A method to spatially assess multipass spray deposition patterns via UV fluorescence and weed population shifts

Spray deposition patterns from agricultural sprayers are traditionally sampled discretely along a field transect accounting for 0.5% or less of the treated area. Such methods may not fully capture the dimensional variability inherent in large-scale, multiple-pass spray applications, especially evident from an agricultural spray drone (ASD). This study investigated the utilization of UV-fluorescent dye and nighttime aerial imaging techniques to assess large-scale, multipass spray deposition patterns. Accuracy of digital hue from UV-fluorescent photography to predict deposition of proxy dye was confirmed via fluorometry assessed intensity levels of extracted UV-fluorescent dye from 384 Petri dishes placed prior to treatment. Results showed that ASD applications, regardless of nozzle type, exhibited greater spatial variability within the target area compared to ride-on sprayer applications, primarily due to overapplication. Additionally, the ASD generated spray drift to adjacent nontarget areas that was at least three times more than that of ride-on and spray-gun sprayers. Multipass deposition was further assessed via in situ smooth crabgrass infestation following treatment with quinclorac or topramezone by multipass ASD or hand-held, four-nozzle spray boom. Weed infestation annotated from overlaid grids with 9.3-dm² ground resolution inconsistently detected spatial heterogeneity between transects assessed along the center and edge of each sprayer pass. The ASD controlled smooth crabgrass 11% more than the hand-held sprayer, albeit with an 18% increase in spray drift to nontarget areas, similar to the UV-fluorescence study. Digitally assessed average hue of fluorescence photography appears to be a viable method to assess multidimensional and continuous spatial relationships of spray deposition.