One hundred cucurbit powdery mildew (CPM) isolates (41 Golovinomyces orontii s.l. [Go], 59 Podosphaera xanthii [Px]) from the Czech Republic (2012 to 2015), were screened for fungicide efficacy to the six frequently used fungicides (quinoxyfen /Atlas 500 SC/, propiconazole /Bumper 25 EC/, fenpropimorph /Corbel/, dinocap /Karathane LC/ azoxystrobin /Ortiva/) and penconazole /Topas 100 EC/). Fungicide efficacy was determined by a modified leaf-disc bioassay with three concentrations. Highly susceptible Cucumis sativus ‘Stela F1’ was used for preparation of leaf discs. Efficacy of fungicides towards screened CPM isolates varied significantly. There were observed also differences in efficacy of some fungicides between both CPM species, and as well as, among years. In the case of quinoxyfen, propiconazole, fenpropimorph and penconazole, there have been no reports from Czech Republic since the year 2012. Fenpropimorph was 100% effective and showed some phytotoxicity to C. sativus ‘Stela F1’ leaf discs. Propiconazole was also highly effective; the same phenomenon was recorded for penconazole, however only for Go during the studied period. Nevertheless, efficacy of penconazole has decreased since 2014 when frequency of Px strains with moderately resistant reactions to the lower and recommended concentrations increased. The highest number of various reaction patterns of CPM populations was observed in response to quinoxyfen. There was recorded decreased efficacy, except the year 2015, when a majority of CPM isolates were controlled by recommended concentration. Dinocap showed high efficacy and the majority of screened CPM isolates expressed sensitive reaction to recommended concentration. However, there were also observed occurrence of strains (Go, Px) with moderately resistant or resistant responses to screened concentrations. This phenomenon reflects the situation in Czech CPM populations from 2001 to 2011. Azoxystrobin showed low efficacy, this situation started in 2007 (1st year of study), when a continual shift towards prevalence of azoxystrobin-resistant strains in Czech CPM populations was observed (Lebeda et al. 2010a,b; Sedláková et al. 2017).