DETECTION AND QUANTIFICATION OF NURSERY SPRAY PENETRATION AND OFF-TARGET LOSS WITH ELECTRON BEAM AND CONDUCTIVITY ANALYSIS

Spray penetration and off-target loss from a conventional, air-assist, axial-fan sprayer and a high-clearance, boom-type sprayer were investigated in Honey Locust (Gleditsia triacanthos) and Canadian Hemlock (Tsuga canadensis) trees located in two different production nurseries. Aqueous tracer solutions of either Ca(NO3)2 foliar fertilizer or Cu(OH)2 fungicide were used in the experiments. Spray deposition distributions within canopies and off-target loss to drift and the ground were assessed via residues collected on foliage, electron microscope stubs, artificial plates, vertical and ground-level profile plastic tapes, and high-volume air samplers. Electron beam analysis (EBA) was used to assay residues on stubs, leaves, and needles placed and collected at several locations and heights in the canopy. Plastic tape samples were evaluated with a laboratory spray deposit analyzer using a conductivity detector. Both assessment methods used in the present study were useful for detection and quantification of Ca or Cu spray penetration within nursery canopies. The average spray deposit on upper surfaces of leaves was three times that deposited on lower surfaces within the Honey Locust trees. Spray deposit at the top of Canadian Hemlock tree canopies was 14 times higher than that at the middle and bottom of canopies. Spray deposit on ground targets greatly decreased as the distance from the spray path increased in both nurseries; however, airborne spray deposits did not decrease as much with increasing downwind distance as ground deposits.