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Ash Tree Disease | Chalara Dieback of Ash

by Mar 10, 2018News

This information is taken from the Forestry Commission

1. What exactly is it / Background?
Chalara dieback of ash is a disease of ash trees (Fraxinus species) caused by a fungus called Chalara fraxinea (C. fraxinea). The disease causes leaf loss and crown dieback in affected trees, and it can lead to tree death.

C. fraxinea has caused widespread damage to ash tree populations in continental Europe, especially common ash (Fraxinus excelsior), including its ‘Pendula’ ornamental variety. Fraxinus angustifolia is also susceptible. Chalara dieback of ash is particularly destructive of young ash plants, killing them within one growing season of symptoms becoming visible. Older trees can survive initial attacks, but tend to succumb eventually after several seasons of infection.

It was unknown in Great Britain until recently, but the first cases were confirmed in a nursery in Buckinghamshire early in 2012, on ash plants which had been imported from The Netherlands. Since then, more infected plants have been confirmed in nurseries in West and South Yorkshire, Surrey, Cambridgeshire and Lincolnshire, and in recent plantings of young ash trees at four sites: a car park landscaping project in Leicester, a Forestry Commission Scotland woodland near Kilmacolm, west of Glasgow, a college campus in South Yorkshire, and a property in County Durham. Our colleagues in Fera are working to trace forward to plants which had already been sold on to retail customers from the infected nursery consignments.

We are treating C. fraxinea as a ‘quarantine’ plant pathogen, which means that we may use emergency powers to contain or eradicate it when it is found. This is being done in the form of Statutory Plant Health Notices which we serve on affected owners requiring them to remove and destroy affected plants by burning or deep burial on site. Equivalent measures are being taken on land managed by the Forestry Commission. This is the only available treatment.

2. What are the symptoms?
See our Pest Alert for a description and pictures of the symptoms.Chalara dieback of ash - stem canker on young ash caused by Chalara fraxinea fungus, showing bark splitting






3. What should I do if I think my ash trees have the disease?
You should report it to one of the following Forestry Commission and Fera addresses:

4. How much of a threat is it to Britain’s ash trees?
It is potentially a very serious threat. It has caused widespread damage to ash populations in continental Europe, including estimated losses of between 60 and 90 per cent of Denmark’s ash trees. We have no reason to believe that the consequences of its entering the natural environment in Britain would be any less serious. Experience on the Continent indicates that it kills young ash trees very quickly, while older trees tend to resist it for some time until prolonged exposure causes them to succumb as well.

5. How is it spread?
Local spread may be via rain splash or even transmission by insects. Over longer distances the risk of disease spread is most likely to be through the movement of diseased ash plants. Movement of logs or unsawn wood from infected trees might also be a pathway for the disease.

6. How did it get into Britain?
The first interception of diseased ash plants found in a Buckinghamshire nursery had entered Britain in a shipment of plants for planting from a supplier in the Netherlands, who had obtained them from a nursery in Belgium. We are still investigating the pathways of the disease at the other sites.

7. What other countries have Chalara fraxinea?
According to the European Plant Protection Organization (EPPO), Austria, Belgium, the Czech Republic, Finland, France, Germany, Hungary, Italy, Lithuania, the Netherlands, Norway, Poland, Slovenia and Sweden have confirmed its presence. On the basis of symptoms, the disease has also been observed in Denmark, Estonia, Latvia and Switzerland.

8. How were diseased ash plants allowed to enter Britain? What regulatory protection measures were in place to stop it coming in?
C. fraxinea is not a “regulated” plant disease in European Union plant health law, which means that ash plants moved between Member States are not subject to inspection. EU legislation allows Member States to take national measures to prevent the entry and spread of pests and diseases not found on their territory. Our Forest Research agency has drafted a pest risk analysis (PRA), which is the first step towards assessing whether national legislation is justified in this case. This PRA is now available for public consultation and comment until 26 October 2012 on the Fera website.

9. What’s to stop more infected plants coming into Britain before we have the opportunity to adopt national legislation?
Given the known disease threat, we recommend that importers of ash trees take steps to ensure that they obtain stock from areas known to be free from the disease. Importers should seek assurances from their suppliers to this effect, and retail buyers should specify and check the origins of the plants from their suppliers. Material used for forestry purposes must be accompanied by supplier documentation to ensure traceability.

We have warmly welcomed the responsible call by the Horticultural Trade Association for its members to implement a voluntary moratorium on imports of ash trees while we consider options for the future management of the disease through the PRA consultation process.

10. What are you doing to deal with the current known introductions?
Fera inspectors have been following up plants involved with the different interceptions, requiring destruction of associated plants. A multi-agency, cross-border Outbreak Management Team has been formed, including representatives from all five countries in the British Isles. A strategy to deal with subsequent findings is being developed.

11. Will you be able to eradicate it?
It is too early to say, but we are giving ourselves the best prospects by responding promptly to findings. We need to determine the extent to which the organism is present and whether it is established, which is why we encourage all those in the trade to work with us to report any suspected findings.

12. Why has FC/Fera not acted before now?
This has been an evolving situation. The organism which was thought at one time to be causing this disease has been present since the 1800s and is already widespread, so action against it would not have been appropriate. But with better scientific techniques we now know that a different organism is responsible. The origins of this organism are not known.

13. What action can the UK take in isolation?
We can take action against findings of the disease under existing legislation, hence the precautionary response to the recent interceptions. We have drafted a pest risk analysis (see No 8 above), which will provide additional information about the risk of the organism entering, establishing and spreading in the UK and the damage it could cause. This will provide the basis for introducing specific national requirements for ash trees moving into the UK. If legislation is justified, we hope to have it in place shortly. The risk assessment has been published to provide an opportunity for anyone to comment.

14. Why is this organism not regulated at EU level?
The disease is already established in much of eastern and northern Europe, so action across the EU is not realistic. However, while the disease remains absent or under eradication from the natural environment in the UK, the UK can apply for “protected zone” status, which would introduce requirements for ash trees being moved into the UK. This could be the next step after introducing national legislation on this issue.

15. Can we not just ban imports of ash trees?
The disease has not been reported outside the EU, so banning imports from non-EU countries would not help. As regards EU movements, the risk assessment will identify the most appropriate measures and whether it is possible to introduce requirements which still allow ash trees to be traded without risk.

16. Why can’t we grow our own ash trees here instead of importing them?
We can and do grow our own trees, and people have the option to specify UK-grown trees and plants if they wish. We strongly advise tree and plant buyers to be very careful to specify healthy stock from reputable suppliers, to practise good plant hygiene and biosecurity in their own gardens and woodlands etc to prevent accidental spread of plant diseases, and to report any plant diseases. Buyers should also be aware that seed gathered from British seed is sometimes sent to nurseries in continental Europe to be cultivated before being reimported as seedlings.

17. I own or manage ash trees – how can I help?
There are several things you can do to help us get this disease under control.

a. Be vigilant – Chalara dieback could appear in ash trees anywhere in Britain, especially where young trees imported from continental Europe have been planted. Early action is essential if we are to eradicate this disease from Britain before it becomes established. We have not found any evidence of Chalara dieback in ash trees outside nurseries and recent plantings, that is, we have not found any evidence that it has spread from new plantings into longer-established woodlands and hedgerows etc in the wider natural environment, and this gives cause for hope that it is not too late.

We therefore urge you to inspect frequently any ash trees in your care, and especially any which have been planted during the past five or so years. Make yourself familiar with the symptoms of Chalara dieback from the material on our website at www.forestry.gov.uk/chalara. There are other causes of ash dieback, so it is important to distinguish them from Chalara. However, if in doubt, report it.

b. Report it – Report suspicious symptoms to us or Fera – see Question 3 for details of where to report them.

c. Buy with care – Be careful when buying plants to buy only from reputable suppliers, and specify disease-free stock. A list of countries where C. fraxinea is known to be present is at Question 7.

d. Be diligent – Practise good plant hygiene and biosecurity in your own gardens and woodlands etc to prevent accidental spread of plant diseases. See our ‘Biosecurity Guidance’ document available at http://www.forestry.gov.uk/pestsanddiseases for advice on basic hygiene and biosecurity measures which you can take.

e. Keep up to date – Check our website regularly at www.forestry.gov.uk/chalara for updates on developments. ‘Follow’ our Tree Pest News account on Twitter at www.twitter.com/treepestnews to receive rapid intelligence of new developments, delivered by text or email.

(Information about a wide range of other tree pests and diseases can be accessed via our www.forestry.gov.uk/pestsanddiseases page.)

18. I have a woodland planting grant or felling-licence agreement with the Forestry Commission to plant ash trees this season. If I do not wish to take the risk of losing the ash trees to Chalara, may I plant another species instead?
We fully understand the concerns of woodland owners who have signed up to plant ash trees in their woodland planting schemes with Forestry Commission grant support or under felling-licence conditions. We will operate a flexible approach for those customers with existing grant or licence agreements. However, where those agreements specify ash as a planting species it is essential that owners discuss the situation with their local woodland officer before planting alternatives.

19. What advice do you have for the trade?
Be careful about the sourcing of, and the specification for, your plants. (See question 7 for countries where C. fraxinea is present.) Keep good records of any imported stock, remain vigilant, inspect any recent plantings of ash, and report any suspicious signs to Fera or the Forestry Commission – see Question 3.

20. What advice do you have for the public?
At this stage, there is no evidence of the disease in the natural environment, and there are many other causes of ash dieback. Therefore, members of the public should not be alarmed if they see ash trees with dieback, because this is likely to be from other causes. However, they should report it if they have recently bought young ash plants and these start to show the symptoms illustrated in our Pest Alert. They should also follow the ‘biosecurity’ advice on any signs at affected sites, to avoid accidentally spreading the disease on their boots, clothes, bicycle wheels etc. If buying ash trees for planting, they should follow the advice in number 17c above.

21. What does a Plant Health Notice involve?
Owners of any ash plants found to be infected will be served Plant Health Notices requiring them to destroy the plants, either by burning or deep burial on site. All ash plants in a new-planting site will require to be destroyed, regardless of whether some do not have symptoms. This is because experience with other plant diseases shows that we must presume that asymptomatic plants in close proximity to symptomatic plants are almost certainly infected, but are not yet showing symptoms. However, we hope that if all parties act quickly now, few people will be affected by these measures.

22. Is there any compensation available for people who have to destroy ash plants under a Plant Health Notice?
Unfortunately we have no powers to offer compensation for plants destroyed in order to comply with a Plant Health Notice. It is felt that the available resources are best used for surveillance, research and eradication work. Plants are therefore purchased and planted at buyers’ risk, and any questions about recompense would be between the customer and supplier of the plants involved. However, we hope that few people will be put in this position if all parties move quickly now to tackle this disease.

23. Can the timber from infected ash trees still be used?
The implications for growers of ash for the timber trade would be significant if the disease were to become established in Britain. The timber in infected trees might still be usable for some purposes, although staining by the fungus might limit the range of end uses. Again, however, we hope that rapid action now by all parties will avert this scenario.

24. How many ash trees are there in Britain?
Common ash (Fraxinus excelsior) is the third most common broadleaf native tree species in Great Britain after oak and birch. Ash is the predominant tree species in approximately 129,000 hectares of woodland in Britain, and it occurs widely in much other woodland. It is a deciduous, broadleaf species native to much of continental Europe and the British Isles – a map of its distribution is available on the pest alert.

25. What is the distribution of ash trees in Britain?
See this map of ash distribution, indicating those managed by the Forestry Commission and those belonging to other owners. (Note that this map does NOT show where Chalara dieback has been found.)

26. How important are ash trees in Britain? What are their benefits?
Ash is a common component of many native woods and makes an important contribution to biodiversity and wildlife habitat. It is popular for landscaping urban facilities such as car parks. It is grown commercially for its dense, strong but elastic, easily worked hardwood, which was traditionally and commonly used for making tool handles and furniture. Usage has declined in these markets due to the advent of other materials, but the good-quality timber is still sought after for flooring and high-end, bespoke uses. It also makes excellent firewood, smoking wood and barbecue charcoal.

27. Where can I find more information?
There is further information about Chalara fraxinea on the EPPO website at www.eppo.int/QUARANTINE/Alert_List/fungi/Chalara_fraxinea.htm .