The experiments were conducted in the years 2000-02 in Garlica near Krakow and Lososina Dolna near Nowy Sacz (Poland) on the apple cultivars Florina, Novamac, and Witos. The date of primary infection by fungi causing sooty blotch was determined in unsprayed orchards. It was found that the date of infection was different for various regions under investigation. The infection occurred primarily in late June and early July. The earliest infection was recorded for the Novamac cultivar. In the Lososina Dolna area the infection occurred earlier due to higher relative air humidity and rainfall. The duration of incubation period was also diversified for cultivars examined in both locations. The shortest period (29 days) was observed for Novamac in Lososina Dolna, while the longest one (45 days) for Florina in Garlica. It was found that the earlier date of primary infection, the shorter incubation period