Chalara fraxinea (Kowalski)
Significance: A recent article in the publication Forest Pathology describes a new species in the genus Chalara, named C. fraxinea, that has frequently been isolated from the stems, branches, and sometimes roots of wilting and dying European ash, Fraxinus excelsior, trees in Poland.
According to the report, intensive dieback of ash was first observed about 10 years ago in the north-western part of Poland, but today is widely distributed throughout the country. Initial symptoms include necrotic spotting on stems and branches followed by wilting of leaves, top-dieback of branches and eventually death of the entire tree. Trees are dying in all age classes, irrespective of site conditions and regeneration methods. The newly named fungus has been isolated from a large percentage of diseased shoots as well as from dead roots attached to living trees, and current studies have confirmed an association between the fungus and the disease.
The author indicates that there are approximately 120 described species in the genus Chalara, including many which are anamorphs of ascomyceteous fungi (e.g.Ceratocystis species). Some research suggests this newly described species may be closely related to those that have a Ceratocystis perfect state, but so far no teleomorph has been observed in the laboratory or in nature.
Issues of Concern: It is not known if this species is more widely distributed in parts of Europe (or elsewhere) or if it poses a treat to other ash species, such as our 16 native North American species. Based on the information presented in this article, the fungus could become a significant pathogen of European ash outside of the infested area in Poland and also presents a potential threat to other ash species. Further studies on the pathogen's host range and general biology are needed.
Pathways: No vectors have been identified but since the fungus is found on shoots, branches, and sometimes roots, and in trees of all age classes, movement of nursery stock would be a likely pathway for spread of the fungus.
Kowalski, T. 2006. Chalara fraxinea sp. nov. associated with dieback of ash (Fraxinus excelsior) in Poland. Forest Pathology Vol. 36:264-270.