What you need to know – Chalara Ash dieback (Chalara fraxinea)

February 8, 2013 0 By Richard


The most important thing is to do take stock of the situation, do not rush out and fell an ash tree just because you suspect it has Chalara Ash dieback. Many tree surgeons are advantageous and ash is some of the best firewood so many tree surgeons are over keen on felling ash trees just for the firewood. Arising should be burnt onsite or sent for deep burial to avoid spreading the disease.

Things to remember

  • Ash is a ring-porous species meaning it flowers late. So do not panic if your ash tree is later than other trees to flower.
  • Chalara will not kill you tree out right and will probably survive for a long time with it. You will see some die back of the tips and you will have some deadwood in the crown. However, this weakens the tree and can allow a secondary pathogen to enter and kill the tree.
  • If you suspect you tree has Ash dieback you should first check out the symptoms section below

What Is Chalara dieback?

Trees can dieback for any number of reasons but Chalara dieback of ash trees is caused by a fungus called Chalara fraxinea (C. fraxinea). It is a serious disease which causes leaf loss, crown dieback and usually death of the tree.

Where has it come from?

Trees started dying in large numbers in Poland in 1992 from a new pathogen. It is now believed that this outbreak was due to C. fraxinea. Since then trees (in forests, urban parks and gardens and nurseries) across Europe have been dying in large numbers.

In February 2012 a consignment of trees sent from the Netherlands to a Buckinghamshire nursery was found to be infected with C. fraxinea. Over the summer other infected sites were identified, these had received nursery stock over the last 5 years. In October 2012 it was confirmed that Chalara had infected the wider environment (sites which appear to have no connection with nursery stock).

Symptoms of Chalara fraxinea

The Forestry Commission has produced two videos (below) along with a pictorial symptoms guide and a pdf guide. The Food & Environment Research Agency (Fera) has also produced this video presenting and explaining the main symptoms.

[su_youtube url=”http://www.youtube.com/watch?v=8sI7hgFZ-4g” width=”560″ height=”315″ frameborder=”0″]

[su_youtube width=”560″ height=”315″ url=”http://www.youtube.com/watch?v=U0n-9-PZySA” frameborder=”0″]

After looking at the symptoms guide you suspect you tree has Chalara you should report it to the Forestry Commission using their tree alert tool – http://www.forestry.gov.uk/website/treedisease.nsf/TreeDiseaseReportWeb which is also avalible as an app on smartphones and tablets.

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How does it spread

Here is what we know so far about the outbreak in the UK

  • It is possible the spores could be carried by the wind from mainland Europe
  • Trees need a high dose of spores to become infected
  • The spores can spread locally. Spread by logs and unsawn wood is possible but considered low risk.
  • Transportation of infected plants, which is now restricted by the government.

Charla Upadated Map - 19 Dec 2012 View larger map

What is the government doing

C. fraxinea is being treated as a quarantine pest under national emergency measures, and it is important that suspected cases of the disease are reported. The Forestry Commission are operating a ‘trace forward’ operation to locate sites supplied by affected nurseries.

What should i do?

After checking the symptoms you should report all suspected cases to the Forestry Commission. The commission state that you do not need to do anything unless they serve you with a notice. You should monitor the tree as the disease progresses and prune/fell any trees which threaten to fall and cause any injury or damage. Infact you should do this to all of your trees (a recently dead and structurally sound tree is a lot cheaper and easier to deal with than a rotten precarious one).

If you think you have spotted the disease, please check the Forestry Commission’s symptoms video and symptoms guide , and our guide to recognising ash trees, before using their Tree Alert form.

Where can i find out more?