Abstract: The inventors provide the use of a chelating agent and an antimicrobial agent that is effective against a plant pathogenic microorganism to inhibit the growth of and/or kill a plant pathogenic microorganism on a plant; the use of a chelating agent to increase the activity of an antimicrobial that is effective against a plant pathogenic microorganism; a method of inhibiting the growth of and/or killing a plant pathogenic microorganism comprising administering to a plant in need thereof a chelating agent and an antimicrobial agent that is effective against a plant pathogenic microorganism; and a method of increasing the activity of an antimicrobial that is effective against a plant pathogenic microorganism comprising using said antimicrobial with a chelating agent.