Inconsistencies in efficacy of ultra-low volume (ULV) ground applications in the literature are linked to the lack of adjustments in sprayer parameters. To investigate the effect of nozzle orientation of a truck-mounted ULV sprayer on application efficacy, a study was conducted at St. Johns County Fairground, Elkton, FL, during the summer of 2014. The efficacy was assessed by mortality of caged adult Aedes aegypti, spray deposition, and droplet size spectrum up to 122 m from the spray line. Aqualuer 20-20 (20.6% permethrin active ingredient [AI] and 20% piperonyl butoxide [PBO]) was applied at the maximum label rate with the nozzle pointed 45° upward, horizontal (0°), or 30° downward. Mortality was recorded after 24 h, deposition was determined with fluorometry, and droplets were measured with DropVision. Overall, horizontal nozzle angle spraying Aqualuer 20-20 achieved the highest efficacy followed by a 30° downward angle, while a 45° angle showed the least efficacy in open field tests. The mortality data showed complete mortality from a 0° nozzle up to 122 m from the spray line except for 1 location at 122 m in 1 replication. The mortality from a 30° downward orientation was lower beyond 30 m from the spray line, while the mortality from a 45° upward orientation was low close to the spray line and beyond 30 m. Horizontal orientation had higher deposition than other orientations, but the differences were not significant. There was also no significant difference in droplet spectrum from all orientations.
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