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Dieback on Ash - Chalara fraxinea

25 November 2009 Last Updated on                                              

15 December 2010 Adam Owen

Tree affected with Ash Dieback

A new disease causing tree mortality has increasingly been observed in European countries on ash trees (Fraxinus excelsior) during the last ten years. The first studies revealed the presence of a pathogenic fungus which was described as a new species, Chalara fraxinea. Because ash dieback could represent a serious threat to forest, amenity and nursery ash trees, the EPPO Secretariat decided to add C. fraxinea to the EPPO Alert List in 2007.


Further studies carried out in 2008 in Poland revealed that C. fraxinea was the anamorph of an already described species, Hymenoscyphus albidus, which is considered as non-pathogenic, native, and widespread in Europe. Therefore, the emergence of a new disease caused by this species is difficult to explain, and it is acknowledged that further studies are needed to better understand the taxonomy and biology of the H. albidus/C. fraxinea complex.


© European & Mediterranean Plant Protection Organization


For more information visit the EPPO website.