Juglone (Regianin, 5-Hydroxy-1,4-naphthoquinone), a natural naphthoquinone found in the black walnut and other plants, has moderate antifungal activity and growth-stimulating effects to many types of plants. It sometimes can be used as an herbicide, as a dye for cloth and inks, and as a coloring agent for foods and cosmetics.Solutions are unstable and should be fresh-prepared.