Antimicrobial compositions of phosphorous acid-solubilized copper ammonium complex and phosphorous acid-solubilized copper-zinc ammonium complex combined with a water soluble salt of sorbic acid, such as potassium sorbate, are disclosed. The antimicrobial activity of the compositions are synergistically enhanced with the addition of a water soluble salt of sorbic acid to create a composition that is highly effective against pathogens such as plant pathogenic microorganisms including oomycetes, fungi, and bacteria.
