Comparing trunk applications and off-target movement from a backpack sprayer and an air-assisted sprayer with and without laser-guided variable-rate technology

Authors: MATHEWS, L - University Of Tennessee; MCKIM, K - University Of Tennessee; WRIGHT, W - University Of Tennessee; Zhu, Heping; SUN, XIAOCUN - University Of Tennessee; FULCHER, A - University Of Tennessee

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2026
Publication Date: 6/8/2026
Citation: Mathews, L.F., Mckim, K., Wright, W.C., Zhu, H., Sun, X., Fulcher, A. 2026. Comparing trunk applications and off-target movement from a backpack sprayer and an air-assisted sprayer with and without laser-guided variable-rate technology. HortScience. 61(5):862–873. https://doi.org/10.21273/HORTSCI19139-25.
DOI: https://doi.org/10.21273/HORTSCI19139-25

Interpretive Summary: Flatheaded borers are one of the most problematic pests to damage orchard and nursery trees. Because they inhabit and attack only tree trunks, it has caused tremendous pesticide waste by using conventional sprayers that apply chemicals constantly across entire trees multiple times during a growing season. In this research, an intelligent spray technology developed by USDA-ARS engineers at Wooster, Ohio was retrofitted on a conventional orchard sprayer for targeted precision applications. It was tested to automatically spray only trunks of maple trees in an ornamental nursery field in Tennessee. Spray deposition quantities on trunks and off-target losses were compared with those from a hand-held backpack sprayer and the same orchard sprayer in conventional mode. Test results demonstrated that the sprayer with the intelligent spray control was able to provide equivalent spray deposition on trunks compared to the same sprayer without the intelligent control while the intelligent spray reduced total spray volume by 70%, ground loss by up to 20% and airborne drift by up to 62%. In contrast, the hand-held sprayer used the least spray volume and produced the lowest off-target losses without compromising spray deposition quantity to trunks but it was the most time intensive. Thus, large reductions in pesticide use and labor intensity could be achieved by automatically spraying only trunks for treatment of flathead bores with the intelligent spray technology, thereby reducing annual chemical inputs and labor costs for orchard and nursery growers.

Technical Abstract: Red maple (Acer rubrum) trees produced in single-row and triple-row blocks, were sprayed with a CO2 backpack sprayer outfitted with a custom-made, dual-nozzle wand and an air-assisted, “air-blast” sprayer equipped with intelligent, laser-guided variable-rate spray technology operating in constant-rate, conventional mode, and intelligent, variable-rate mode to compare application efficiency, spray coverage and deposits on tree trunks, and in non-target locations within and outside the blocks. Artificial targets, i.e., stainless steel mesh and water sensitive paper (WSP) cards and trunk wraps were used to characterize spray performance. Fluorescent tracer was added to tanks to quantify spray deposits. Coverage and deposits on both non-target samples within the block and drift samples were generally lowest in the backpack treatment regardless of row or block compared to the constant-rate and variable-rate air-blast treatments, however, all treatments had a large quantity of overspray at the base of the trunk. For air-blast sprayer treatments in the triple-row block, targets (or target faces) that were directly adjacent to the sprayer, tended to have the highest coverage and deposits. However, for both air-blast treatments lower wraps in the middle row, Row 2, which was equidistant from the sprayer on either side of the block, had more coverage than Row 1. Additionally, for the constant-rate treatment both upper and lower wraps in Row 23 2 had uniform coverage, i.e., no direction effect. The backpack treatment applied the smallest total volume while achieving uniformly high coverage and deposits and came the closest to reaching 100% trunk coverage across all row types and wrap heights with the smallest amount of airborne drift. Between the air-blast treatments, the constant-rate output nearly 70% more total spray volume than the variable-rate but both achieved similar trunk coverage in both blocks. More research is needed to investigate the feasibility of using intelligent, laser-guided variable-rate spray technology for the application of contact insecticides to tree trunks.