Chalara fraxinea is a serious disease of ash trees caused by a fungus called Chalara fraxinea, including its sexual stage, Hymenoscyphus pseudoalbidus. It is believed to have originated in Continental Europe.
Signs and Symptoms
The disease causes leaf loss and crown dieback in affected trees. Infection usually leads to the death of the tree. The leaf stages of C. fraxinea disease are best observed between August and September, after fully leafed out but before the onset of leaves changing color in the autumn.
Ash trees suffering with the C. fraxinea infection have been found widely across Europe since 1992. This includes trees in forests, in urban areas, and in nurseries. In February 2012 C. fraxinea was found in a consignment of infected trees sent from a nursery in the Netherlands to Great Britain.
C. fraxinea is now being treated as a quarantine pest under national emergency measures in Great Britain. Ash plants are prohibited from being imported into the United States for planting.