48th TWC, Tob. Work. Conf., 2018, abstr. 23

Simulated sprayer tank contamination with Dicamba

North Carolina State University, Raleigh NC USA

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. Synthetic auxin herbicides like dicamba are difficult to clean from spray equipment as these compounds readily adhere to plastic and rubber parts. Common herbicides such as glyphosate, are very efficient at dissolving dicamba residues from the inside of spray equipment. Subsequent use of sprayer tanks in tobacco is critical in preventing off-target movement when using across multiple crops. The objective of this study is to document the contamination potential of dicamba residues after multiple cleaning rinses. A triple rinse cleanout method was used for a standard comparing water, a commercial cleaner, and ammonia. The cleaner and ammonia were added on the second rinse. Polyethylene (2.5 gallon) vessels were contaminated with dicamba (at a labeled rate) to simulate a sprayer tank. Rinse volumes were 10% of the tank’s volume. During each rinse, a 20mL sample was collected for analysis. Once the vessel was cleaned using the triple rinse procedure, it was filled again and another sample was collected; representing subsequent tank use. Samples collected during each rinse were analyzed using high-performance chromatography-mass spectrometry (HPLC-MS). Data reveal a significant decrease in recovered dicamba residues with increasing number of rinses. No difference was noted for rinsate collected from the 3rd rinse and rinsate from the subsequent fill-up. No difference in cleaning efficiency was observed with the commercial tank cleaner and ammonia compared to water alone. There was approximately an 80% reduction in dicamba concentrations with the first two rinses. After three rinses, 0.4% of the original mix rate was recovered from the tank. Based on previous research, this amount is enough to cause a yield reduction and visual injury to flue-cured tobacco. (Reprinted with permission)