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Best Management Practices to Mitigate Dicamba Drift

By Larry Steckel, University of Tennessee Extension Weed Specialist 

We clearly have to get a better handle on the dicamba drift issue in this state. In cotton there is no reason to use anything but Liberty now. In soybeans, particularly seed fields, there may be no choice but to have to use a dicamba product.

The following are some best management practices to reduce the potential of off-target wandering of dicamba.

Avoid spraying in a temperature inversion. This one is much easier said than done and could be a major reason we have not been able to steward dicamba applications. What weather data I have seen is that West Tennessee experiences temperature inversions most every day in the months of June and July. The temperature inversions can start as early as 3:30 in the afternoon and run until 8:00 the next morning.

So what is an inversion? Typically, air temperature is warmest near the ground and colder at higher elevations. In an inversion, the opposite occurs, and the temperature of the air column flips. The colder air is near the soil and warmer air higher up. In an inversion, tiny spray droplets will hang in that cooler air for hours and often all night. In that time between when they are sprayed and when the spray droplets actually hit vegetation, these minuscule particles can move quite a distance off target.

You have all seen a temperature inversion perhaps without knowing it. In the fall when you cut soybeans of an evening and dust hangs in the air, that is a good sign of a temperature inversion. Other signs of an inversion are fog and heavy dew on the leaves. There is only one way to mitigate drift during a temperature inversion, and that is to avoid spraying when one is occurring. Anytime in the late afternoon and particularly the evening when winds get calm, a temperature inversion is likely occurring in June and July.

Some often think that dicamba drift due to inversions is the same as dicamba drift due to volatility. That is not correct. Any formulation can drift if sprayed during a temperature inversion, including Engenia and XtendiMax. Drift during an inversion is actually more similar to drift in a heavy wind where spray droplets physically move off target. Drift due to volatility is when the spray droplets hit the target, only to hours later lift back up into the air, not as a liquid droplet but as a gas. Only the older formulations of dicamba like Sterling Blue and Banvel are most prone to move off target this way.

Only use Engenia or XtendiMax. The older dicamba formulations are very likely to dry on the leaf and then depart the field hours later as a gas.

Only tankmix Engenia or XtendiMax with labeled products. Remember, everything that is added in the tank with Engenia or XtendiMax not only affects its efficacy on pigweed but also the size of the droplets that leave the spray tip as well as how prone to volatility the dicamba formulation is.

Use only labeled nozzles for the use of Engenia or XtendiMax. Do not use flat fan nozzles or other nozzles not on the label. In our research, with a dicamba herbicide, we have never gotten better pigweed control with spray tips like flat fan nozzles. However, we always greatly increase drift potential with those tips that produce a high percentage of very small droplets. Those tiny droplets can go a long way in the wind and even a much further distance if sprayed into a temperature inversion.

Keep the boom low. This one is also easier said than done but is critical to mitigate drift. The higher the boom, the more time the spray droplet is in the air and the more distance it can move with wind.

Finally, communicate with your neighbors and mind the spray buffers. It only takes a few folks not following the label to make all in production agriculture look bad.

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