Provided are a method for remarkably potentiating plant disease-controlling effect and a method for controlling plant diseases.A method for potentiating the plant disease-controlling effect of an aryl phenyl ketone fungicide, said method comprising using, together with component (a) that is the aryl phenyl ketone fungicide, at least one kind of component (b) that is selected from the group consisting of a nonionic surfactant, an anionic surfactant, a cationic surfactant, a vegetable oil, paraffins, resins and terpenes, etc.
