Evaluation of Deposition and Coverage by an Air-Assisted Sprayer and Two Air-Blast Sprayers in a Citrus Orchard

Abstract

Abstract. This study evaluated a retrofit air-assisted sprayer, a conventional axial-fan air-blast sprayer, and a multifan vertical air-blast sprayer for their application efficiency in citrus orchards. Field experiments involved three spray application treatments (three sprayers) replicated three times. Each replication included two short, two medium, and two tall tree canopies. Green cards and water-sensitive papers were used as passive samplers to evaluate spray deposition and coverage, respectively. The samplers were located laterally on the canopy surface and 0.6 m inside the canopy, and vertically at canopy heights of 0.5, 1.0, 1.5, and 2.0 m for short canopies and 1.0, 2.0, 3.0, and 4.0 m for medium and tall canopies. Pyranine 10G tracer dye dissolved in water was used as the spray mix. Treatments were applied at 2805 L ha -1 (300 gal acre -1 ) for all sprayers, except the retrofit sprayer, for which the application rate varied based on the canopy size. Results revealed that deposition and coverage on the canopy surface was higher than at 0.6 m inside the canopy for all sprayer treatments and canopy sizes. The retrofit sprayer resulted in comparable spray deposition with 30% and 70% less spray volume for medium and short canopies, respectively, compared to the other two sprayers. The multifan vertical sprayer resulted in significantly less deposition and coverage (at the 5% level) for the lower sections of short canopies and for 0.6 m inside tall canopies. Thus, a multifan vertical sprayer may be more suited for applications in commercial orchards with medium, less dense, and hedged canopies, whereas a retrofit air-assisted sprayer may be best for all types of citrus canopies, as it adjusts the air-assist and liquid flow rates based on canopy size.