Ash Dieback Disease

Ash dieback disease or Chalara dieback of ash, is a disease of ash trees caused by the fungus Hymenoscyphus fraxineus. It was first confirmed in the UK in February 2012. The disease causes leaf loss and crown dieback and once infected a tree will usually die, often as a result of the infection weakening the tree so that it becomes more susceptible to attack by other pests and diseases.

Chalara dieback of ash has potential to cause significant damage to the UK's ash population as it has to ash populations in continental Europe. Experience there shows that it can kill young ash trees quite quickly, while older trees can resist it for some time until prolonged exposure, or another pest or pathogen attacking them in their weakened state, eventually causes them to succumb.

Ash dieback disease was first found in eastern England and since 2012 more and more sites across the UK have been confirmed. Following this a plant health order was made that prohibits all imports of ash seeds, plants and trees, and all internal movement of ash seeds, plants and trees.

Detailed information on ash dieback can be found on the Forestry Commission website

Ash dieback

Ash dieback on Exmoor  

Ash dieback is now widespread on Exmoor. If you see an ash tree that is showing signs of ill health the first step is to establish what might be the cause. This should be done using the Forestry Commission printable guide that shows not only the signs of ash dieback but also those associated with other pests and diseases.

There is no requirement to report or notify Exmoor National Park Authority or any other organisation if you think you have spotted ash dieback. However, you can report it using the Forestry Commissions Tree Alert web page. This can also be used to report other tree pest and disease sightings.

The Forestry Commission have also produced another publication Managing Chalara ash dieback in England. It includes information on how ash should be managed in both woodland and urban settings.

If you do have a confirmed infection of ash dieback in a tree you are not required to take any particular action.



  • Keep an eye on the tree as the disease progresses, and only prune or fell them if they or their branches threaten to cause injury or damage, for example if they are next to a public right of way or road and failure could cause harm to the user of the highway.
  • In low-density situations such as parks and gardens, you can help to slow the spread of the disease by removing and disposing of infected ash plants, and collecting up and burning (where permitted), burying or composting the fallen leaves. This breaks the fungus's life cycle.


  • Fell ash trees as a pre-emptive measure or because you think they might have ash die back. Not all trees die of the infection - some are likely to have genetic factors which give them tolerance of, or resistance to, the disease, which may prove beneficial to the future recovery of the ash population if allowed to remain.

If you would like further advice regarding ash dieback or have any questions regarding the above information, please contact us

Tel: 01398 323665