Developmentof Multi-Unit Orchard Centrifugal Spray System and Deposition Evaluation on Pear Trees

An air-assisted sprayer is a primary tool for pest and disease control in orchards. However, conventional systems often suffer from insufficient deposition at the canopy top and poor coverage on the abaxial leaf surfaces, which are highly susceptible to pests and diseases. To address this limitation, a centrifugal air-assisted spraying system was developed to generate finer droplets and improve deposition distribution within tree canopies, particularly on the abaxial surfaces. Vertical deposition tests were conducted to characterize the droplet distribution pattern of the system. Single-unit spray tests were then performed under Foliage Area Volume Density (FAVD, the foliage area per unit canopy volume) of 3.3 and 1.4 m2·m−3, and three outlet air velocities (4, 8, and 11 m·s−1) to evaluate the effects of these variables on coverage and droplet density. Comparative experiments between the centrifugal and a conventional hydraulic system were also carried out at the same flow rate (3.6 L·min−1), as well as at a 30% reduced application rate for the centrifugal system. The results showed that the droplet distribution pattern followed a normal distribution and correlated well with the spindle-shaped pear tree canopy. At both FAVD levels, an air velocity of 8 m·s−1 produced superior leaf coverage compared with 4 and 11 m·s−1. At the same flow rate, the centrifugal system achieved significantly higher coverage on the abaxial surfaces of outer canopy leaves than the hydraulic system. Remarkably, even with a 30% reduction in application volume, the centrifugal system maintained coverage and droplet density comparable to those of the hydraulic system at its full rate. We conclude that the centrifugal air-assisted orchard spraying system effectively improves pesticide deposition distribution within pear tree canopies, with particular advantages in depositing droplets on the abaxial leaf surfaces. Future work will include a systematic assessment of spray drift potential to further evaluate its field applicability and environmental compatibility.