Hysterographium - dieback of ashes
Fig. 1. Hysterographium fraxini, fruiting bodies
Hysterographium fraxini is an ascomycete producing small black fruiting bodies which are visible by the naked eye. To recognize their typical morphology requires the use of a good hand-lens. The fruiting bodies are tiny (around 1 mm or less) erumpent, black, elongated (straight or slightly bent) and bulging showing a longitudinal slit (hysterothecia, Fig.1). They are arranged in small groups on the surface of dead ash-shoots, twigs and branches.
On ashes in natural habitats, usually in dense young stands.
Commonly a saprophytic species, it can cause dieback mostly of lower branches, which suffer from light deficiency. Predisposing factors are various types of stress: frost, wet soil, permanent high humidity, frequent change of dry and wet periods, nutrient deficiency, damage by insects or any wounds.
It causes dieback of especially young ashes, sometimes even crown dieback of mature trees. However, usually ashes are not damaged severely.
None, if the characteristic fruiting bodies are present. Otherwise other causes of dieback, but most of all by Hymenoscyphus fraxineus.