to dicamba from susceptible soybeans and other crops — makes off-target damage a considerable risk, Gunsolus says. On top of that, reporting crop damage from off-target movement presents a dilemma for farm neighbors due to the risk of damaging personal relationships, he adds. 

  • Fewer hours will be available for application, and suitable field days may not coincide with the need to apply the herbicide. Bob Hartzler, Iowa State University weed scientist, analyzed four years of weather records for Boone, Iowa, to estimate how many hours would likely be available to spray dicamba under the new label. In late May, half of the days were totally lost for spraying due to wind and rain restrictions. In June, daily temperatures exceeded 85 degrees during 22 of 28 days, increasing the potential for vapor drift.  

A 2017 analysis by Purdue University weed scientists came up with similar findings. The report states that in a wet year like Indiana experienced in 2017, “It would have been extremely challenging to spray the approved dicamba products in June, when many postemergence herbicide applications were needed.”  

  • Label requirements are difficult to implement in the field. “This label is one of the most detailed, yet challenging, labels to implement under the varying field and environmental conditions commonly experienced in a growing season,” Gunsolus says. Commercial and farmer applicators generally said they put forth their best effort to apply the new dicamba formulations properly in 2017, he says. Yet crop injuries were common. 
  • You have other options for managing resistant weeds.Farmers battling multi-herbicide-resistant weeds in soybeans and cotton often say they desperately need dicamba technology, Gunsolus says. But there are alternatives. Since there are no reports of broadleaf weeds resistant to the herbicide glufosinate, LibertyLink technology could be considered. Another option is to rotate to a crop in which resistant weeds are easier to control.  

As growers finalize plans for 2018, Gunsolus urges them to step back and consider the original impetus for the dicamba-use changes: weed resistance to multiple groups of herbicides. “Herbicides alone cannot adequately manage herbicide-resistant weeds,” he says. “Integration with mechanical and cultural weed control is essential.” 


Photo Credit: © iStock PBouman 2017

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