Alert Section

Ash Dieback

Ash dieback is the most significant tree disease to affect the UK since Dutch elm disease.It has the potential to infect more than two billion UK ash trees and lead to the death of approximately 90% of them.

Ash dieback is now widespread in Flintshire and as a result there are significant safety implications for the council and landowners where ash trees are situated near to people or property.

In response to the disease’s threats the council has produced the Flintshire Ash Dieback Action Plan.

Landowners must make themselves aware of the disease and its effects. 

Ash Dieback 

Ash dieback (Hymenoscyphus fraxineus) is a fungal pathogen that affects the UK’s native ash tree (Fraxinus excelsior) and is likely to kill approximately 90% of them.

Ash dieback was first confirmed in Flintshire in 2015 and is now widespread affecting ash trees of all ages. Young trees are usually killed over a period of several months whilst mature trees decline over several years. Following initial infection by ash dieback mature trees are likely to be subject to secondary infection by other pathogens.

Mature trees may respond to the infection with dense clusters of leaf growth that mark the extremities of the live tree. This dense growth can be likened to a cheerleader’s pom-pom and a clear symptom of ash dieback in a mature tree. Where the disease is fatal the dieback progresses until there is no foliage on the tree. 

Although devastating ash dieback is not always fatal. Evidence from mainland Europe suggests that 10% of trees exhibit moderate tolerance and 1% to 2% have a high level of disease tolerance.

The Tree Council and the Forestry Commission have online resources for the disease’s identification.

Forest Research – Chalara Ash dieback

The Tree Council – Chalara in the UK

The Tree Council – Chalara in the UK: A photo ID guide to symptoms in in larger trees

Safety concerns 

There is an increased risk to public safety as a result of mature ash trees dying back and subsequently falling or shedding large limbs. 

Due to its predominant limestone geology common ash is one of the most abundant and widely distributed trees in Flintshire. Ash is estimated to be the dominant tree species in 1500ha of the county’s woodlands and present in another 400ha. 

It is estimated that there are 12,000 ash trees over 5m tall growing adjacent to the county’s main roads.

Landowners are under a duty of care which extends to cover the management of trees and is why they are advised to have trees regularly inspected (and keep records) if they are located where, if they failed, they could cause harm.

Managing trees for safety is a leaflet aimed at householders produced by the National Tree Safety Group.

The Arboricultural Association has also published Ash Dieback Guidance for landowners.

Trees adjacent highway

The greatest liability is considered to be the mature ash trees adjacent to the principal A Roads and B Roads of the county’s highway network, where vehicles are travelling the fastest and typically carry the most traffic. In addition there are the mature ash trees adjacent minor roads in urban areas which are used extensively by vehicular traffic, cyclists and pedestrians.

Caution Ash Dieback Surveying

In response to the increased risks that ash dieback presents the council is increasing the frequency of highway tree surveys to identify hazardous trees on main routes. These surveys will primarily focus on trees within the public highway maintained by the council and therefore landowners should take steps to ensure their own trees do not pose an unacceptable risk to highways users. 

Ash dieback survey image

What do I need to do? 

  • Make sure you are aware of the boundaries of your land and know what trees are your responsibility. In most cases trees in hedgerows adjoining the highway will be the adjacent landowner’s responsibility and not the council’s.
  • Identify ash trees in your ownership that are within falling distance of the carriageway or footway.
  • Look for crown dieback. This is the main symptom of the disease and is easiest to spot when ashes are in full leaf.
  • Check the base of the trunk for decay.
  • Seek advice from a tree professional if crown dieback is present. 
  • Where necessary, act to reduce the level of risk to the public. 
  • Monitor and re-inspect. One of the greatest concerns with ash dieback is the rapid decline of trees following initial infection.  

Undertaking works to diseased ash trees adjacent to the highway

Tree work carried out on or adjacent to the public highway must be carried out in accordance with the Safety at Street Works and Road Works – A Code of Practice. This is to ensure that both operatives and highways users are safeguarded. 

Ash dieback results in the timber within the tree becoming brittle, making tree felling and cutting unpredictable and more hazardous. For this reason it is important that additional safeguards are put in place, over and above what is required for other tree works, to minimise the level of risk.

Ash dieback tree works adjacent the public highway should only be carried out by suitably qualified and experienced operatives following best practice and traffic management requirements. 

Where proposed traffic management necessitates the obstruction of the highway to undertake tree works safely landowners or their contractors should notify Streetscene (Tel. 01352 701234) at the planning stage. 

Where possible the council will co-ordinate tree works on main roads to minimise traffic disruption.  

Safeguarding Wildlife 

When planning and undertaking tree works it is necessary to ensure protected species and habitats are safeguarded (e.g. nesting birds, bats and dormice), which will already be at risk because of the loss of ash tree habitat.

More information about protected species can be found on Natural Resources Wales’ website.

Protected Trees

Unless they are in severe decline works to ash trees subject to a Tree Preservation Order (TPO) will require a formal application to be submitted to the Local Planning Authority. Similarly, works to ash trees within a Conservation Area will require a formal notification.

Anyone proposing to undertake works to an ash tree on the basis it is in severe decline and deemed exempt from the requirement to obtain approval is advised to email the Council’s Forestry Officer. 

More information about protected trees can be found on the council’s other web pages.


Page 26 of the Flintshire Ash Dieback Action Plan considers the options for recovery.