In the present study, 20 sycamore maples (Acer pseudoplatanus L.) were evaluated on eight plots (160 trees) affected by sooty bark disease (SBD), caused by Cryptostroma corticale (Ellis & Everh.) P.H. Greg. & S. Waller in Northern Bohemia, Czech Republic. Mortality and presence of common pest taxa were assessed for each tree. Data were statistically evaluated using frequency and principal component analyses. The presence of C. corticale and Prosthecium pyriforme Jaklitsch & Voglmayr were positively related, with a significantly higher occurrence on dead trees. Rhytisma acerinum (Pers.) Fr. and Aceria macrorhyncha Nalepa were also positively related. However, the presence of Drepanosiphum platanoidis Schrank was not clearly related to the other evaluated taxa. Furthermore, C corticale was not present on Norway maple trees (Acer platanoides L.) growing on the plots. The results suggest that (i) the mortality of the sycamore was caused by C. corticale, while P. pyriforme was only an accompanying weak pathogen; (ii) R. acerinum, A. macrorhyncha, and D. platanoidis did not cause the mortality of the sycamore and their presence was not related to C. corticale infection; and (iii) planting more resistant maple species on sites susceptible to attack by SBD, particularly when stressed by drought, is recommended.

Since 2008, spruce bud blight (Gemmamyces piceae (Borthw.) Casagr.) has been spreading epidemically in forest stands of the Czech Republic’s Ore Mountains. This fungus, with a disjunct Holarctic range, injures buds, especially of Colorado blue spruce (Picea pungens Engelm.). Damaged buds do not sprout, and, in case of a stronger attack, the tree does not recover its assimilation apparatus and may die. Within the past few years, there has been a huge spread of this fungus throughout the mountain range. This paper summarizes the biology of G. piceae, its host plants, and presents the first findings from the massive outbreak of G. piceae. In 2015, an increase in damage was detected on Norway spruce (Picea abies (L.) Karst). The course of the G. piceae epidemic had been monitored in 25 permanent research plots over the course of 11 years. In the case of Colorado blue spruce, stands aged 10–60 years were attacked, with 60% of buds damaged on average. The intensity of damage to Norway spruce buds was around 25%. Norway spruce infestation varied significantly depending upon the age of the stand (GLMM: p < 0.01). In the age class of 31–60 years, on average 80% of individuals were infested. In older stands, only 42% of trees were infested, and no infestation was found in individuals younger than 15 years. In Colorado blue spruce, the distribution of the pathogen was continuous, whereby all individuals in the research plots were affected, and, with the exception of a few trees, the infestation was lethal or resulted in a significant reduction of the assimilation apparatus. The development of damage on Colorado blue spruce can be characterized as continuous growth.

In this study, the fruit bodies (pycnidial) colonization and spore presence of Sphaeropsis sapinea (Fr.) Dyko & B. Sutton on Scots pine ( Pinus sylvestris L.) trees in stands affected by long-term drought in the Czech Republic were evaluated. A total of 520 cones at four sites were evaluated every 1.5 months from June 2019 to December 2020. The pycnidia of S. sapinea in relation to colonization by subcortical insects in inner bark and wood, and wood-decaying fungi a total of 340 trunks at 17 sites during the autumn of 2020 were also evaluated. Pycnidial colonization of S. sapinea on cones was significantly higher at the site with the highest air humidity and significantly lower in the sampling periods of June 2019, August 2019, and November 2019, which were characterized by low precipitation levels. S. sapinea spore presence on cones was significantly higher at sites in Bohemia compared to those in Moravia, in sites with higher air humidity, and in three consecutive sampling periods in March 2020–June 2020. Pycnidial colonization of S. sapinea on trunks was significantly positively dependent on the colonization of subcortical insects in both inner bark and wood, but not with the colonization of wood-decaying fungi. The results of this study show a positive relationship between high humidity and colonization by subcortical insects in inner bark and wood with S. sapinea on Scots pine.

Although transfers and invasions of alien fungi and oomycetes to new environments have ecological and economic impacts comparable to those of plants and animals, their importance has so far been underestimated. Here, we compile accessible records of alien species from these two groups. Extensive research of data across literature, on-line databases, herbaria, and institutional and personal collections has resulted in the first list of alien and cryptogenic fungi and oomycetes for the present-day area of the Czech Republic. A total number of 352 alien taxa recorded in the period 1813–2022 includes 38 archaeomycetes (i.e. species introduced into Europe before 1492), 310 neomycetes, and 4 unranked species. The highest proportion of alien fungi and oomycetes originated from North America, Europe, and temperate Asia. From the taxonomic point of view, ascomycetes represent the highest proportion of alien species, while at the class level, Peronosporomycetes , Dothideomycetes , Leotiomycetes , Pucciniomycetes , Sordariomycetes , and Agaricomycetes are the most frequent. Plant parasites prevail, whereas saprotrophic fungi are less numerous and other ecological groups are rare: six mycorrhizal fungi and two wild animal parasite species have been recorded in the Czech Republic. An assessment of potential risk indicated that numerous species impact (in order of frequency) horticulture, agriculture, and forestry. We identified 56 casually introduced species, 156 naturalised taxa, and 72 invasive species. Significant ecosystem damage may be expected for 36 introduced species, six of which can be classified as transformers. Five species were classified as eradicated. The terminology used in invasive plant and animal biology was adopted, with minor modifications to reflect the specificity of fungi and oomycetes. Natural and geopolitical conditions are discussed and taken into account in the proposed general scheme of invasions of fungi and oomycetes representing an integral part of neobiota and sharing invasion principles and rules with alien macroorganisms.