CORESTA Congress, Kunming, 2018, Agronomy/Phytopathology Groups, AP 21

Quantifying dicamba residue in contaminated sprayers

North Carolina State University, Department of Crop & Soil Sciences, Raleigh, NC, U.S.A.

The deregulation of dicamba-tolerant cotton and soybean has increased the potential for dicamba exposure to tobacco through drift or tank contamination. Improper cleaning of sprayer equipment and off-target dicamba exposure can have detrimental consequences to the crop and future marketing opportunities. The objectives of this study are to document the contamination potential of dicamba residues in a spray tank after using a standard rinsing procedure and to evaluate response of flue-cured tobacco when treated with contamination rates.

Two and a half gallon polyethylene vessels, similar to a commercial spray tank, were used to simulate various tank cleaning scenarios. A “triple rinse” cleanout method was used as a standard cleaning procedure. Water only, a commercial cleaner, and ammonia were evaluated, along with a no cleanout treatment. Each formulation was replicated three times across two separate runs.

Spray vessels were contaminated with 1X rate of dicamba; simulating a use rate to that applied to dicamba-tolerant soybean or cotton. The tanks then underwent a triple rinse cleanout, adding the cleaner on the second rinse cycle. Rinse volumes were 10 % of the 1X mix size (2 gallon). A 20 mL sample of each rinsate was collected from each rinse within each cleaner and analyzed via HPLC to determine herbicide concentrations. Once the triple rinse procedure was completed, the vessel was again filled with water representing follow-up tank use and another sample was collected.

No difference was observed when a three-rinse method was used; regardless of cleaning agent (water, tank cleaner, and ammonia). Measurable differences were observed across the number of rinses. Recovered amounts after triple rinsing procedure could still cause visual injury and yield reduction.