Don't Dismiss Volatility

Tips to help reduce off-target dicamba movement.

Off-target dicamba movement affected millions of soybean acres in the U.S. in 2017, Image by Pamela Smith

There is no easy button for dicamba applications. Nearly every step connected with spraying XtendiMax, FeXapan and Engenia herbicides in the Roundup Ready 2 Xtend trait system has been tightened for 2018.

However, university weed scientists are also urging applicators to take additional actions to address volatility. “Applicators can do everything ‘per the label’ and still have off-site movement,” warns University of Illinois weed scientist Aaron Hager. “The new formulations may be lower in volatility, but that does not mean no volatility.”

In a collaboration between Ohio State University, Purdue University and University of Illinois, weed scientists say dicamba herbicides can move in the air or become attached to dust particles after application. Fine spray particles can also remain suspended in temperature inversions, and dicamba can move with runoff water after heavy rains.

In October 2017, the EPA responded to 2017 dicamba injury complaints by making the three herbicides restricted-use pesticides. Revised labels tack on training and recordkeeping responsibilities. They include more stringent restrictions on wind speed, wind direction and buffer zones. Those steps, and others like correct nozzles and adequate spray volumes, are important to reduce the risk of physical drift (droplets leaving the sprayer at the time of application) onto nearby sensitive crops.

Consider these suggestions from Ohio, Indiana and Illinois weed scientists to factor physical drift and volatility concerns:

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1. Watch The Wind. Don’t spray when the forecast indicates wind gusts will exceed 10 mph. In 2017, too many applicators focused on average wind speed and did not factor in gusts.

2. Lower The Boom. A 24-inch boom height limit is specified on the label. Reducing boom height from 48 inches to 24 inches can reduce the distance particles travel by 50%. Slow down to avoid running the boom into the ground--the label stipulates a speed limit of 15 mph and recommends 5 mph around field edges.

3. Build A Buffer. Last year, many applicators decided to apply dicamba right next to the sensitive crop if the wind was blowing the opposite direction. However, wind directions change, and University research shows even the new formulations can volatilize and move for up to three days following application.

4. Take Temperature Readings. Avoid applications when temperatures exceed 80ºF. Warmer temperatures increase the likelihood the herbicide will become more volatile.

5. Apply Early Season. Consider applying dicamba preplant, preemergence or very early postemergence when temperatures are more likely lower. Early-spring applications are less likely to cause injury even where dicamba moves since there’s less-developed vegetation.

6. Spray By Day. Labels are set between 3 and 10 mph during day hours to avoid temperature inversions--situations where small spray droplets remain suspended in the air. Droplets move when wind speed increases later in the day. Some states have set specific spray hours.

7. Adjust Additives. Never add anything to the tank that is not specifically approved on the product website. Avoid adding anything containing ammonium sulfate, which converts dicamba to more volatile forms. There are approved nonammonium sulfate-based water conditioners to reduce hard water antagonizing glyphosate that is tank-mixed with an approved dicamba formulation.

8. Know The Neighborhood. Have conversations with neighbors to know what crops and technologies are being planted around Xtend soybean fields. Applicators are required by label to show they surveyed the surrounding area.

Monitor these websites for label changes:




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