In the years 1999-2001 we observed the spread and harmful effects of pathogenic fungi causing the dying of some grass species in permanent grass growths. The most common and frequent cause of the dying (winter freezing injury) is the fungus Microdochium nivale known also as Fusarium nivale, or Gerlachia nivalis (imperfect stage) - snow mould. The evaluation was carried out in dominant species (Deschampsia cespitosa, Festuca rubra, Holcus mollis) in permanent grass growths in the central part of the Bohemian Forest (locality Zhůří (1050-1080 m a.s.l.). The experiment involved three treatments: (1) Mulched growth (mulched only once), (2) Unharvested growth (fallow land) and (3) Mown growth (mown once in a year). The phytopathological evaluation took place during the vegetation periods in of 1999-2001 at three particular times (May, June, July). Our investigation has shown the most considerable development of the fungi of the genus Fusarium in the unharvested growth with serious decline of Festuca rubra, which deteriorates the conditions for subsequent fodder crops. On the other hand, the mown growth showed the least extent of fungi-attacked dominant grass species. The least occurrence of harmful Fusarium sp. div. disease (fusariosis) was found in Deschampsia cespitosa whereas the most serious damage occurred in Festuca rubra. From the viewpoint of temporal dynamics of fungal disease, the increase took place at the beginning of the second (1999) and first (2000, 2001) decade of May. In the tested dominant grasses we determined the genus Fusarium as the cause of fungal disease. Apart from further undetermined species, Microdochium nivale and Fusarium solani were the most frequent species.