Research Note: Effects of Ozonated Water Spray Droplet Size and Distance on the Dissolved Ozone Concentration at the Spray Target

Dissolved ozone concentration (DOC) of ozonated water (OW) sprayed from four different distances using three different droplet sizes (expressed in terms of Sauter mean diameter; small, medium, large) was measured at the spray target to obtain fundamental data for improving disease control efficacy when spraying OW onto plants. DOC in the OW at the spray target decreased with decreasing droplet size. DOC was also greatly reduced at the typical spray distances of 0.50 to 0.75 m to less than one-seventh of the initial DOC (2.2 mg/L^?1) in the sprayer reservoir, and DOC one-third lower than the initial DOC was observed even at the shortest spray distance of 0.05 m for all three nozzle sizes used. Based on the results of these experiments, disease control efficacy by spraying OW can be improved by minimizing the spray distance and using a nozzle that produces a larger spray droplet size, within the range such that adhesion efficiency of OW to the leaf surface is not greatly reduced.