The fungus Cercospora beticola Sacc. is the one of the most important pathogens on the sugar beet. The frequent application of fungicides with the same mode of action increase a risk of development of resistant strains of the pathogen. Occurrence of C. beticola resistant strains has been never researched in Slovakia. In this work, C. beticola isolates were collected from 10 localities of Slovakia and analysed for fungicide resistance in laboratory conditions. Nine fungicides with different mode of action were tested – trifloxystrobin + cyproconazole, kresoxim-methyl + epoxiconazole, azoxystrobin + cyproconazole, thiophanate-methyl + tetraconazole, thiophanate-methyl, prochloraz + propiconazole, picoxystrobin, tetraconazole, and difenoconazole. The results confirmed, that occurrence of fungicide resistance in C. beticola population was established in Slovakia. Different criteria of assessment of fungicide resistance (based on EC50 and on growth rate – inhibition percentage) showed slightly different results, but both criteria confirmed resistant C. beticola strains to thiophanate-methyl, picoxystrobin and difenoconazole. Fields with higher frequency of application of these fungicides significantly supported the development of resistant strains. Assessment of any C. beticola strains have not confirmed reduced sensitivity to active ingredients tetraconazole and prochloraz + propiconazole. The lowest level of risk of fungicide resistance was confirmed in the locality Oslany. It is very important to focus on anti-resistant strategy and reduce of using fungicides on localities, where the occurrence of resistant C. beticola strains was confirmed – Dolné Saliby (thiophanate-methyl and picoxystrobin) and Senec (picoxystrobin and difenoconazole).

Fusarium head blight (FHB) is a dangerous disease of cereals in case of yield losses and mycotoxin production. The aim of this work was to estimate the influence of used fungicides on species spectrum associated with Fusarium head blight (FHB). The study was realised in Slovakia on winter wheat by natural infection of FHB. The ears were sprayed with fungicides at beginning of flowering. After development of disease symptoms, fungicide efficacy was estimated, and Fusarium species spectrum were isolated and determined in laboratory. The fungicide efficacy against FHB achieved 60.2-88.3%. The highest effectivity was estimated by using of prothioconazole + tebuconazole and prothioconazole + fluoxastrobin, followed by dimoxystrobin + cyproconazole, metconazole, propiconazole + cyproconazole, and prochloraz + tebuconazole. F. graminearum was the most frequently isolated from the ears, followed by M. nivale, F. avenaceum, F. culmorum, and F. poae. Using of prothioconazole + tebuconazole, metconazole, prothioconazole + fluoxastrobin, and tebuconazole significantly decreased incidence of F. graminearum on infected ears. The incidence of M. nivale on ears was significantly increased by using of all fungicides in comparison with untreated control. The results suggest that the ear spraying by triazole fungicides could enhance the incidence of less susceptible Fusarium species in ears, especially M. nivale. The variability in fungicide efficacy of fungicides against FHB in agricultural praxis colud be affected besides multipathogen origin of FHB just by selective effect of fungicides on different Fusarium species.