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15 Factors for 2019 Dicamba Applications

EPA label changes impact buffer requirements and wind speed and time-of-day application windows.

Wondering how to manage dicamba in dicamba-tolerant soybeans in 2019? Here’s what four Extension and university weed specialists – Aaron Hager with the University of Illinois, Bill Johnson and Joe Ikley with Purdue University, and Mark Loux at Ohio State University – are recommending regarding dicamba in 2019. (Their complete recommendations can be found here.) 

1. Use only approved dicamba formulations on (dicamba-tolerant) Roundup Ready 2 Xtend soybeans.  

They are:

  • Xtendimax (Bayer)
  • FeXapan (same thing as Xtendimax, but sold by Corteva Agriscience)
  • Engenia (BASF)

The federal labels for these herbicides contain detailed application instructions to reduce risk of off-target movement. However, in 2017 and 2018, there were thousands of cases of off-target movement affecting millions of acres throughout the soybean-growing region of the U.S. In late October 2018, the EPA approved revised labels for Xtendimax, FeXapan, and Engenia for 2019 and 2020. 

2. All three products are restricted-use pesticides. This means an applicator’s license must be held in order to purchase and apply these products. It is no longer acceptable to simply operate under the supervision of someone with a license.

The labels continue to require applicators to attend an annual dicamba or group 4 herbicide-specific training prior to using the products. In addition to becoming restricted-use pesticides, these revised labels have more restrictions outlining how the products should be applied. 

3. Wind direction restrictions and buffer requirements have been revised. The revised labels require:

  • A buffer if wind is blowing toward a sensitive area.
  • Dicamba should not be applied at all if the wind is blowing toward a sensitive crop. 

In 2017 and 2018, it appeared that many applicators did not follow this restriction. This perhaps occurred because a specific distance to the sensitive crop was not specified and sensitive areas were not well defined. 

Realistically, if the sensitive crop is within ½ mile or less of the target field, common sense would suggest it might not be a good idea to apply to that field. If wind is blowing toward extremely sensitive vegetation – such as non-Xtend soybean varieties – don’t spray until the wind is blowing away from the sensitive crop on the day of application and also for the next two to three days after application.

These buffers are more restrictive for 2019. In addition to the downwind buffer to sensitive areas, there is now a 57-foot in-field buffer around the perimeter of fields if an endangered species is present in your county. Applicators must now check the appropriate sources for the presence of endangered species.

University research has demonstrated that even the new formulations of dicamba can volatilize and move on dust particles for up to three days following application. Wind directions can change on day two or day three and move volatilized dicamba or dicamba dust to sensitive vegetation. So, the establishment of buffers is extremely important if you are near a sensitive area.

4. Don’t overlook wind gusts. The new labels allow spray applications between 3 and 10 mph wind speeds at boom height. In 2017 and 2018, many applicators may have focused more attention on average wind speed rather than wind gust speed.

As a result, many spray applications were made during days when average wind speeds were less than 10 mph, but when wind gusts exceeded 10 mph. The specialists strongly recommend not applying on days when wind gusts exceed 10 mph, even if sustained wind speeds fall below 10 mph. It is not always easy to find a window with these lower wind speeds.

The reality is that some years can be challenging for making applications of dicamba products that have very strict label precautions with regard to wind. It is impossible to predict when a gust of this magnitude will happen nor how long it will last. Gusts that reach 30 mph can move spray particles and vapor for great distances.

5. Time-of-day applications have changed. The labels now allow applications to be made only between one hour after sunrise and two hours before sunset. This is to restrict applications to times when temperature inversions are less likely to occur.

If the time-of-day restriction was in place in 2018, there would have been substantially fewer hours in June where applications could be made. Accounting for conditions that allowed equipment traffic, west central Indiana would have had only 39 hours in June with wind speeds between 3 and 10 mph between the legal application hours. 

6. Use an app to detect temperature inversions. During a temperature inversion, small spray droplets remain suspended in the air and do not settle on plants or the soil surface. The specialists recommend that you use an app like Spray Smart or someting similar to determine whether or not a temperature inversion exists. If there is a temperature inversion, do not spray until the inversion has lifted.

7. Use approved nozzles. Consult company websites for the respective herbicides to find the list of approved nozzles and spray pressures.

8. Check company websites for approved spray additives and tank-mix partners. The list of approved spray additives changes frequently, so it is important to regularly check them. All approved dicamba products require the use of a drift-control agent from the list of approved drift-control agents on their respective website. Adding any other product, including a foliar fertilizer, insecticide, herbicide, or fungicide  that is not listed on the website for the respective herbicide constitutes a label violation.

Do not add ammonium sulfate or anything containing ammonium sulfate, as this produces more of the volatile form of dicamba.

Approved nonammonium sulfate-based water conditioners exist to reduce hard water antagonizing glyphosate that is tank-mixed with an approved dicamba formulation. Use of a pH buffer may be necessary to keep spray solution pH above 5. A pH below 5 can increase volatility of dicamba products. 

9. Reduce boom heights to 24 inches above the target height limit specified on the label. Simply reducing the boom height from 48 to 24 inches has been shown to reduce the distance traveled by drift particles by 50%.

10. Slice travel speed. One of the most effective ways to safely lower the boom height without running the boom into the ground is to reduce sprayer travel speed. Also remember that any travel speed over 15 mph is off label. The labels also now recommend that travel speeds be reduced to 5 mph when making applications on the field edges.

11. Avoid application when temperature exceeds 80°F. Assuming that these dicamba products have some potential for volatility, the risk of this occurring increases with temperature.

12. Consider applying dicamba only preplant, preemergence, or very early postemergence. Over 90% of the offsite movement complaints resulted from postemergence applications. Our assumption is that applications earlier in spring will have less likelihood to cause problems even where dicamba moves, due to the absence in many cases of any developed vegetation to injure. Temperatures are also likely to be lower when applied preplant/preemergence vs. postemergence, possibly reducing the risk of movement via volatility.

 13. Talk with neighbors to know what crops and technologies are being planted around Xtend soybean fields. Many offsite movement cases in 2018 occurred where neighbors planted Xtend and non-Xtend soybean adjacent to each other. Knowing which sensitive crops are in the vicinity of your Xtend fields will enable better decision-making about use of dicamba in a given field.

 14. Keep in mind that you can do everything per the label but still have offsite movement. This happens because: 

  • Even new dicamba formulations may volatilize and move on dust particles. 
  • Fine spray particles can remain suspended in inversions.
  • Dicamba can move with runoff water after heavy rainfall events.

15. Dicamba is a tool for managing herbicide-resistant populations, but it’s not foolproof. 

Selection for dicamba resistance occurs each time dicamba is applied. Just as with glyphosate, overreliance on this technology will lead to the development of dicamba-resistant weed populations. 

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