The use of chemical pesticides has led to adverse effects on human health and the environment, prompting the exploration of alternative solutions. This study successfully biosynthesized iron oxide nanoparticles (Fe₃O₄ NPs) using chicken egg albumin, which served as reducing and capping agents, and evaluated their antifungal efficacy against Macrophomina phaseolina. The fungicidal potential of Fe₃O₄ NPs was assessed in vitro, demonstrating enhanced inhibition of M. phaseolina’s radial growth with increasing concentrations from 100 ppm to 300 ppm. Dielectric properties were also studied, revealing advantageous current conduction processes and conductive network development with temperature variation, which is particularly beneficial in the low-frequency range. At a fixed pH, dielectric studies showed increased mobile carrier movement and polarization with rising temperature at a fixed frequency. The photocatalytic activity of Fe₃O₄ NPs was assessed for the degradation of methylene blue (MB), an organic dye, under solar irradiation. In this study, Fe₃O₄ NPs photocatalysts achieved 89% (MB) degradation within 75 min. This research underscores the potential of using chicken egg albumin for the biosynthesis of Fe₃O₄ NPs. It offers a promising alternative for plant disease control and highlights their suitability for integration into eco-friendly plant protection strategies.