ASHS 2025 Conference

Air-blast sprayers with intelligent spray technology can apply pesticides more efficiently to tree canopies than conventional sprayers. However, little research has examined their effectiveness for trunk applications to control pests such as flatheaded borer (FHB). FHB larvae chew directly into the trunk upon hatching, necessitating thorough coverage with contact insecticides. Our objective was to explore the potential of using intelligent variable-rate spray technology to achieve thorough coverage on tree trunks. A red maple (Acer rubrum) block was divided into three plot-row-types: single-row (SR), double-row (DR; South and North rows), and triple-row (TR; South, interior, and North rows). Water sensitive paper (WSP) wraps were used to assess spray coverage. Wraps were secured around trunks of ten trees per row at 15 and 40 cm above the ground. Plots were sprayed with water using a Jacto A400/850 air-blast sprayer in constant-rate (CR) and variable-rate (VR) modes using the Smart Apply intelligent spray control system. CR discharged 69% higher spray volume than the VR mode (P < 0.0001). SR had >99% coverage; coverage in SR was not affected by spray mode or wrap height (P ≥ 0.0592). For DR, coverage ranged from 98.4% to 99.9%, and spray mode did not affect coverage on upper wraps (P ≥ 0.0829) within a row, while CR (99.6%) had lower coverage than VR (99.9%; P = 0.0043) for lower wraps in the northern row. However, TR coverage varied with the spray mode and wrap height (P < 0.0001). Upper wraps in the southern and interior rows had higher coverage from CR than VR, 98.6% versus 89.9% (P = 0.0019) and 98.7% versus 78.8% (P = 0.0137), respectively. For lower wraps, both the southern and interior rows had higher coverage from CR than VR, 98.5% versus 93.4% (P = 0.0019) and 99.5% versus 94.0% (P = 0.0137), respectively. Coverage was very high, i.e., ≥98.0% for 18 of 24 treatment combinations and ≥89.9% for 23 of 24 treatment combinations, but did not achieve 100%. There was no advantage to CR for SR or DR. For all plot-row-types and spray modes, the spray rate was higher than desired. CR sprayed 480, 251, and 210 GPA in the SR, DR, and TR plots, respectively, while VR discharged 239, 156, and 140 GPA. Future research should examine the use of adjuvants to increase coverage and determine a coverage range that balances acceptable FHB control, labor costs, and spray volume.