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Title: Effects of spray mixtures on droplet size under aerial application conditions and implications on drift

Author
item Fritz, Bradley - Brad
item Hoffmann, Wesley
item BAGLEY, BILL - Wilbur-Ellis Company

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2009
Publication Date: 2/18/2010
Citation: Fritz, B.K., Bagley, B., Hoffmann, W.C. 2010. Effects of spray mixtures on droplet size under aerial application conditions and implications on drift. Applied Engineering in Agriculture. 26:21-29.

Interpretive Summary: The use of simulated and mimic sprays for spray studies in high-speed wind tunnels allows researchers to limit the amount of active ingredients used in spray tests. However, it is important that these simulated and mimic sprays have the same physical characteristics of sprays containing active ingredients. Studies were conducted to compare a number of spray solutions for droplet size resulting from a range of airspeeds. The measured droplet size data were compared for potential off-target movement (drift) using a dispersion model. Generally, droplet size decreased and drift increased as airspeed increased. Significant differences were found between droplet size characteristics of the active ingredient and mimic spray formulations. Care should be taken when using mimic spray formulations in place of active ingredients, as the active ingredient significantly impacts the generation and drift potential of spray droplets created by aerial application technologies.

Technical Abstract: The use of simulated and mimic sprays for atomization studies in high speed wind tunnels allows researchers to limit the amount of active ingredients used in spray tests; however, it is important that these simulated and mimic sprays have the same physical and atomization characteristics of spray containing active ingredients. Studies were conducted to compare spray droplet spectra parameters from simulated and mimic sprays to those from an active ingredient spray. These sprays were atomized using two nozzles placed in airspeeds from 45 – 63 m/s in 2 m/s increments. In general, the volume median diameter (VMD) decreased by 30-50% as the airspeed increased. There were significant differences in droplet size between mimic sprays and those with active ingredient sprays. Results from AGDISP modeling showed increased downwind deposition with increased airspeed as a result of the increased number of finer droplets in the spray. The AGDISP results also showed differing amounts of downwind deposition at similar airspeeds from the different formulations. Downwind deposition modeling based on a simulated multi-pass spray application with reduced airspeeds near the downwind spray area border showed that the addition of the slower-speed passes near the edge can reduce total off-target movement. The results from these studies show that while mimic and simulated sprays can give similar atomization results and follow similar trends in effects of droplet size from changes in airspeed, active ingredients can have a significant effect on the atomization of spray solutions.