Off-target movement of pesticides can be due to spray drift, volatility of the active ingredient (AI), or both. It is often difficult to assess the cause of the off-target movement of the AI in the field. Utilizing Battelle’s Agricultural Drift Tunnel (AgDT), various herbicide treatments of dicamba can be quickly and economically tested to determine the impact of spray drift and volatility on the overall off-target movement of dicamba. By adding a metal tracer in the form of a salt, in this case cesium chloride, the amount of off-target movement can be attributed to either spray drift or volatility based on the ratio of dicamba-to-metal. If there was no volatility of the AI, then the ratio of the metal-to-AI collected on the PUF samplers would be identical to the ratio of metal-to-AI in the tank mix. To determine the accuracy of the metal tracer method, topsoil was applied with 0.5 lb acid equivalent per acre using a six-nozzle boom equipped with either TeeJet XR11001 or TTI11001 nozzles at 40 PSI. The assembly traversed the application area at a speed of 2 mph which yielded an overall application rate of 15 GPA. Tunnel wind speed was maintained at a constant 10 mph during the application, then reduced to 5 mph over the remainder of the 24-hour test period. Filter papers were pinned to cardboard and attached to 3-inch riser blocks for ground deposition sampling. Vacuum pump driven PUF (polyurethane foam) samplers were co-located to each of the ground samplers at a height of 1-foot above ground to capture volatility. Six replicate samplers were placed 4, 8, 16, and 30.5 m downwind from the traversing boom. Deposition filter papers were collected 2 minutes after the spray application, while PUFs were collected 24-hours after application. Three tank mix solutions containing PowerMax (glyphosate) or Liberty (glufosinate) were paired with FeXapan (dicamba). All samples were analyzed via LC-MS for dicamba and ICP-MS for cesium. The resulting analysis will provide an overview of how a metal tracer can be used to determine the cause off-target movement.

Determining spray drift vs volatility utilizing a metal tracer

ACS Fall 2021

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