Chalara dieback of ash is a serious disease of ash trees caused by a fungus called Chalara fraxinea (C. fraxinea). The disease causes leaf loss and crown dieback in affected trees, and usually leads to tree death. It is believed that the disease may have been introduced into Ireland through the imports of ash plants and wood, including firewood, from continental European countries.
- Diseased saplings typically display dead tops and/or side shoots.
- At the base of dead side shoots, lesions can often be found on the subtending branch or stem.
- Lesions which girdle the branch or stem can cause wilting of the foliage above.
- Mature trees affected by the disease initially display dieback of the shoots and twigs at the periphery of their crowns. Dense clumps of foliage may be seen further back on branches where recovery shoots are produced.
- In late summer and early autumn ( July to October), fruiting bodies of Hymenoscyphus can be found on blackened rachises (leaf stalks) of ash in damp areas of leaf litter beneath trees. These do not necessarily belong to the pathogen but can be tested to determine their identity.