Neem leaf extract was exploited to biosynthesize zinc oxide nanoparticles (ZnO-Neem NPs), in which endogenous phytochemicals simultaneously reduced Zn²⁺ and capped the forming crystallites. UV-Vis spectroscopy revealed a sharp excitonic peak at 363 nm corresponding to a 3.42 eV band gap, and FTIR confirmed phytochemical-derived surface functionalities. TEM showed coexisting hexagonal nanorods and quasi-spherical particles, while DLS yielded a monodisperse hydrodynamic diameter of 47.2 nm (PDI=0.052). In vitro, the nanoparticles inhibited the rice blight pathogen Xanthomonas oryzae pv. oryzae with an IC₅₀ of 36.8 µg.mL^-¹. Greenhouse assays on KDML105 rice seedlings demonstrated a hormetic response: foliar application of 50 µg.mL^-¹ ZnO-Neem NPs enhanced shoot and root length by 24% and 48%, respectively, whereas doses >100 µg.mL^-¹ were neutral or inhibitory. These results underline the dual functionality of neem-driven ZnO NPs as an eco-friendly bactericide and micronutrient nanofertilizer, offering a scalable and sustainable strategy for integrated management of bacterial blight and growth promotion in rice.