Wind tunnel and field evaluation of drift from aerial spray applications with multiple spray formulations

Authors: Fritz, Bradley - Brad; Hoffmann, Wesley; BRETTHAUER, SCOTT - University Of Illinois; WOLF, ROBERT - Wolf Consulting & Research Llc; BAGLEY, WILLIAM - Wilbur-Ellis Company

Submitted to: Journal of ASTM International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2012
Publication Date: 6/22/2012
Citation: Fritz, B.K., Hoffmann, W.C., Bretthauer, S., Wolf, R.E., Bagley, W.E. 2012. Wind tunnel and field evaluation of drift from aerial spray applications with multiple spray formulations. Journal of ASTM International. doi 10-1520/STP104403.

Interpretive Summary: Improving application efficiency and decreasing drift from aerially applied treatments requires knowledge of all spray system components, including impacts of active ingredients and spray adjuvants on spray droplet size. However, information about the influence of spray adjuvants on the generation of spray droplets is lacking for most active ingredient products. This work examined size, deposition, and drift of spray droplets under field conditions using a fungicide that has widespread market share in the aerial application industry and several commonly used spray adjuvants. Wind tunnel tests demonstrated that spray adjuvants had little impact on droplet size because of dominant airspeed shear effects. Modeling and field testing showed little difference in spray drift from active ingredient spray solutions with or without adjuvants. Although the interaction of active ingredient spray formulations and spray tank modifiers under aerial application conditions may not significantly influence droplet size, adjuvants that provide evaporation, penetration, sticking, or spreading control can potentially be used without detrimental impact on spray applications.

Technical Abstract: The impact of different spray tank modifiers into an active ingredient spray mixture on spray atomization and in-field behavior under aerial application conditions were examined. Wind tunnel tests demonstrated that active ingredient solutions potentially results in significantly different atomization characteristics from the typical water and non-ionic surfactant “blank” reference sprays used. The addition of spray adjuvants into the active ingredient spray formulation showed less impact on the resulting atomization properties with the polymers tested broadening the droplet size distribution and the oil concentrates having little impact. Through modeling, the droplet size data were translated into estimates of movement and fate under field conditions also demonstrating little difference between the active ingredient and adjuvant spray formulations. However, all treatments did show reductions in estimated drift levels as compared to a 11003 flat fan reference treatment. The modeling results also demonstrated that the relative drift reduction levels are highly dependent on the wind speed under which the applications take place. The field evaluation highlighted the difficulty of comparing a large number of spray formulations or treatments even when every effort was made to minimize time between replications. These results have led the authors to conclude that field testing of potential DRTs under aerial application conditions will be cost prohibitive and likely would give highly variable results. Wind tunnel evaluations at certified laboratories offer a much quicker and inexpensive method for evaluating large numbers of nozzle and spray formulation treatments. Overall the results of this study highlight the need to further investigate the interaction of active ingredient spray formulations and spray tank modifiers under high speed air shear atomization conditions to better understand the potential role and benefit that adjuvants play in aerial applications.