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More pictures and spore release video

chalara-electron The Chalara fraxinea pathogen
(credit: Susanne Mottinger-Kroupa)

Further to our earlier post on ash dieback disease, we can now provide more images and information from the University of Vienna on the symptoms of the Chalara fraxinea infection of ash trees.

In addition, again from University of Vienna, we have a video of the release of fungal spores from ash twigs infected with the reproductive stage of C. fraxinea, called Hymenoscyphus pseudoalbidus. It is this trumpet-shaped mushroom stage that we may see develop in the UK in spring 2013, and it is the prevention (or at least limitation) of this stage that needs to remain in sharp focus.

The ash tree dieback story continues, and we have been fortunate to talk with tree experts at the IFFF to understand their views on what the future might hold for the UK's ash tree population.

The prognosis isn't pretty, but then you will have gathered that already from media coverage of ash tree dieback. There are, however, glimmers of hope – and luckily, such glimmers are very much grounded in what has already been seen in other countries. Some ash trees can be naturally resistant to the disease, even of the same species and variety that are succumbing to the infection, as the image below shows:

The UK's task in the coming months and years is twofold: first, to do all we can to sensibly limit the spread of the disease (sensibly being the operative word – a mad rush to deforest ash could remove genetically resistant trees); and second, to ensure that we understand and manage the ongoing genetic diversity of the surviving trees.

On page 2 of this post, we have more images of ash trees that have been infected with the C. fraxinea fungus, which can help you to confirm whether your ash trees are suffering from dieback.

Ash tree dieback disease images

(For more images, please see our earlier blog post on ash dieback disease)

This section presents a gallery of the Chalara fraxinea fungus and trees infected by it. Images include microscopic images of the pathogen, lab-grown fungal cultures, branch and stem lesions, leaf wilt, and crown dieback.

Click the pictures to view full size...


Fig 1: The pathogen Chalara fraxinea under a microscope

chalara-fraxinea-microscope (credit: Katharina Kräutler)
chalara-fraxinea-microscope-2 (credit: Erhard Halmschlager)


Fig 2: Diseased leaves, twigs and branches eventually fall to the floor, setting the scene for the reproductive stage of the fungus – a trumpet-shaped mushroom called Hymenoscyphus Pseudoalbidus

hymenoscyphus-pseudoalbidus-2 Reproductive stage of ash tree dieback
(credit: Thomas Kirisits)
hymenoscyphus-pseudoalbidus-3 Small white trumpet-shaped mushrooms release Chalara fraxinea spores into the air
(credit: Thomas Kirisits)


Fig 3: Cultures of the Chalara fraxinea fungus, grown for research purposes at the IFFF in Vienna.

hymenoscyphus-pseudoalbidus-cultures-1 Research into ash dieback fungus cultures
(credits: Susanne Mottinger-Kroupa, Thomas Kirisits)
hymenoscyphus-pseudoalbidus-cultures-2 Cultures of Chalara fraxinea
(credit: Thomas Kirisits)

Fig 4: A tell-tale sign of ash dieback disease is a necrotic lesion (tissue death) on stems, twigs and branches

ash-lesion-1 (credit: Thomas Kirisits)
ash-lesion-2 (credit: Thomas Kirisits)
ash-lesion-3 (credit: Thomas Kirisits)

Fig 5: 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.

ash-dieback-leaf-loss (credit: Thomas Kirisits)
ash-dieback-leaf-wilt (credit: Thomas Kirisits)
ash-dieback-leaf-loss-2 (credit: Thomas Kirisits)
ash-dieback-leaf-wilt-2 (credit: Thomas Kirisits)


Fig 6: Continued leaf loss works back towards the trunk of the ash tree, giving the disease its common name of Ash Tree Dieback.

ash-dieback-young-tree Young tree with ash dieback disease
(credit: Thomas Kirisits)
ash-dieback-diseased-trees Ash trees damaged by chalara
(credits: Josef Wampl, Thomas Kirisits)
ash-branch-dieback Ash die back damage
(credit: Thomas Kirisits)
ash-advanced-dieback Severely diseased ash tree
(credit: Thomas Kirisits)



ash-dieback-shoot-twig-branch Row of damaged ash trees
(credit: Thomas Kirisits)

Fig 7: Cross-sections of dead wood show how far into the trunk necrotic lesions can reach

ash-dieback-in-roots (credit: Thomas Kirisits)
ash-dieback-dead-shoot-impact-on-trunk (credit: Katharina Kräutler)
ash-dieback-wood-discoloration (credits: Erhard Halmschlager, Thomas Kirisits)


The fungus in the UK would reach its reproductive (sexual) stage around spring 2013. Official advice is not to disturb ash leaves and debris. We think that it may be better to rake them up in winter and burn them before the spores are released as temperatures rise.

We would very much welcome your thoughts and comments on ash dieback disease – please feel free to leave them below.

  • profile_image
    Sheryll Jerred | 2023-07-12 05:49:34
    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?
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    Darren | 2023-07-12 05:49:34
    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!
  • profile_image
    Dan Stevens | 2023-07-12 05:49:34
    A lot of really good info here thanks guys, a credit to the gardening community!
  • profile_image
    olsson | 2023-07-12 05:49:40
    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.
    Mark Cadbury | 2023-07-12 05:49:40
    I think that the government website on this matter is the most definitive place to look (, or the Woodland Trust ( or the RHS website (
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