A new disease affecting Ash trees has recently been found in Britain. The disease has already caused extensive loss of Ash trees in mainland Europe, and is potentially a major threat to Ash trees in the UK.
If you think that you have identified Chalara fraxinea on an Ash tree, then you should contact the Forestry Commission.
Ash dieback disease is caused by the fungus Chalara fraxinea and was found in the UK for the first time earlier this year in young Ash plants in tree nurseries and recently planted sites. The disease is characterised by the premature loss of leaves from the outer parts of the crown (top and sides), accompanied by long diamond-shaped lesions or areas of sunken and discoloured bark on twigs. These lesions girdle twigs and small branches, starving the leaves above of water and nutrients and causing whole branches to die. In mature trees, it is the new growth that is affected.
The government has implemented a ban on the import of Ash plants into the UK and on the movement of Ash plants, seeds and trees into and around the UK. The ban does not extend to the movement of ash timber or firewood except from sites where the disease has already been found.
The Forestry Commission have produced the following video showing how to identify the disease.
Note that because one of the symptoms of Chalara fraxinea is leaf loss, identification of the disease will be difficult in Autumn when the trees are losing their leaves.