Simulation-based nozzle density optimization for maximized efficacy of a machine vision-based weed control system for applications in turfgrass settings

Targeted spraying application technologies have the capacity to drastically reduce herbicide inputs, but to be successful, the performance of both machine vision-based weed detection and actuator efficiency needs to be optimized. This study assessed (1) the performance of spotted spurge recognition in 'Latitude 36' bermudagrass turf canopy using the You Only Look Once (YOLOv3) real-time multiobject detection algorithm and (2) the impact of various nozzle densities on model efficiency and projected herbicide reduction under simulated conditions. The YOLOv3 model was trained and validated with a data set of 1,191 images. The simulation design consisted of four grid matrix regimes (3 x 3, 6 x 6, 12 x 12, and 24 x 24), which would then correspond to 3, 6, 12, and 24 nonoverlapping nozzles, respectively, covering a 50-cm-wide band. Simulated efficiency testing was conducted using 50 images containing predictions (labels) generated with the trained YOLO model and by applying each of the grid matrixes to individual images. The model resulted in prediction accuracy of an F1 score of 0.62, precision of 0.65, and a recall value of 0.60. Increased nozzle density (from 3 to 12) improved actuator precision and predicted herbicide-use efficiency with a reduction in the false hits ratio from similar to 30% to 5%. The area required to ensure herbicide deposition to all spotted spurge detected within images was reduced to 18%, resulting in similar to 80% herbicide savings compared to broadcast application. Slightly greater precision was predicted with 24 nozzles but was not statistically different from the 12-nozzle scenario. Using this turf/weed model as a basis, optimal actuator efficacy and herbicide savings would occur by increasing nozzle density from 1 to 12 nozzles within the context of a single band.