Ash Tree Dieback Disease

Ash saplings infected by the Chalara fraxinea fungus were found at Buckingham Nurseries at the beginning of 2012

Say hello to the Ash dieback fungus formerly known as Chalara fraxinea or Hymenoscyphus pseudoalbidus: Hymenoscyphus fraxineus.

The general picture twelve years on is that this rollicking, single-minded plague creeps inexorably through air, soil, and aboard insects, piercing our beloved Common Ash both leaf and stem. Many will not survive the embrace.

Of all the trees, that grew so fair…

But here’s the good news: Chalara / Hymenoscyphus (which only affects Common Ash, Fraxinus excelsior, not any other tree, including Mountain Ash, which is the unrelated Sorbus aucuparia) is a pillager, not a methodical assassin.
It rampages through Ash tree populations, killing some, maiming others, and occasionally missing its mark entirely. Some mature trees only experience partial die back, and then recover in other places, and a few trees seem more or less resistant.
Trees in woodland seem more susceptible, while trees out by themselves in the open, or in urban areas with no bare soil around and fungicidal, dry, polluted air seem to be much less affected.

So, while Ash is going to decline (and cost a lot of money tidying up in the process), it isn’t going extinct just yet, and should be much less affected than Elms were by Dutch Elm Disease.

Management of Ash Die Back is in full swing, you’ll find everything you need here on the Gov website, with specific advice for people who just own one or a few ash trees, and for people managing Ash woodland.

From the University of Vienna, we have a 240p potato-quality video of the release of fungal spores from ash twigs infected with the reproductive stage, which was originally named Chalara fraxinea, since updated to Hymenoscyphus fraxineus.

It was filmed in 2012, so that’s why it looks like it was filmed in 2006.

Back in 2012, we were fortunate to talk with tree experts at the Institute of Forest Entomology, Forest Pathology and Forest Protection, IFFF. They shared the images below with us, and we spoke about doing what we can to sensibly limit the spread of the disease. A mad rush to deforest Ash could remove genetically resistant trees, and interbreeding those trees is the key to resistant Ash populations in the future.
If all goes well, it could be possibly to re-introduce highly resistant Ash trees in the future.

Ash tree dieback disease images

Images include microscopic images of the pathogen, lab-grown fungal cultures, branch and stem lesions, leaf wilt, and crown dieback.

The fungal pathogen Chalara fraxinea under a microscope
The fungal pathogen under a microscope (credit: Katharina Kräutler)
The fungal pathogen Chalara fraxinea under a microscope close up
(credit: Erhard Halmschlager)

Diseased leaves, twigs and branches eventually fall to the floor, setting the scene for the reproductive stage of the fungus – a trumpet-shaped mushroom

White Hymenoscyphus fraxineus mushrooms on Ash twigs
Reproductive stage of ash tree dieback
(credit: Thomas Kirisits)
White Hymenoscyphus fraxineus mushrooms on Ash twigs
Small white trumpet-shaped mushrooms release spores into the air
(credit: Thomas Kirisits)

Cultures of the fungus, grown for research purposes at the IFFF in Vienna.

Research cultures of the Chalara fraxinea fungus
(credits: Susanne Mottinger-Kroupa, Thomas Kirisits)
Research cultures of the Chalara fraxinea fungus
(credit: Thomas Kirisits)

How to Identify Ash Die Back Disease

A tell-tale sign of ash dieback disease is a necrotic lesion (tissue death) on stems, twigs and branches:

Identify Ash Die Back Disease on new bark, a brown stain on the green new bark
(credit: Thomas Kirisits)
Identify Ash Die Back Disease on new bark, a brown stain on the green new bark
(credit: Thomas Kirisits)
Identify Ash Die Back Disease on new bark, a brown stain on the green new bark
(credit: Thomas Kirisits)

Once the fungal infection spreads fully across a stem or branch, nutrition is cut off beyond that point and leaves begin to wilt and die.

Wilting dying Ash leaves
(credit: Thomas Kirisits)
Wilting dying Ash leaves
(credit: Thomas Kirisits)
Dry dead Ash leaves at the end of the leaf stem with living leaves at the base
(credit: Thomas Kirisits)
Dead dry Ash leaves in the canopy, similar to Autumn but during the summer.
(credit: Thomas Kirisits)

Continued leaf loss works its way back towards the trunk of the ash tree:

Young tree with ash dieback disease
(credit: Thomas Kirisits)
Three trees of different ages all with ash dieback disease causing bare upper canopies
Ash trees damaged by chalara
(credits: Josef Wampl, Thomas Kirisits)
Ash die back damage on a large Ash tree. Canopy is bare, with weaker regrowth trying to take its place
(credit: Thomas Kirisits)
Big old Ash tree with very sparse canopy, only a little regrowth.
Severely diseased ash tree
(credit: Thomas Kirisits)
Row of damaged ash trees, showing how some are almost dead but others are only a little affected.
Row of damaged ash trees
(credit: Thomas Kirisits)

Cross-sections of dead wood show how far into the trunk necrotic lesions can reach

Cross-sections of dead wood show how far into the trunk necrotic lesions reach
(credit: Thomas Kirisits)
(credit: Katharina Kräutler)
(credits: Erhard Halmschlager, Thomas Kirisits)

Has ash dieback disease come to your area? Comments below…

Image credits: By kind permission of Thomas Kirisits, Josef Wampl, Christian Freinschlag, Katharina Kräutler and Michaela Matlakova of the Institute of Forest Entomology, Forest Pathology and Forest Protection (IFFF), Department of Forest and Soil Sciences, University of Natural Resources and Life Sciences, Vienna (BOKU), Vienna, Austria

By Ashridge Support

Ashridge Nurseries has been in the business of delivering plants since 1949.


  1. Sheryll Jerred says:

    Should we avoid putting leaves in compost bins?
    Are spores likely to spread to other plants should the compost then be used on the garden?

  2. Darren says:

    Hi Sheryll,

    If you have ash trees in your garden, and you’re not sure whether they’re healthy, the safest route will always be to dispose of all leaf and twig litter by burning.

    The fungus itself can be carried around by touch (on boots, wheelbarrows, tools, pets, etc), so in theory it can be ‘on’ the leaves and twigs of other trees (what scientists call a ‘vector’ for the infection). But it won’t infect those other trees – it’s important to remember that this fungus will only infect ash trees.

    If you don’t have ash trees in or near your garden, you shouldn’t worry – compost away!

  3. Dan Stevens says:

    A lot of really good info here thanks guys, a credit to the gardening community!

  4. olsson says:

    This has been helpful. We live near a wooded area in Lanc’s and have 2 large ash in the garden. The smallest one is obviously infected. Both trees are about 50 plus years old. I am happy to leave them alone apart from some pruning. They are an important part of the hedge row which is mostly hawthorn and is the boundary to the property.
    More advice would be helpful.

  5. Charlotte says:

    My mountain ash (rowan) died of a honey fungus infection this year. Ash are resistant to honey fungus, rowan are resistant to ash dieback. It doesn’t really matter to the tree which fungus kills it.

    1. Ashridge Nurseries says:

      A dead tree is a dead tree, I agree, but the fungi are quite different.

      Honey fungus attacks through a “root system” that travels relatively slowly but kills fast. It is not species specific, and very few tree species are truly resistant.
      It is potentially preventable: planting susceptible trees inside an impermeable barrier in the top 6″ of soil should keep them safe. It also tends to attack weaker and more stressed subjects, so the best prevention is healthy soil with loads of mulch to produce healthy plants.

      Ash die back, however, is spread by the wind and so travels fast. It is specific to the Fraxinus family only, and attacks them all, regardless of the tree’s health. It is neither preventable nor treatable, but unlike Honey Fungus – which is a guaranteed death sentence, eventually – it seems that some Ash trees have a degree of resistance.

Leave a comment

Your email address will not be published. Required fields are marked *

Back to top