The invention is a method and composition for treating biofilm using a high valency silver ion. In preferred embodiments of the invention, the anti-biofilm agent is used to preserve, disinfect or treat plant material, including seeds, leaves, stems, vessels, flowers, roots and fruits, and any surface, particularly disinfecting work or processing surfaces and seed or plant surfaces; in anti-microbial coatings; and in treating human, plant, and animal diseases and conditions