SPRAY DEPOSITION INSIDE TREE CANOPIES FROM A NEWLY DEVELOPED VARIABLE-RATE AIR-ASSISTED SPRAYER

Conventional spray applications in orchards and ornamental nurseries are not target-oriented, resulting in significant waste of pesticides and contamination of the environment. To address this problem, a variable-rate air-assisted sprayer implementing laser scanning technology was developed to apply appropriate amounts of pesticides based on tree canopy characteristics including tree height, width, volume, foliage density, and occurrence. The new sprayer performance was evaluated in an apple orchard by quantifying spray deposition inside canopies at three different growth stages (leafing, half-foliage, and full-foliage) with three sprayer treatments: the new variable-rate sprayer (S-1), the same sprayer without the variable-rate function (52), and a conventional air-blast sprayer (S-3). Their spray coverage and deposits inside canopies were measured and compared with water-sensitive papers and nylon screens. The three sprayer treatments provided fairly consistent spray coverage and deposits in the spray direction (or canopy depth direction) at the leafing stage. The variations in spray coverage and deposits in the spray direction increased considerably for S-2 and S3 at the half-foliage and full-foliage stages. S1 produced better uniformity in spray coverage and deposits across the tree height direction than S2 and S3 at all growth stages. Compared to constant-rate sprayers, the new variable-rate sprayer only consumed 27% to 53% of the spray mixture while still achieving adequate spray coverage inside the canopies. In addition, the spray deposition from the new sprayer was very consistent regardless of the canopy growth stage. Therefore, the new sprayer increased spray efficiency and improved spray accuracy by greatly lowering the possibility of overspray, resulting in reduced spray costs and potential reduction of environmental pollution.