Ash dieback is caused by the fungus Hymenoscyphus fraxineus and is commonly referred to as Chalara ash dieback. Once a tree is infected the disease is usually fatal. The disease can kill a tree host directly through the actions of the pathogen, or indirectly by weakening it to the point where it succumbs more readily to attacks by other pests or pathogens. Ash dieback only affects ash trees (Fraxinus spp.) and ash trees of all ages can be affected.
