Common name Ash dieback
Scientific names Hymenoscyphus fraxineus (sexual stage), Chalara fraxinea (asexual stage)
Plants affected Fraxinus spp especially F. excelsior and F. angustifolia
Main symptoms Necrotic lesions in the bark and xylem, crown dieback of trees, leaf loss
Caused by Fungus
Timing Spores active June to October
What is ash dieback?
Ash dieback is a serious disease of ash trees, caused by a fungus now called Hymenoscyphus fraxineus. The fungus was described as a new fungal species in 2006 as the cause of ash (Fraxinus excelsior) mortality in European countries during the previous ten years.
The disease affects trees of all ages. Young trees can be killed in one season and older trees tend to succumb after several seasons of infection. It has spread rapidly in continental Europe. In the UK, the disease was first confirmed in trees growing in nurseries or on recently planted ash trees. However, many cases have now been confirmed in the wider environment in the UK and the disease is widely distributed. The latest distribution maps for cases of the disease in the wider environment can be found on the Forestry Commission website.