The spatial distribution and niche differentiation of three closely related species (Erysiphe alphitoides, E. quercicola and E. hypophylla) causing oak powdery mildew was studied at scales ranging from the European continent, where they are invasive, to a single leaf. While E. alphitoides was dominant at all scales, E. quercicola and E. hypophylla had restricted geographic, stand and leaf distributions. The large-scale distributions were likely explained by climatic factors and species environmental tolerances, with E. quercicola being more frequent in warmer climates and E. hypophylla in colder climates. The extensive sampling and molecular analyses revealed the cryptic invasion of E. quercicola in nine countries from which it was not yet recorded. The presence of the three species was also strongly affected by host factors, such as oak species and developmental stage. Segregation patterns between Erysiphe species were finally observed at the leaf scale, between and within leaf surfaces, suggesting competitive effects.

Summary The occurrence and distribution of Dothistroma needle blight (DNB) were studied in 2014–2017 around Slovakia. A total of 84 localities, both native and planted, were investigated, and the presence of DNB was confirmed in 73 of them. In all positive locations, symptoms typical of DNB were observed and the Dothistroma species was confirmed using species‐specific primers either from fungal cultures or directly from needles. Both Dothistroma species—D. septosporum and D. pini—were identified. Both species occurred together in 29 locations, only D. septosporum in 42 and only D. pini in two locations. The host range of D. septosporum included 10 pine species and two spruce species. The host range of D. pini comprised the same number of pine hosts but only one spruce species. Five pine hosts, P. aristata, P. coulteri, P. densiflora, P. jeffreyi, P. × schwerinii, and one spruce host P. abies are new hosts species of D. pini. P. densiflora and Picea pungens have earlier been reported to be susceptible for DNB. In this study, D. septosporum was found from both tree species.

The diversity of fungi on branches and leaves of ashes (Fraxinus angustifolia, F. excelsior, F. ornus) in Slovakia was studied. Symptomatic material collected in Slovakia during the period of 2013 to 2017 and herbarium specimens previously collected were examined. In total, 30 fungal taxa (15 Deuteromycetes, 14 Ascomycetes and one Basidiomycetes) were recorded. Twenty-three of them have never been recorded on ashes in the country. The most frequently occurring fungi were Hymenoscyphus fraxineus (anamorph Chalara fraxinea) that causes necrosis of shoots and branches, and Phyllactinia fraxini, a foliar pathogen that causes powdery mildew disease. Fungal diversity on ashes growing in different types of stands was compared. Species richness was the greatest in seed orchards (20 fungal taxa) compared to private gardens, which contained the lowest (two fungal taxa). Species diversity in forest stands comprised 18 fungal taxa and the urban greenery was represented by 10 fungal taxa. Nine fungal taxa were recorded in tree alley along the road. The widest fungal species spectrum was recorded on F. excelsior.