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Ash Die Back Disease - Chalara fraxinea, coming to a wood near you?

Ash trees before die back Healthy ash trees before die back

Ash die back is caused by a fungus, Chalara fraxinea (C. fraxinea). It is a serious, potentially fatal disease affecting ash trees.

The early symptoms are:

  1. Leaf loss, beginning with the leaves closest the tips of twigs and working back to larger branches and trunks;
  2. Crown dieback (progressive death of woody growths in the crown starting from the tips of branches and working back to the centre of the tree.

Ash die back has been found in a number of European countries. It was first identified in Poland in 1992 and has since been identified in Austria, Germany, Denmark, Holland, Belgium, France, Switzerland, the UK and others. It is responsible for killing approximately 9 out of every 10 ash trees in Denmark over the last 10 years and without treatment similar death tolls can be expected here and elsewhere.

According to the Forestry Commission, it was found in a consignment of infected trees:

“...sent from a nursery in the Netherlands to a nursery in Buckinghamshire in February 2012. Since then it has been found in a number of locations and situations in England and Scotland, including a car park in Leicester; a Forestry Commission Scotland woodland at Knockmountain, near Kilmacolm, west of Glasgow; a college campus in South Yorkshire; and a property in County Durham.”

In October 2012, FERA (the responsible branch of the Department of the Environment) confirmed the existence of Ash Die Back disease in East Anglia in long established ash trees (i.e. ones which don’t seem to be connected with newly planted or imported stock). The inference of this is that the disease has either “escaped” or has been carried into the UK by means other than imported stock. The most popular theory at present (and one which is consistent with the incredibly rapid spread of the disease is that it is wind borne.

How many ash trees are there in Britain?
Common ash (Fraxinus excelsior) is either the third or fourth most common broadleaf native tree species in Great Britain after oak and birch and possibly beech. It is the predominant species in about 300,000 acres of woodland in mainland Britain and it is found in some numbers in almost all mixed broadleaved woods. The population of ash is therefore thought to be about 80 million.

What are the full symptoms of Ash Die Back disease?
You can download the Forestry Commission information sheet on Ash die back disease symptoms here. And FERA has published a useful video on C. fraxinea here.

Ash Die Back Questions and Answers

What is Ash Die Back?
Ash die back is a fungal disease attacking the Common Ash in both its upright and weeping forms, plus a number of other ash species such as Fraxinus angustifolia and its varieties. It is caused by the fungus Chalara fraxinea, which was first identified in Europe in 1992.

Will affected ash trees die?
At present the answer is almost certainly. Young ash trees die almost immediately as they are defoliated in a season. Older trees may survive initially, but they are weakened by each attack and, if infected several times, they too will succumb.

Is there a cure for Ash die back?
None at present. The only treatment is to destroy affected trees by burning.

What do I do if I think my ash may be infected?
By all means send us pictures in the first instance. We should be able to diagnose almost immediately.

If it is ash die back, or if you want a second opinion, please notify one of the following. Chalara fraxinea is now regarded as a quarantine pest under national emergency measures. As such it is important that suspected instances of the disease are reported to one of the following:

  • Forest Research Tree Health Diagnostic and Advisory Service
    T: 01420 23000
  • Forestry Commission Plant Health Service
    T: 0131 314 6414
  • FERA Plant Health and Seeds Inspectorate
    T: 01904 465625


6 thoughts on “Ash Die Back Disease - Chalara fraxinea, coming to a wood near you?”

  • Vijay L. Dandiker
    Vijay L. Dandiker 29th October 2012 at 8:45 pm

    We have had this similar fungus on the pear tree of our rear garden, for more than two years, the same symptoms on the leaves & bark of our tree is similar & has led to considerable less fruit being produced and which are very hard & unsuitable to eat. Another severe cut-back has recently been implemented. This is despite a severe cut-back in 2010 of this tree to eradicate & it's subsequent regrowth and, it has affected our nearby apple tree and other trees and spoilt their fruit. Does this disease have a cross-over/transferable aspect, to other trees/plants? And, can our pear tree/plants be saved & treated, please? If so, how? Thank you

    • julian

      Interesting. One thing I ma sure of is that whatever your tree has, it is in no way related to Ash die back. The fungus that causes Ash die back is specific to Ash and does not affect pear trees which are completely unrelated. If you are able to sent pictures of the fungus you talk about from the Contact Us link on our website we may be able to advise better.

  • Sue Batstone

    There must be a reason why 10% of the ash trees in a badly infected area do not succumb. Please ask the authorities to investigate the soil fungal biodiversity of these sites, as I feel there will be a symbiotic mycorrhizae which is conferring protection to its host tree.
    Soil dwelling fungi are hugely important to plant health - your article on RootGrow is excellent.

    • julian

      Such an acute observation. Someone ought to write a book on tree breeding, biodiversity, ash die back etc.

      Your general thrust is absolutely on the money. Some ash trees, in the worst affected areas, do not succumb to the disease at all. Clearly they are genetically different in come subtle way from their less fortunate neighbours.

      Which is why calls to cut down all the ash in affected areas are, politely, ill-advised. Felling everything will certainly kill any trees that are resistant.....

      The spread of the disease also gives the lie to the notion that planting "native" trees as defined by governments across Europe including our own is a good idea. The vast majority of ash grown in this country comes from seeds collected from single species woods, planted for the purpose from genetically similar stock. Small wonder that there is no genetic diversity inside the common ash population here and elsewhere and that therefore so many should succumb at the same time. Madness.

  • Tracey Riley

    Are Rowan trees affected by the die back fungus? Three of mine died off in August I assumed it was the summer weather.

    • julian

      Rowan trees are members of the Sorbus family while Ash trees are members of the Fraxinus family. They are therefore unrelated and there has been no sign of any "cross-over" from the Fraxinus family to anything else. Generally fungal diseases tend to be plant family specific (not always true, but look likely in this case). The latin name of the disease is Chalara fraxinea which gives one the clue that it is Fraxinus specific.

      So whatever else they died of, it was not Ash die back.

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