Metallic nanoparticles have been reported to have wide spread applications in the field of agricultural with a potential to enhance the activity natural substances to replace hazardous chemical fungicides and pesticides. Higher size to volume ratio, greater surface area, optimum efficacy, and immense precision are some of the benefits of employing nanotechnology in agricultural formulations. In this study, copper nano-biocomposites have been successfully synthesized using chitosan, a naturally occurring polymer and an organically available ascorbic acid. We report the appearance of the characteristic brick-brown color in aqueous solution that indicates the formation of copper nanoparticles. These particles were subjected to various physico-chemical characterizations using UV-Vis spectrophotometer, DLS, Zeta Potential, TEM, TGA, and FTIR to understand the morphology, chemical, and physical profiling. It was inferred that ascorbic acid acted as reducing agent while chitosan as capping agent to stabilize the colloidal copper nanoparticles of 20–120 nm size. In aqueous solution, the particles were observed to be monodispersed with minimum aggregation. The synthesized nanoparticles showed significant antifungal and antibacterial activity against common notorious agricultural plant pathogens, viz., Fusarium sp., Aspergillus sp., Alternaria alternata, Pythium sp., and Bacillus cereus, assayed using poisoned food method. The antimicrobial activity was showcased at a minimum concentration of 0.1–0.7% for different organisms. Furthermore, filed trial studies were performed on ginger (Zingiber officinale) plantations for a period of 8 weeks which substantiated with our lab results. These studies validated our claim of antifungal activity and simultaneously furnished us with toxicity results. The use of eco-friendly, nontoxic, biodegradable, and environmentally safe raw materials and the resultant nanoparticle solution ensure that the finished product does not induce any threat to the environment or human and shows maximum efficacy at minimum concentration. [ABSTRACT FROM AUTHOR]