EFFECT OF PROTECTIVE SHIELDS ON DRIFT AND DEPOSITION CHARACTERISTICS OF FIELD SPRAYERS

Field trials were conducted to determine the effectiveness of shields in reducing off-target droplet drift from ground-rig sprayers. Sprayer booms ranging in width from 10 to 13.5 m and equipped with commercially available shields were operated along a 150-m swath in a field of approximately 20-cm-tall spring wheat in wind speeds ranging from 10 to 35 km h-1. Airborne drift was measured using aspirated air samplers. The use of an 80-degrees flat fan tip (8001) at a pressure of 275 kpa and a ground speed of 8 km h-1 resulted in 7.5% of the 50 L ha-1 spray solution drifting off the target area. The use of protective cones with 8001 tips without lowering the boom reduced airborne drift by 33% at a 20 km h-1 wind speed, while a 65-85% drift reduction was accomplished with the combination of solid or perforated shielding and lowering the sprayer boom. Increasing the application rate to 100 L ha-1 by using 8002 tips reduced drift of the unshielded sprayer by 65%. Decreasing application rate to 15 L ha-1 by using 800017 tips increased drift by 29% despite the use of a shield. Off-target drift increased with increasing wind speeds for all sprayers, but the increase was less for shielded sprayers and coarser sprays. The decreased droplet size of spray from 110-degrees tips increased drift when the boom height was the same as for 80-degrees tips. High wind speeds, lower carrier volumes and finer sprays, 110-degrees tips, and solid shields tended to decrease on-swath deposit uniformity, whereas a perforated shield or cones did not affect deposit uniformity.