The build-up of synthetic dyes in the environment and aquatic ecology is a significant environmental issue due to their inability to break down naturally. The overuse of chemical fungicides also poses a threat to the environment due to their accumulation and fostering of fungal resistance. Hence, the study was conducted to detect the antifungal properties and photocatalytic activity of greenly synthesized iron oxide nanoparticles (IONPs) prepared using the Hibiscus sabdariffa flower extract. The biogenic IONPs showed the highest photocatalytic activity against rhodamine B dye at a concentration of 4.0 mg/ml. The biogenic IONPs also demonstrated effective antifungal properties against Penicillium digitatum and Aspergillus niger strains, with relative inhibition percentages of mycelial growth being higher than those with the metalaxyl + mancozeb fungicide at 800 ppm concentration. The efficient photocatalytic activity of the biogenic IONPs against rhodamine B dye and their effective antifungal properties suggest their potential use as safe substitutes for commercial fungicides.