Detection and mapping of Amaranthus spinosus L. in bermudagrass pastures using drone imagery and deep learning for a site-specific weed management

Weed encroachment negatively affects pasture productivity by reducing herbage allowance, stocking rates, and livestock performance. Amaranthus spinosus L. is a weed species widely found in pastures worldwide and is considered challenging for ranchers due to its great potential for invasion, making it difficult to control. The high costs of chemical application and the global concern about environmental impacts restrict indiscriminate herbicide spraying in pastures. Site-specific weed management (SSWM) is a weed management strategy based on weed spot-spraying that has the potential to overcome these issues. Images from unmanned aerial vehicles (UAVs) can provide valuable information for weed mapping to drive the herbicide application in pastures. Deep learning techniques have been highlighted in image classification tasks. We developed a deep convolutional neural network (CNN)-based image segmentation model based on the U-Net architecture to detect and map Amaranthus spinosus in bermudagrass pastures using red-green-blue images acquired through UAV flying in moderate-high altitude. The images were acquired from twelve paddocks under three treatments (weed-free, weed-strips, or weed-infested) during the summer (2021-2022). The CNN model was able to detect around 80% of the A. spinosus with an average prediction accuracy of 94%. Our weed mapping showed the potential of using the U-Net model to generate a herbicide application map to be inserted into the sprayer system, reducing up to 76% of the amount of herbicide applied. Further studies are encouraged to increase the robustness of the model across species and development stages and develop sprayer systems to implement the spot-spraying in field conditions.