Plant-derived volatile organic compounds (VOCs) have garnered increasing attention for postharvest disease management due to their antifungal properties and eco-friendliness. This study investigated the antifungal activity and mechanisms of 1-octanol, a plant-derived VOC, against Botrytis cinerea and evaluated suitable gels for its sustained release. The results demonstrated 1-octanol significantly inhibited B. cinerea conidial germination and mycelial growth, effectively controlling gray mold in grapes and sweet cherries. Biochemical assays and ultrastructural observations revealed 1-octanol disrupts cell membrane integrity, induces reactive oxygen species (ROS) accumulation, and causes cell death. Transcriptome analysis revealed 1-octanol treatment downregulated ribosome biogenesis genes, upregulated glutathione metabolism genes, and notably suppressed key pathogenicity-related genes. Moreover, curdlan was identified as the optimal gel for 1-octanol release, with the 1-octanol-loaded curdlan hydrogel effectively preventing gray mold in grapes. These findings suggest 1-octanol is a promising antifungal fumigant, and its curdlan-based hydrogel formulation could serve as a sustainable strategy for postharvest gray mold management.