Agricultural Jiaosu is a fermented product made from plant waste that effectively controls gray mold disease in tomatoes through two mechanisms: it directly kills the fungus with organic acids, and it strengthens the plant’s natural defenses. When applied as a spray to tomato leaves once a week, it reduced disease by 55%, made plants grow taller and stronger, and boosted the plants’ protective enzymes. This natural alternative to chemical fungicides offers a sustainable and safe way to protect tomato crops while maintaining environmental health.