Variable rate spraying in varied micro-meteorological conditions
Keywords:Airblast sprayer, Adjustable air-assistance, Crosswind, Spray coverage, Citrus.
This study evaluated effects of crosswind on the variable rate sprayer application treatments spray coverage and deposition on different citrus canopy sizes. The axial-fan airblast sprayer retrofitted with variable liquid- and air-assist rates was field-tested with different crosswind conditions on small (about 2 m tall and < 1.5 m wide) and medium-sized (about 3 m tall and < 2.5 m wide) canopies. Crosswinds of 1.3, 2.7, and 4.0 ms-1 on the canopies being sprayed were generated using the stationary conical air shaker as the air blower unit. Water sensitive papers (WSPs) were used to collect droplet deposits and image processing software was used to analyze the WSPs scanned at 600 dpi. Percent spray coverage on the WSPs was found to be one of the most suited parameters to evaluate the effectiveness of spray application treatments. Overall, the variable rate spray application treatments had comparable spray coverage on respective canopies (front, middle, and across WSP locations in the canopy) during all crosswind conditions. For both types of canopies, spray coverage was higher on the canopy front and decreased as the spray penetrated inside (i.e. canopy middle) and across. Due to coalescing, larger droplets (Dv,0.5 [volume median diameter] = 838 to 2,624 µm) were formed on the WSPs located on canopy front, whereas coalescing reduced as the spray penetrated inside (Dv,0.5 = 391 to 1,625 µm on canopy middle) and across the canopy (Dv,0.5 = 307 to 508 µm).
Keywords: airblast sprayer, adjustable air-assistance, crosswind, spray coverage, citrus