When used in admixture with mancozeb, chlorothalonil, a copper salt, folpet, fluazinam or cymoxanil (it being possible for the latter to be used also together with one of the other five components), metalaxyl having a high R-enantiomer content of more than 70% by weight, or pure R-metalaxyl, exhibits a markedly increased fungicidal action against plant diseases as compared with a similar mixture in which metalaxyl is used in the form of the racemate.