Drift Control Adjuvant Benchmarking in Agricultural Spray Applications

Drifting of fine droplets during the application of pesticides is an issue of increasing commercial and regulatory importance. Spray drift damages susceptible crops, wastes resources, and results in inconsistent weed control. Several strategies are currently used to mitigate this problem. These include enhanced nozzle technology, improved application techniques, and inclusion of drift control additives in the final tank mix. Elimination of small diameter droplets (“driftable fines”) is a key goal. Measurements were made of droplet size distributions of sprayed pesticide formulations containing commercial products representative of the leading drift control technologies, including guar, polyacrylamides, lecithin, and oil/surfactant mixtures. Effects of spray nozzle and pressure were also evaluated. Nozzle technology plays a large role in determining the spray droplet size spectrum. However, there is a strong interplay between nozzle design and formulation variables. We found that drift control agents have greater impact on spray from flat fan nozzles. Also, the ranking of adjuvants depends on the nozzle technology in use: for glyphosate/ammonium sulfate solutions, polymers were more effective in reducing fines from a flat fan nozzle, while surfactant-based products were marginally superior when an air induction nozzle was used. The regulatory community is currently focused on mitigating the generation of small droplets. However, the generation of oversized droplets also effects spray efficacy. The impact of drift control agents on the breadth of the droplet size spectrum is an aspect of drift control which is often overlooked. We found that emulsion-based products tighten the droplet size distribution, while the polymer-based products shift the mean droplet diameter up, broadening the distribution in the process: while the latter effect may earn better ratings from regulatory agencies concerned exclusively with spray drift mitigation, it may be less helpful in enhancing application efficacy.