EFFECTS OF VOLUME RATE AND SPRAY PRESSURE OF AN AIR-ASSISTED SPRAYER ON PESTICIDE DISTRIBUTION AND DRIFT ON PEAR PREES

Pear orchards in Argentina are predominantly sprayed with an axial fan airblast sprayer. In this system, the forced air jet transports the spray droplets to the plant surface. The droplets are produced by an hydraulic nozzle, hollow cone type. The nozzles quality and operating pressure affect the spray droplet spectra of pesticide distribution and drift. The large radial spray plume possesses has a significant risk of off target contamination by spray drift and losses to the ground. The objective of this research was to evaluate the spray deposit and off target contamination on pear orchards, in relation to nozzle quality and spray pressure. The treatments were: 1) 2145 L ha^-1 , 2000 kPa spray pressure with (a) common quality hollow cone nozzle (ceramic tip and metal whirl core, deformed whirl chamber) and (b) high quality hollow cone nozzles in ceramic (non-deformed whirl chamber), and, 2) 1560 L ha^-1 1000 kPa spray pressure with high quality hollow cone ceramic nozzles. Fluorescein-sodium tracer was used at 80 g ha^-1 and detected by a fluorimeter. Pools of thirty leaves were taken at three levels of tree height (top, middle and bottom) and two levels in depth (out and into the canopy). The losses in soil were collected on plastic collectors within and between tree rows. Measurements were carried out in 4 consecutive rows. The airborne drift was collected on pipe cleaners at two heights (2 and 6 m). The reduce volume rate had lesser deposits in the upper part of the tree in comparison with the other treatments. In all treatments the soil deposits (endodrift) and airborne (exodrift) were higher in the zones near the sprayer. Although treatments were not different among them, the deposits found in the outside part of the canopy were greater than those in the inner locations.