Pest or disease?

Causal agent:
Hymenoscyphus fraxineus (fungus)

Host species:
Ash, with European ash being very susceptible

Present in the UK?

Tree Alert required?
Only required if found in an empty square on this map.

Chalara ash dieback, often called just chalara or ash dieback, is a disease of ash trees.

Chalara has had a large impact on the UK’s ash trees. The disease was first recorded in the UK in 2012 and has since spread to most of the country. It infects trees of all ages. The fungus grows inside the tree, blocking the essential water and nutrient transport systems, which is often fatal. The prevalence of this disease has caused significant losses of our ash trees.

Chalara causes characteristic diamond-shaped lesions on the branches and stem of the tree, these tend form around the point that a shoot or branch joins the trunk. Other symptoms include wilting of leaves and shoots and dieback of branches. Later in the season, the small, white, cup-shaped fruiting bodies of the fungus can be seen in the leaf litter around the base of the tree. For more information on chalara please see the resources below.