Variation of spray deposit and loss with air-jet directions applied in orchards

Axial fans with a radial air flow have been most commonly used in fruit growing areas. These generate a large radial plume which is poorly targeted for modern intensive orchards. A high-volume directed air-jet system (HVDAS) sprayer, based on a standard axial fan has been developed to determine the influence of the air jet direction generated by the sprayer on the in-canopy spray deposit and off-target loss in orchards of different tree row volumes. Three sprayers with axial fans but with different air discharge systems were compared (conventional, cross-flow, HVDAS with the air spouts directed at 20 and at 40 degrees upwards). The treatments were carried out in dwarf and semi-dwarf orchards. In modern orchards, the HVDAS sprayer with air spouts set 20 degrees upwards produced a higher in-canopy deposit and a lower off-target loss than the conventional and cross-flow sprayers. Further raising of the air spouts directing the air-jets at 40 degrees upwards, increased the spray loss and enhanced the risk of airborne drift without any influence on spray deposit. (C) 2000 Silsoe Research Institute.