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What is it?

Ash dieback is a fungal disease called Hymenoscyphus fraxineus (formally Chalara Fraxinea) found in ash trees that carries a high mortality rate. Ash trees in the UK have little resistance to this disease as it was imported from Asia meaning UK trees did not develop natural resistance. The disease is airborne and can travel far before landing on a tree and causing infection. Due to this, the spread of the disease has happened very quickly throughout the UK.

Where is it?

Ash dieback is affecting trees across the whole of the UK and Europe. The fungus causing the disease was first identified in 2012 though it has been affecting trees in the UK since at least 2006.

What MCC are doing to tackle ADB?

Monmouthshire County Council will aim to keep as many ash trees as possible where it does not affect the safety of people or infrastructure. As a general guideline, only once a crown has reached roughly 50% dieback will it then be considered for removal. Though this decision is made on a case-by-case assessment method.

How can I tell if a tree has it

Ash dieback can present and progress differently tree to tree. A tree suffering from ash dieback may have one or all the following symptoms:

  • Crown thinning
  • Brown leaves that turn and drop before the end of summer, particularly evident at the ends of branches
  • Lesions on the stems (particularly in young trees)
  • Seeds/keys will turn brown but remain on the branch

Ash trees are usually the last species of tree to flush (grow new seasons leaves) so do not be alarmed if an ash tree has not regrown it’s leaves during springtime. Ash trees should have a full crown by mid-June.

Managing ash dieback

Although ash dieback is deadly for most trees, the presence of the disease is not grounds for removal. Some trees may survive leading to a stronger genetic resistance for the next generation of ash trees. Ash trees with dieback will be monitored for health and safety reasons and only removed in cases where the risk has been assessed as unacceptable. Pre-emptive removal of ash trees will not slow the spread as it is airborne and could prevent potentially resistant trees being found. Additionally, dead and dying trees provide good habitats for wildlife thus encouraging biodiversity.

What can I do to help?

If you own ash trees, the best course of action is to keep a written and dated photographic record monitoring their condition. Additionally, if you frequently visit forested areas make sure you clean your shoes in between forest sites and always park on hard standing rather than grass where possible.

Report ash dieback on council land

If you feel you have positively identified a case of ash dieback on council land then please report either via the My Monmouthshire webpage or by contacting the Council Tree Officer (Operations). If you are unsure who the tree belongs to please see our Specific tree concern page.

Trees on private land affected by Ash Dieback

Protected trees

If you need to cut or fell diseased ash trees on your own land, before undertaking any work on trees you should check whether they are protected by law and if permission is needed. Ash trees that are under a Tree Preservation Order (TPO) or within a Conservation Area will require a formal application to be submitted to the Local Planning Authority to gain consent

See our page on Tree Preservation Orders for more information

Felling Licence (Forestry Act 1967) may be needed if you are proposing to cut down a number of trees. Additionally, if the trees are within a protected area, for example a Site of Special Scientific Interest (SSSI), you will need consent from Natural Resources Wales (NRW). More information about getting permission to fell trees can be found on the NRW website

Tree works next to the highway

Ash dieback causes the timber to become brittle, making tree felling and other cutting unpredictable and more hazardous. For this reason, it is especially important to have proper safeguards in place and for such work to be carried out by suitably qualified and experienced operatives.

To ensure the safety of the public and those conducting the work, any tree works adjacent to the highway should be carried out by competent people with appropriate traffic management measures in place. Those carrying out the works must contact Monmouthshire County Council Highways department at the planning stage by emailing

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