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

Abstract

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. Traditional spray deposition assessments lack spatial dimensionality. Nighttime UV-fluorescence photography of proxy dye accurately assesses spray deposition patterns. Spatial heterogeneity and drift increase with agricultural spray drones compared to ride-on sprayers. Weed infestation annotated via grid-overlaid aerial images resolves drift more than spatial heterogeneity. Despite erratic deposition, spray drones conserve or enhance weed control compared to a handheld boom sprayer. Spraying herbicides evenly is crucial for effective weed control. While the use of agricultural spray drones is increasing, there is limited understanding of their spray uniformity and drift potential. Inconsistent spray patterns can lead to overapplication or under-application, reducing weed control efficacy, or causing unintended crop damage. This study examined how agricultural spray drones, ride-on sprayers, and handheld spray guns distribute herbicides, using UV-fluorescent dye and nighttime imagery or aerial photos to detect weed population shifts. Results showed that ride-on sprayers applied chemicals more evenly, while drones and spray guns had more overapplication, especially with drones spraying too much directly below. Drones also caused more drift, but they achieved better weed control potentially due to fine spray particles covering more weeds. Although drones are less uniform, they can be effective for weed control but pose a higher risk of environmental impact through drift.