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Cyngor Sir Ynys Môn - Isle of Anglesey County Council

Ash dieback

Ash dieback is a highly infectious fungal disease of common ash (fraxinus excelsior) one of the commonest native tree species in Wales.

It caused by a fungus hymenoscyphus fraxineus (previously known as 'chalara') that originated from East Asia. First confirmed in UK in 2012, ash dieback has since spread rapidly throughout Wales.

Ash is frequently found in hedgerows and small woodlands along roads.

There is no known cure or clear method for stopping its spread.

Reporting symptoms

If you think you have spotted ash dieback on council land you can report this to us using our online form.

Ash is frequently found in hedgerows and small woodlands along roads.

It is important in the landscape and for wildlife, such as nesting birds and bats, supporting hundreds of other species.

It is likely that up to 95% of ash trees infected with the disease will decline and die over the next several years.

However, a small percentage (1-5%) may possess some tolerance to the disease; these trees will be important to the future survival of ash.

The main symptoms are leaf loss and wilting, resulting in dead twigs and branches known as ‘crown dieback’.

Trees infected by ash dieback are more easily identified during the summer (July to September) due to bare or dead branches (starting at the branch tips).

As the disease progresses, it kills the bark and trunk resulting in the death of the tree. Trees affected by ash dieback also become more susceptible to secondary diseases including honey fungus which can cause butt or root rot and can speed up the trees becoming hazardous.

Public safety is of serious concern to all owners of ash trees, particularly where they are growing within falling distance of a property, road or public space.

While The Highway Authority is responsible for the trees growing in the highway verge, trees growing along boundary hedgerows or on the field/garden side of boundary fences are the responsibility of private landowners.

Tree owners have a legal duty of care in respect of their trees and may be liable for damage/ injury to road and footpath users or neighbouring properties, caused by the failure of a tree or branch.

Landowners should therefore make sure that regular inspections of their trees are carried out (and recorded) to ensure they are healthy and without obvious defects that could present a hazard to others.

The rapid decline of infected ash makes annual surveys (during the months July – September whilst trees are in leaf) urgent as the dead wood in the crown is liable to snap off and potentially cause damage or accidents.

Where more than 50% of the crown has died back the tree may pose a risk to safety. It is currently recommended that at this stage, in areas where there is a risk to people, properties or infrastructure, the tree is made safe.

Roadside surveys

Since May 2023, the council have been carrying out roadside surveys of ash dieback (ADB) on trees within falling distance of the highway.

The surveys have identified nearly 3000 trees of various sizes on public and private land that will present a danger to the highway network and need to be removed.

Trees on council land have been marked with an X for felling works.

Road closures

There will be road closures for tree felling work in areas with the highest concentrations of trees. The road closures will either be at weekends or at night.

Road signage advising of the closures will be visible on affected routes and diversion signage will be in place during the works. Areas with lower numbers of trees will be carried out under traffic light restrictions.

The timing of the works has been planned to reduce noise and traffic disruption; nonetheless there will be short-term traffic disruption to people and businesses.

These works are necessary to ensure the safe passage of road users and we ask for the cooperation of the public and landowners while they are being undertaken.

Private land

Owners of trees on private land will receive letters requesting that they organise the removal of dangerous trees on their land.

Trees can support species which are protected in law, in particular nesting birds, bats and red squirrels (dreys)

Either undertake tree felling and pruning work outside the bird nesting season - not during the period 1 March to 31 August - or within these times only if it can be clearly established that nesting is not underway

For mature trees, consider pollarding ash trees at 2m height. This may be an alternative to felling. This way some of the tree’s wildlife value (holes for birds and bats and lichens on trunk) can be kept while minimising the risk of the tree’s failure.

If trees have features such as cracks, cavities/hollows, dense ivy growth, bats are more likely to be present. If suspected employ an ecologist or seek advice from Natural Resources Wales (NRW) as a licence will be required before felling or pruning works can proceed. See Legal Considerations.

A consent licence would also be required from NRW if a red squirrel drey is present.

If trees are growing in a protected site such as Site of Special Scientific Interest (SSSI) you will also need to obtain consent from Natural Resources Wales (NRW).

Plant new trees for the future. If trees need to be felled for safety reasons, reduce the ecological and landscape loss by planting replacement native species using the 3-2-1 formula: plant 3 saplings for the loss of a large tree, 2 for a medium tree and 1 for a small tree.

This list does not cover all potential wildlife issues.

If no symptoms or slight infection are noted then the trees should be retained but monitored annually.

Keep a written and a dated photographic record of monitoring visits and the condition of your trees.

Do not fell infected trees unless they pose a safety risk (or for timber production), dead and dying trees are good for wildlife.

Do not fell all ash trees assuming all will die anyway - there is evidence that a small proportion will be able to tolerate the disease and recover. Identifying and retaining disease resistant trees is of great importance for the future of ash trees.

If in doubt, a qualified arboriculturist should be employed for their advice. The Arboricultural Association or the Local Authority Highway department may also be able to advise.

Safety of operatives

Special care may be needed during felling or pruning operations as infected trees can react unpredictably due to the brittle nature of the dead wood. It is highly recommended that you employ a professional to carry out any work.

A precautionary approach to the health and safety implications for tree contractors managing or felling infected ash trees is advised, as the risks are not yet well understood. 


If you engage a contractor, they should be insured, qualified and provide a written quotation. The cost will usually depend on the complexity of the situation, whether Traffic Management is required and scale of the work.

It is recommended that you use contractors who are members of a professional body or part of the ‘Buy with Confidence scheme’.

Beware of contractors who approach you regarding your trees.


Any felling near a highway will require liaison with the ‘streetworks’ section of the Council's Highway Department.

Felling Licence

Following current guidance, if you intend to fell more than 5m3 in any calendar quarter you will need a felling licence. However, if the tree poses an imminent danger it may be exempt.

To find out more see NRW booklet Tree felling – Getting permission 

Protected sites and species

Obtain a licence or consent from NRW if protected species or sites involved (see above) Links for licences:

Protected sites 

Protected species 

Protected wildlife 

Tree Preservation Orders (TPO) and Conservation Areas (CA)

You should contact your local Planning Authority if your tree is protected by a tree preservation order or if you are in a conservation area.

The leaves and seeds of an ash tree.
A close up of leaves and bark affected by ash dieback.
A veteran ash tree.
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