Spray characteristics of rotary micro sprinkler nozzles used in orchard pesticide delivery

Authors: GULER, HUSEYIN - Ege University; ZHANG, ZHIHONG - Kunming University Of Science And Technology; Zhu, Heping; GRIESHOP, MATTHEW - Michigan State University; LEDEBUHR, MARK - Application Insight, Llc

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2020
Publication Date: 12/1/2020
Citation: Guler, H., Zhang, Z., Zhu, H., Grieshop, M., Ledebuhr, M. 2020. Spray characteristics of rotary micro sprinkler nozzles used in orchard pesticide delivery. Transactions of the ASABE. 63(6):1845-1853. https://doi.org/10.13031/trans.13445.
DOI: https://doi.org/10.13031/trans.13445

Interpretive Summary: Rotary micro sprinkler nozzles have been recently considered for use in solid set canopy delivery systems to deliver pesticides in orchards and other trellised perennial cropping systems. Compared to radial air-blast orchard sprayers, the solid set canopy delivery systems have advantages in producing less off-target spray drift, reducing soil compaction, reducing worker exposure, and increasing pesticide application flexibility. However, achieving consistent spray coverage has been challenged with these systems which are developed for irrigation purposes but not for the delivery of plant protectants. Characterization of the micro sprinkler nozzles would provide scientific guidelines to assist in choosing proper sprinkler nozzles to improve coverage and potentially guide the development of new solid set canopy delivery systems. In this research, droplet size distributions from different rotary micro sprinkler nozzles were determined with a droplet laser image analysis system. Spiral-shaped spray patterns were found beyond the spinning discharge port with varied droplet density distribution on the patterns. Droplet sizes were greatly influenced by the nozzle orifice diameter, operating pressure, flow rate and sampling location. A multiple variable regression model was developed to predict droplet sizes, which can be a helpful tool when instrumentational measurements are not available. This research also revealed that the size range of droplets produced from the rotary micro sprinkler nozzles could minimize spray drift while maintaining efficacy in orchard and vineyard pesticide applications.

Technical Abstract: Micro sprinkler nozzles can be used for both irrigation and pesticide applications in orchard systems, but little to no information is available on their droplet size distributions. In this study, the droplet size distributions were investigated and described for rotary micro sprinkler nozzles with five different orifice diameters. A particle/droplet laser image analysis system was used to measure droplet spectrum at two pressures (207 and 310 kPa) and two radial distances (0.25 and 0.85 m) from the sprinkler nozzle center. Nozzle orifice sizes, rotation speeds and flow rates were also measured. Droplet sizes varied with the nozzle tip orifice size, operating pressure and sampling location. Spiral-shaped spray patterns formed due to the spinning discharge port, within which droplet densities varied with location, nozzle diameter and operating pressure. The volume medium diameter (DV0.5) for green-black, orange-blue, black-black, blue-black and red-gray nozzles were 317, 338, 379, 352 and 218 µm at 207 kPa, and 283, 250, 283, 270 and 222 µm at 310 kPa, respectively. A multiple variable regression model was developed to predict DV0.5 discharged from the sprinkler spinning nozzles. Test results demonstrated that the rotary micro sprinkler nozzles produced medium to coarse droplets that could be used to minimize spray drift while maintaining efficacy in orchard pesticide applications.