Moving Forward with Dicamba

November 14, 2018
ICM News

On October 31, 2018, the EPA made the long-awaited announcement regarding dicamba registration for use on dicamba-resistant soybean. I suspect opinions regarding the EPA actions are as varied as people’s views of the technology. Following are pertinent changes on the dicamba labels:

  1. People under the supervision of a certified applicator are no longer allowed to make applications.
  2. Applications are allowed only from 1 hour after sunrise to 2 hours before sunset (previously the restriction was between sunrise and sunset).
  3. Applications are restricted to 45 days after planting or prior to R1 stage of soybean, whichever comes first (previously the restriction was up to and including the R1 stage).
  4. Applications cannot be made if rain within 24 hours may result in soil runoff (previously the label stated not to apply if rain is expected to occur within 24 hours).
  5. The label clarifies what constitutes sensitive areas and where downwind buffers are required. The applicator must survey the area for sensitive crops and residential areas, and then not apply the product when wind is blowing towards these areas. It is up to the applicator to determine the appropriate distance between the target site and sensitive area. One of the more important changes is that the label states that managed or mowed areas adjacent to fields are now considered a non-sensitive area. Thus, the road right-of-way can be considered part of the 110 ft downwind buffer.
  6. There is a new restriction regarding buffers around the entire field in counties with endangered species. The specifics have not been posted at this time, but this probably won’t impact applications in most of Iowa. EPA has a website identified on the label that will have bulletins related to this restriction.
  7. Dicamba specific training will again be required for all applicators using the registered products on dicamba-resistant soybean.

I still have reservations about the ability to use dicamba postemergence in soybean with an acceptable level of risk to sensitive vegetation (Table 1). Restrictions related to wind speed, rainfall, and hours during the day when applications are allowed, provide few hours that are appropriate (legal) for application. The label changes for 2019 do little to reduce the risk for volatility; experience indicates that volatilization has played a significant role in off-target movement and injury. Preemergence applications of dicamba greatly reduce the likelihood of injury compared to postemergence applications, and this is our recommendation for the technology. However, I recognize preemergence applications reduce the value of dicamba on weeds with prolonged emergence, such as waterhemp. The potential for off-target movement increases as postemergence applications are delayed. When using the new dicamba products postemergence, the goal should be to complete applications by the V2 – V3 stage of soybean. Avoiding applications when temperatures are forecast to exceed 85°F within 24 hours after application will reduce the potential for volatility losses. Combining dicamba with a Group 15 herbicide (Dual, Warrant, Zidua, etc.) when it is applied early postemergence will prolong activity on late-emerging waterhemp.

Table 1. Pesticide misuse cases handled by IDALS

Year

Total complaints

Total Group 4

Dicamba

2012

120

-

-

2013

122

-

-

2014

89

-

-

2015

108

-

-

2016

102

23

16

2017

211

131

117

2018 

231

129

57

The spread of multiple resistance weeds has greatly complicated weed management, creating the demand for new tools. Dicamba requires a much higher level of management than any other herbicide to be used safely. It is the applicator’s responsibility to follow all label requirements, and know what sensitive plants are in the vicinity of any Xtend field being sprayed with dicamba.

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Bob Hartzler Professor of Agronomy

Dr. Bob Hartzler is a professor of agronomy and an extension weed specialist. He conducts research on weed biology and how it impacts the efficacy of weed management programs in corn and soybean. Dr. Hartzler also teaches undergraduate classes in weed science and weed identificatio...