Ash Dieback Branch Tips Adobe Stock 273572539

What is Ash Dieback?

Posted onJuly 02, 2019

Here at Teign Trees & Landscapes we are shocked by the ongoing devastation caused by the fungul disease Ash Dieback or Chalara.

The latest information from that Ash Dieback has now taken hold across much of the UK, including Devon. The disease is likely to have a major impact on Devon’s countryside, much of which is patterned by a rich network of hedges, hedgerow trees, small copses and woodland. If the Ash trees go, and evidence suggests we will lose over 90% of them, then the character of our landscapes is likely to change dramatically, with loss of trees, hedgerows and the wildlife they support.

A highly infectious fungal disease known as ‘Ash dieback’ (previously also referred to as Chalara) is threatening to wipe out our native ash (Fraxinus excelsior), as well as most other non-native members of the ash family. Ash trees are valuable features of Devon’s landscape and are present in our native woodlands and hedgerows. Ash is one of our three main hedgerow trees, along with oak and beech, and makes up about one sixth (16%) of their shrubby growth. Both native and ornamental ash trees are present in parks and gardens.

In 2013, Defra published its Chalara Management Plan; since then Devon County Council has been fully supporting its objectives.

Despite this, the airbourne spread of the disease has continued, and its impacts on Ash trees in our towns and countryside are now becoming noticeable.

What you can do

  • Manage risks. Check Ash trees in land under your control for signs of the disease. See information on how to recognise signs of the disease in Ash trees. Don’t wait until the disease makes a mature tree unsafe. If you are a landowner, you are responsible for managing the health and safety risks from dead and dying trees on your land. Monitor trees near highways and rights of way or areas with high levels of public access for signs of the disease, and if risk assessments show these as a hazard, plan careful pruning or felling by an ARB Approved Contractor, such as us here at Teign Trees & Landscapes SW Ltd. Make sure that any work to trees also manages risk of harm to wildlife- particularly legally protected species – see Guidance. Contact Devon County Council Highways if work to trees could impact on a highway. Trees in open countryside away from publicly accessible areas pose the least risk, and if the disease takes hold there are benefits of allowing nature to take its course if safe to do so. A tree that proves genetically resilient to the disease has yet to be found, but such a tree could be out there.

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.


  • Dark lesions – often long, thin and diamond-shaped – appear on the trunk at the base of dead side shoots
  • The tips of shoots become black and shrivelled
  • Blackened, dead leaves – may look a bit like frost damage
  • The veins and stalks of leaves, normally pale in colour, turn brown
  • Saplings have dead tops and side shoots
  • In mature trees, dieback of twigs and branches in the crown, often with bushy growth further down the branches where new shoots have been produced
  • In late summer and early autumn (July to October), small white fruiting bodies can be found on blackened leaf stalks.


  • The disease is spread by spores from the fruiting bodies of the fungus produced on fallen ash leaves. These airborne spores can disperse naturally via wind over tens of kilometres
  • Prior to the ban in October 2012 on the movement of Ash trees, spread over longer distances was likely to have been via the movement of infected Ash plants.
  • We don’t know what the full impact of ash dieback will be. Evidence suggests young trees are killed quickly while many mature Ash trees can resist infection for some time until eventually dying or becoming weakened and succumbing to attack from another pest or pathogen.
  • Scientists have developed techniques to identify individual trees that are less susceptible to ash dieback disease, this technique combined with resistance breeding trials, can be used to grow trees that are more likely to survive the disease.

For more information on Ash dieback symptoms and causes, check out ourTree Services page.

Who to Contact if you believe you have identified Ash Dieback:

Food and Environment Research Agency on 01904 465625

or the Forestry Commission on 0131 314 6414.

For more information and pictures of Ash Dieback check out

If you have any questions, concerns or require an Arboriculture Association Approved Tree Surgeon to check your trees, please contact us here at Teign Trees & Landscapes SW LTD.

Photo Credit Matthew J. Thomas | Adobe Stock