Characterizing spray deposits for control of trunk pests from an experimental air-blast sprayer with 5-port nozzle bodies

Trunk boring insect pests can cause severe plant damage and death thus causing nursery operators to incur significant economic losses. In order to control trunk borers with contact insecticides, thorough coverage is presumed necessary. While not designed for trunk applications, nursery operators commonly use air-blast sprayers for this purpose due to their high labor efficiency and perceived ability to adequately spray trunk and canopy pests simultaneously. This study quantified spray deposits on red maple trunks in a 3-row block at two application rates, 1380 and 1070 L ha(-1), from a vineyard air-blast sprayer equipped with laboratory-designed 5-port nozzle bodies known to improve coverage uniformity. Water sensitive wraps placed at four heights (11.4 to 77.5 cm) on trunks in each row were analyzed for coverage after spraying the block from both sides with all 20 nozzles on the proximal side of the sprayer. While there was a row x direction x height interaction (p=0.0304), within each row, portions of wraps facing the same direction did not differ in coverage regardless of height. On the interior row only, coverage was greater at 1070 than at 1380 L ha(-1) (p<0.0001), possibly due to zero wind allowing greater penetration into the interior row. For both rates, while the face of the trunk proximal to the sprayer in the exterior rows had high coverage, ranging from 77 to 95%, the opposite side averaged just 38% coverage, resulting in a total coverage of only 53% on average. High coverage is possible for a wide range of trunk heights on the proximal face of exterior rows; however, for a 3-row block of trees, applications of 1380 L ha(-1) or less from this specialized sprayer may not achieve 100% coverage around the entire trunk. Further optimization to sprayer type, technology, and adjustments, such as application rate, should be explored.