Effect of fan speed and electrostatic charge on deposition of orchard canopy sprays

This work is a continuation of an ongoing project, performed in an orchard, to determine the effect of airflow velocity on electrostatic forces in plant canopy. Field applications were made using the fluorescent tracer manganese(II) sulfate (MnSO4), applied through seven electrostatic pressure-swirl nozzles with and without charge when fitted to an axial-fan orchard airblast sprayer with selected fan speeds of 1000, 1500, and 2000 rpm. Spray deposition was analyzed for two varieties of semidwarf apple trees referred to as M9 and M26 East Malling Roots. The field experiment was performed with single and twin passes of the sprayer at a constant ground velocity of 0.82 km/h. Statistical methods were used to analyze and to compare the affect of the selected fan speeds on electrostatic forces at sampling locations between the uncharged and charged sprays. The charged spray showed an increase of 2.47-2.51-fold at a fan speed of 2000 rpm for one pass and two passes, respectively, for M9 trees. The charged spray deposition was superior to the uncharged spray by 1.65-1.89-fold at 2000 rpm for both passes. There was no significant difference between the charged and uncharged spray deposition for the fan speed of 1500 rpm for two passes. It therefore emerged that the charged spray was superior to the uncharged spray at a fan speed of 2000 rpm.