Explore British trees
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Ash dieback, also known as Chalara dieback of ash, is a serious disease that is killing ash across Europe. Ash is a very important tree in the UK both ecologically and culturally so this disease is causing great concern about the damage it will do.
Ash dieback affects ash trees (Fraxinus excelsior) and is caused by the fungus Hymenoscyphus fraxineus (previously known by the names Chalara fraxinea and Hymenoschyphus pseudoalbidus). It blocks the water transport systems in trees causing leaf loss, lesions in the wood and on the bark and ultimately the dieback of the crown of the tree.
This disease was first described in Poland in 1992 and has since swept westwards throughout Europe. It was first identified in Britain in 2012 in nursery stock then in the wider environment in 2013 although it could have been in the country much longer.
The number of confirmed findings is continuing to increase and the distribution is reported by the Forestry Commission on a regular basis.
Young trees are particularly vulnerable and die quickly once they succumb. Older trees can be slowly killed by a yearly cycle of infection. Spread of the disease in the UK is most likely to be as a result of the planting of infected nursery stock and wood but wind borne distribution of the fungal spores also occurs.
There are several key signs to look out for on ash trees. All of these symptoms can also be caused by other problems, so final diagnosis should be made by an expert. Summer is a good time to look for symptoms as in autumn and winter, ash trees will naturally be shedding their leaves making it difficult to identify ash dieback.
We are at the forefront of the fight against ash dieback. From researching resistant strains to campaigning for better biosecurity, we are in a race against time. Find out how we are working in partnership with other organisations to safeguard ash populations for the future.
Read Forestry Commission Ash Dieback pest alert (PDF, 700 KB)
Download the Forestry Commission picture guide (PDF,0.3MB)
Find out more about how to identify ash trees and why it is so important to our woodland and wildlife from Malcolm Allen, Woodland Trust Site Manager for Cornwall and East Devon.
This video shows samples affected by ash dieback from The Food and Environment Research Agency.
If you think you’ve spotted this disease please inform the Forestry Commission using the Tree Alert reporting tool. Three good-quality digital photographs are required to aid identification.
For more information visit the Forestry Commission.