15 Factors for 2019 Dicamba Applications
Wondering how to manage dicamba in dicamba-tolerant soybeans this spring and summer?
Here are 15 highlights of what four Extension weed specialists – Aaron Hager with the University of Illinois, Bill Johnson at Purdue University, Mark Loux at Ohio State University, and Joe Ikley at North Dakota State University – are recommending for dicamba-based products based on EPA-approved revised labels for 2019 and 2020.
1 Use only approved dicamba formulations on (dicamba-tolerant) Roundup Ready 2 Xtend soybeans.
These formulations are:
- Xtendimax (Bayer Crop Science)
- FeXapan (same formulation as Xtendimax, but sold by Corteva Agriscience)
- Engenia (BASF)
2 Know that 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 operate under the supervision of someone with a license.
The labels again require applicators to attend an annual dicamba or group 4 herbicide-specific training prior to using the products.
3 Be aware that wind direction restrictions and buffer requirements have been revised.
The revised labels require:
- A buffer if wind is blowing toward a sensitive area.
- Dicamba cannot 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 of the target field, common sense would suggest it might not be advisable 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 omnidirectional 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 shows even the new dicamba formulations can volatilize for up to three days following application. Wind directions can change on day two or day three and move volatilized dicamba 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.
Thus, many spray applications occurred during days when average wind speeds were less than 10 mph but when wind gusts exceeded 10 mph. The specialists recommend not applying on days when wind gusts exceed 10 mph, even if sustained wind speeds fall below 10 mph. It’s not always easy to find a window with these lower wind speeds.
The reality is that some years can be challenging for making dicamba applications that have strict label precautions with regard to wind. It is impossible to predict when a gust of this magnitude will happen or how long it will last. Gusts that reach 30 mph can move spray particles and vapor for great distances.
5 Remember that time-of-day applications have changed.
Labels now allow applications to occur between one hour after sunrise and two hours before sunset. This restricts 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 something similar to determine whether or not a temperature inversion exists. . While these apps are not perfect in predicting the presence of an inversion, they can be better than a best guess. 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. For many tank-mix options, 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. 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 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.
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 neighboring Xtend fields have 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 Remember that dicamba is a tool for managing herbicide-resistant weed 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 spur development of dicamba-resistant weeds.