Dieback of ash crowns, dying branches and twigs initially with distinclty light brown, mostly lentil- or boat-shaped bark necroses, sometimes with minute pustules, later on totally brown. Brown stain of the wood often extending far beyond the bark-necrosis. Affects ashes of all ages, natural stands as well as afforestations.
Affected tree species
The actual dieback of ashes, widespread in large parts of Europe, is caused by the microfungus Chalara fraxinea, which has been discovered in 2006. As found out in 2013, it belongs as asexual stage to a species named Hymenoscyphus pseudoalbidus, which has been found to be indigenous in SE-Asia and has invaded Europe during the Ninties. In addition, several other microfungi are contributing to the disease (for instance Cytospora pruinosa. Biology, pathology, epidemiology and ecology of Chalara fraxinea is presently subject of intense research in many European countries.
Curative measures Hygienic measures; avoid afforestation with ashes or use plant stock, which has been repeatedly checked for freedom from Chalara fraxinea (continue this checks after planting 2 times a year!); in urban sites, hibernating leaf stipes can be removed from the soil, since there the infectious spores are produced in the following year.
Dieback of an ash
Bark necrosis (Hymenoscyphus fraxineus), with callus
Twig with necrosis in cross section: bark locally necrotic, wood showing intense discoloration
Hymenoscyphus fraxineus: leaf stipe with black stain
Leaf stipe with fruiting bodies of Hymenoscyphus fraxineus