THE PRESENT INVENTION PROVIDES: A COMPOSITION FOR CONTROLLING PLANT DISEASES COMPRISING, AS ACTIVE INGREDIENTS, 4-OXO-4-[(2-PHENYLETHYL) AMINO] -BUTYRIC ACID AND A QUINONE OUTSIDE INHIBITOR; A METHOD FOR CONTROLLING PLANT DISEASES WHICH COMPRISES APPLYING EFFECTIVE AMOUNTS OF 4-0X0-4-[(2-PHENYLETHYL) AMINO]-BUTYRIC ACID AND A QUINONE OUTSIDE INHIBITOR TO A PLANT OR SOIL FOR GROWING PLANT; AND SO ON.