Root rot fungus (Heterobasidium annosum)

Forest pathological surveys conducted by the Forest Protection Stations – Sofia, Plovdiv, Varna indicate that in the windthrow-affected stands in the specified regions, as well as in most of the spruce stands and plantations on Vitosha, infestations by the root rot fungus (Heterobasidium annosum) are also observed. This fungus develops in the heartwood of spruce, fir and Macedonian pine over the course of several decades, reaching a height of 7–8 m, in some cases even greater, without any visible external symptoms. During strong, extreme winds or heavy wet snow, the stems break at the height corresponding to the development of wood decay caused by the fungus.

In recent years, the total infested area has been increasing most rapidly in the regions of the Regional Forest Directorates Kyustendil, Blagoevgrad and Sofia. Sanitary felling is planned in these stands and plantations. An increase in the area and intensity of infestations by this fungus can be expected in coniferous stands aged 30–40 years in the western Rhodopes, established on former agricultural lands, as well as in the mature spruce forests of Vitosha, Pirin and Rila.