This spring marked the official launch of the Roundup Ready 2 Xtend® system which included new dicamba formulations (XtendiMax™, Engenia™, and FeXapan™) for over the top use in soybeans.  This was a much anticipated, and needed, tool throughout our geography to manage our tough-to-control and resistant weed species that plague much of the Midwest.  With any new technology, there is a learning curve that is required to provide successful stewardship while providing the desired weed control—and this technology is no different.

Earlier this year, there was temporary halt of dicamba applications in Arkansas along with the reevaluation of application protocols in Missouri and other states.  These cautionary responses have primarily been due to the reported off-target movement of dicamba during the application period.  To some degree or another, most Midwest states have seen some off-target movement of dicamba.  This off-target dicamba symptomology is most commonly characterized by cupping of new soybean trifoliates and parallel vein orientation on the underside of the soybean trifoliates.  The following are the four primary ways in which dicamba can move off-target.

Physical Drift
This is the movement of spray particles in the wind from intended target to an unintended area.  This is generally the easiest movement to spot as the area directly downwind is most affected and the injury lessens as the distance from the intended target increases.

Temperature Inversions
These occur when the air temperature at the surface of the earth is cooler than the air above it.  If applications are made during a temperature inversion, very small spray particles can remain suspended in the air and have the potential to move distances greater than 1 mile before being deposited into a susceptible area.

Tank Cleanout
Dicamba injury from incomplete tank cleanout can range from minor cosmetic injury to persistent leaf cupping that limits yield.  When the boom is still contaminated, the area where the sprayer started is typically more severely affected and the injury decreases as the sprayer makes it all the way around the perimeter of the field.  However, the whole field may appear cupped if there was enough contamination in the spray tank or tender.

Volatility
Herbicide volatility is more likely to occur during some key environmental conditions, such as high temperatures and low relative humidity, which cause susceptible herbicides to change from a liquid to gaseous state.  All commercially available dicamba formulations are susceptible to volatilization, but some older formulations are more prone than the newly registered products.

So now how do we limit the potential for off-target dicamba movement?  The key is to use our best management practices (BMPs) to ensure good stewardship.  This includes using the right nozzles, managing pressure at the spray tip, keeping the boom low, monitoring wind speeds, and utilizing a buffer to mitigate physical drift.  Not spraying during a temperature inversion helps reduce the risk of long distance herbicide movement.  Triple rinsing sprayers with a quality tank cleaner helps to minimize potential for contaminants to be present when we move to a dicamba-sensitive field.  Also, using an approved dicamba formulation and tank mix partners can reduce the risk of herbicide volatility.

Managing off-target movement is the key to long term success for this technology.  In areas where off-target movement has occurred, investigate the root cause and evaluate solutions to make future applications more successful.  This technology is a tool to help us manage our glyphosate-resistant weeds, including waterhemp, so proper stewardship is required to ensure that it is a viable option for many years to come.