Chalara fraxinea incidence in Hungarian ash (Fraxinus excelsior) forests

Abstract

Chalara fraxinea was identified for the first time in Hungary in the first half of 2008, in western Hungary near Kapuvar and Sarvar, in 4 to 6 years old mixed (seed and coppice shoot) origin European ash (Fraxinus excelsior) stands (Szabo, 2008). In the same time in Budapest, under an older Turkey Oak – Sessile Oak – European ash stand we also detected the symptoms and the pathogen on the saplings of the natural regrowth. The local foresters first thought, that the wilting was caused by the frost, but in that period of time there were no frosty days. With the typical symptoms and the examinations of the collected samples, we were able to definitely identify the Chalara fraxinea as pathogen (Szabo, 2009). This pathogenous fungus was also identified on Narrow-leafed ash (Fraxinus angustifolia), from the samples of the western part of Hungary (Kirisits et al., 2009). In 2008-2009, we thoroughly researched the distribution of the pathogen in Hungary, and the volume of the caused damages. As a result, we confirmed that the pathogen spread to the whole area of Hungary (Figure 1). It appears both in young and older stands, but it causes damages more frequently in 2 to 10 years old forestations. Because of the characteristics of the symptoms and the measures of the dieback, we concluded that the pathogen appeared in Hungary 2 to 3 years before. The degree of the infections in the examined forest stands is significantly diverse. The most severe infestation was observed in Eastern-Hungary, near Debrecen, in the summer of 2009. This European ash stand was 10 years old, with 0.5 ha of area, and was planted with 2 years old saplings. Every single tree showed the symptoms of C. fraxinea infection (Figure 2). In the examined part of the forest-stand, the mortality reached 37%. Among the still living trees, the rate of the infected and died stem parts varied between 20 to 90%. From the symptoms of the dead trees we diagnosed, that the first infections in this area also occurred a few years ago. We do not know much about the environmental conditions assisting the infestation. The examinations of the infested forest-stands of Western-Hungary show that the infestation is more frequent on sites with frost-hollow, deep soil and plenty of water. In the same time we also noticed that the symptoms are also frequent on forest sites drier than average and exposed to extreme cold (Szabo et al., 2009).According to the surveys, the fungus is more common in younger stands, but this can be affected by the fact, that we have lesser amount of samples from older and bigger trees, for collecting samples and identifying them from large crowns is more difficult. After the survey in Bukk-mountains, North-eastern-Hungary, we found that the extent of the infection is at least the same on older or middle aged trees, than on the youngest ones. Contrarily, in the western part of the country in mixed species forest stands we experienced mass and severe infections of the natural ash regrowth, while older trees showed only small degree of typical symptoms in their crowns. The complete death of older trees takes more time, so major mortality occurs on young ones, 2 to 10 years old trees. In August, 2009 we surveyed the degree of C. fraxinea infestations in some forestry’s of the Bakony-mountains, in different aged and in different tree-species composition forests. Based on this survey we pointed out that in the significant majority of the surveyed stands the rate of infected ash trees is under 5%, and in only 2 forest-parts are there 5 to 10% infestations (Table 1). Key words: Chalara fraxinea, ash dieback, Fraxinus excelsior, Hymenoscyphus pseudoalbidus.