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In order to minimize the risk of spreading Phytophthora species to forests and ornamental sites via nursery stock, BFW has been performing checks of plants of Common Alder (Alnus glutinosa) and European beech (Fagus sylvatica) from forest nurseries for contamination with Phytophthora spp. on a service-basis for the past 13 years. Following a scheme developed by BFW, samples (both plants and soil) are taken by BFW-technicians preferably most close to the time of selling. The samples are tested in BFW’s lab by direct isolation from symptomatic plant tissues and by soil baiting. Identification of species is performed by morphological and molecular methods. The results (identified species of Phytophthora) are delivered to the nurseries and, in case of freedom of the samples from Phytophthora, a certificate is issued to state that the tested material was not contaminated. In order to push to a stable production of plants not infested by Phytophthora, the nurseries are informed on a range of requirements. To produce an international protocol for both a Phytophthora-testing-system and a guideline for nurseries to enable a stable guaranteed freedom of plantstock from Phytophthora, a questionnaire was produced in collaboration with nurseries in Austria to define the most essential challenges. The outcome is a list of prerequisites ranked by importance, reliability and practicability. Among the requirements, avoidance of introduction of Phytophthora’s into the nursery via plant import on the one hand and the need for irrigation of the plants with non infected water turned out the most essential challenges. As a preliminary result we can state that, regarding the spectrum of nurseries in Europe with respect to dimension, financial potential, but also availability of irrigation sources as well as infection-risks by specific environments, an international management guideline will have to comprise a certain flexibility to achieve Phytophthora-free plant production. Ash dieback monitoring has been performed since 2008 on 14 sites distributed throughout Lower Austria. Common ash (Fraxinus excelsior) is present on 13 plots while one plot represents a pure stand of Narrow-leaved ash (Fraxinus angustifolia). Assessment of the disease performed on a yearly base results in a health status of the trees in a 5% scale, reaching from 0% (no dieback symptoms in the crown) to 100% (crown dead). After ten years of continuous monitoring, data for 186 F.excelsior and 17 F.angustifolia trees in twelve different sites situated in Lower Austria are available. In the past few years, ash dieback has turned out to be a big problem for forest owners and the risk of trees losing their stability without showing symptoms of a disease in the crown raised the awareness and resulted in massive clear cuts and felling of single ash trees. Therefore, the total number of 280 trees in the year 2008 was reduced to 186 F.excelsior trees and 17 F.angustifolia trees in 2018. Within this time, mean crown dieback intensity of the remaining F.excelsior trees increased from 12% to 31%. Distribution in damage classes is as follows: 38% (up to 10%); 21% (> 10% - 25%); 12% (> 25% - 50%); 16% (> 50% - 90%); 5% (> 90% < 100%) an 8% (100%) of dieback in the crown. However, crown dieback damage varies among the plots at the different sites. While in the healthiest plot all trees show less than 25% of crown damage, with 79% even less than 10%, in the plot with the highest disease intensity a majority of trees exhibits more than 50% of crown damage and the mortality level increased to 40% by the year 2018. Although F.angustifolia is as susceptible as F.excelsior, the single plot representing this species remains relatively healthy by 2018 and mean crown damage of the 17 remaining trees was 3%. This high variation of mean crown damage among the tested plots is likely due to differences of infection pressure, forest site condition and tree size/age. Future work will contain analysis of this long-term observation of crown damage in relation to climatic data. Ash dieback has recently been connected with a high security risk, and reports of ash trees falling down or being thrown have increased throughout Austria. Consequently, forest owners started to cut trees in order to minimize the danger. Therefore, we started to investigate the relationship between visually detectable symptoms caused by Hymenoscyphus fraxineus (including secondary pathogens) on tree stability. In a mixed F.excelsior stand in Lower Austria, affected by crown symptoms and basal lesions, a practical survey was performed in October 2017. Twenty trees were chosen and the occurrence of crown symptoms, basal stem lesions and secondary pathogens documented. Trees were then pulled over with a tractor mounted winch. By aid of a hanging scale, integrated into the pull rope, the tractive force applied to the trees was measured. The type of fraction (root or stem) was documented. Further, the size of the root system and the condition of the main roots were assessed. The samples collected for further analysis in the laboratory included root tissue, life stages of secondary pathogens as well as a stem disc of the basal part of each tree trunk. Preliminary results show that the relation between crown damage and the affected necrotic stem circumference is weak and both symptoms have to be considered separately in assessing tree health. The diameter of tree trunks had a significant impact on the maximum tractive force required to pull trees over. Results of the root assessment and the analysis of stem disks showed that there is a relation with rot in the stem and especially with root rot caused by Armillaria sp. Trees with visible demarcation lines in the stem discs were more affected by basal lesions and rot. Assessment of disease symptoms of ash trees affected by H.fraxineus should include a careful inspection of the tree base, especially on sites where Armillaria sp. are present. This first trial shows that inferring on the stability of ash trees makes it necessary to combine the occurrence of basal lesions caused by H.fraxineus and root rot caused by secondary pathogens. |
