Plant diseases are the most pressing threat to global efforts to sustain and improve agricultural outputs. Nanotechnology offers potential solutions for enhancing agricultural output amidst rising global populations and escalating challenges from pests and diseases. While conventional pesticides are effective, they pose significant environmental and human health risks. Researchers are thus seeking sustainable alternatives through nanotechnology. Green nanoparticles (NPs) produced using plant extracts show promise in enhancing pesticide delivery, effectiveness, and environmental safety for crop protection. Plant-based NPs can be synthesized through intracellular and extracellular methods, where plant metabolites reduce and stabilize the nanoparticles. These NPs possess intricate structures and diverse physicochemical properties, essential for managing phytopathogens. This plant-mediated manufacturing approach yields substantial quantities of high-quality NPs with precise dimensions, ensuring biocompatibility and non-toxicity. NPs exhibit antimicrobial properties through multiple mechanisms, including surface charge attraction, reactive oxygen species (ROS) production, and membrane damage, which combat phytopathogens and improve crop health. Despite their potential, the deployment of NPs raises a few concerns about environmental dispersal, bioaccumulation, and potential ecological impacts, necessitating comprehensive toxicological studies and standardized protocols for safe utilization. Thus, successful use of plant-mediated green synthesis of NPs and mitigating associated hazards require multidisciplinary collaboration and leveraging technological advancements. This chapter presents an in-depth study of nanoparticle production using plant-based techniques and their application as antimicrobial agents against plant diseases.