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The forest area infected by mistletoe (Viscum album L.) in Europe has been increasing in recent years. The highest potential threat is posed by Viscum album subsp. austriacum, a parasite of Pinus sylvestris, and V. album subsp. abietis, a parasite of Abies alba. The paper presents a literature review related to biology, ecology and possible methods of limiting the negative impact of mistletoe on forest management. The vast majority of studies indicate that the presence of mistletoe negatively affects the growth as well as defensive and reproductive capabilities of trees. Due to the wasteful water management of the parasite, infected trees are particularly vulnerable to weakening during periods of drought. Mistletoe is a heliophilous taxon and forest breeding treatments should reduce light intensity in the forest canopy. Foresters should resign from leaving individual and group seed trees in forest stands inhabited by mistletoe after the cuts, because they may be a source of seeds for the parasite invasion to the neighboring stands. The most effective method against mistletoe is cutting out the infected trees. However, removal of individual trees in forest stand may be difficult, because the most often they are the dominant and hence the most vulnerable trees in the forest management. Mistletoe is also noticeable when the number of infected trees is already very large and they cannot be removed without disturbing the stability of the forest stand. Therefore, there is an urgent need to develop methods for monitoring stands for early detection of threat. Remote sensing methods can be very useful. It is also necessary to develop management strategies with mistletoe infected stands.
The work concerned the ascomycetous fungus Eutypella parasitica, which for several decades has been present in North America, where it attacks various species of maple. In 2005, for the first time it was recorded in Europe, in Slovenia. Later on it was found in Austria, Croatia, Germany, Hungary and the Czech Republic. In 2016 for the first time the species was reported in Poland, in the Polish−Czech border region. The work includes fieldwork and laboratory research on disease symptoms and the causal pathogen. The research was conducted in August 2016 in the Ustroń Forest District. In 16 randomly selected stands, the health of Acer spp. trunks was analyzed, especially in terms of Eutypella parasitica infection. Of the 16 trees, where extensive necrosis and cankers were found, the material was collected for laboratory analyses. In the laboratory, the fruit bodies of fungi on necrotic lesions were examined and the fungi isolates were performed on 2% malt−agar extract. Identification of representative E. parasitica isolates was confirmed based on the ITS rDNA sequence. Within the 16 stands, where the maples were analyzed, individuals with symptoms of trunk infestation by E. parasitica were found in 8 stands. Based on in situ produced fruiting bodies and isolated cultures, the presence of E. parasitica was finally confirmed on 14 trunks, including 13 Acer pseudoplatanus trunks and one A. campestre. All cankers were located in the butt section of the trunk, below 3 meters, reaching from 21 to 252 cm in length. Fungal fruit bodies were present within the necrotic lesions. Morphological characteristics of asci, ascospores and colonies isolated on malt−agar extract are given. The phytosanitary risk for Acer pseudoplatanus and other maples is also discussed. Moreover the preliminary actions that should be taken by the foresters are indicated.
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