AERIAL APPLICATION RESEARCH FOR EFFICIENT CROP PRODUCTION
Location: Areawide Pest Management Research
Title: Evaluation of spray drift using low speed wind tunnel measurements and dispersion modeling
Submitted to: Journal of ASTM International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 19, 2010
Publication Date: June 22, 2010
Citation: Fritz, B.K., Hoffmann, W.C., Birchfield, N., Ellenberger, J., Kahn, F., Bagley, W.E., Thornburg, J.W., Hewitt, A. 2010. Evaluation of spray drift using low speed wind tunnel measurements and dispersion modeling. Journal of ASTM International. 7(6):JAI102775.
Interpretive Summary: Drift associated with spray application of crop production and protection products is a continual concern for the potential detrimental effects to the environment and other neighboring cropland. As such, an increasing number of drift-reducing technologies are being developed and marketed for use with agricultural chemicals. With this growing market, there is a need to scientifically quantify and rate the effectiveness of these products in order to inform end users. In cooperation with the Environmental Protection Agency, data measured using established protocols were analyzed using available drift models to determine the applicability and feasibility of the evaluation protocols and a drift rating system to characterize drift reduction technologies. As a result of this work, a number of improvements to the established testing and rating methodologies were suggested in order to provide a science-based program that appropriately credits applicators for reduced drift with the use of effective technologies.
The objective of this work was to evaluate the EPA’s proposed Test Plan for the validation testing of pesticide spray drift reduction technologies (DRTs) for row and field crops, focusing on the evaluation of ground application systems using the low-speed wind tunnel protocols and processing the data using dispersion modeling. The measure of relative drift reduction potential for a given DRT tested in a low-speed wind tunnel is derived from airborne droplet size distribution measurements and airborne and deposited liquid volume measurements downwind from the spray nozzle. Measurements of droplet size and deposition data were made in a low-speed wind tunnel using reference nozzles included in the American Society of Agricultural and Biological Engineers (ASABE) standard for droplet size classification. The spray was comprised of a blank emulsifiable concentration (EC) spray mix which was applied at two different wind speeds. The WTDISP (Wind Tunnel DISPersion) model was used to evaluate the drift potentials of each spray. The wind tunnel measured data were in the form of droplet size and spray flux at six heights 2 m downwind of the spray nozzles, which was input into the WTDISP model. The specific objectives were 1) Evaluation of model accuracy by comparison of modeled downwind deposition to that measured in the wind tunnel; 2) Evaluation of drift reduction potential of the spray nozzles relative to a reference nozzle; and 3) Determination of low-speed wind tunnel data collection requirements for model input to optimize the evaluation process. The modeled deposition did not compare well to that measured in the wind tunnel, but this was expected as the model was not meant to be used for this purpose. The tested nozzles were rated using the International Standards Organization (ISO) drift classification standard. The drift ratings generally showed trends of larger droplet producing nozzles having greater drift reduction ratings. Examination of several scenarios using reduced model input requirements which would decrease the low-speed wind tunnel data collection time, did not show any conclusive results. The suggest that further testing and refinement of the data collection process and the WTDISP model may support wider use of this system for assessment of drift reduction technologies.