Tuesday, 23 October 2012

Disease threat to our ash trees

There is a new threat to tree health which has appeared in Great Britain, the highly destructive Chalara dieback of ash trees, caused by the Chalara fraxinea fungus. Forestry Commission has produced a briefing note about this new threat and I repeat it below almost verbatim.


Chalara 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. The Food and Environment Research Agency (FERA) are working to trace forward plants which had already been sold on to retail customers from the infected nursery consignments.

Chalara is being treated as a ‘quarantine’ plant pathogen, which means that Forestry Commission (FC) 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 FC serves 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.

How you can help

1. 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. FC has not found any evidence of Chalara dieback in ash trees outside nurseries and recent plantings, that is, no 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.

FC therefore urges 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.

2. Report it - Report suspicious symptoms to one of the following:

Forest Research Tree Health Diagnostic and Advisory Service
T: 01420 23000;
E: ddas.ah@forestry.gsi.gov.uk

Forestry Commission Plant Health Service
T: 0131 314 6414;
E: plant.health@forestry.gsi.gov.uk

FERA Plant Health and Seeds Inspectorate
T: 01904 465625;
E: planthealth.info@fera.gsi.gov.uk.

3. 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 available in the Questions and Answers document on the website www.forestry.gov.uk/chalara.

4. 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 www.forestry.gov.uk/pestanddiseases for advice on basic hygiene and biosecurity measures you can take.

5. Keep up to date – Check the website regularly at www.forestry.gov.uk/chalara for updates on developments. ‘Follow’ the 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.)

Plant Health Notices
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.

FC is not able 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 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, hopefully few people will be put in this position if all parties move quickly now to tackle this disease.

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. However, should it get to the stage where it is infecting mature timber trees, more stringent biosecurity measures would be required to ensure that the disease is not spread further by timber movement. Again, however, hopefully rapid action now by all parties will avert this scenario.

Further information
As well as the dedicated web pages about C. fraxinea at www.forestry.gov.uk/chalara, there is further information on the EPPO website at www.eppo.int/QUARANTINE/Alert_List/fungi/Chalara_fraxinea.htm

For further help or information, please contact the woodland officer for your area (look under ‘Area’ offices in the ‘Contact Us’ area of the FC website), or contact our Plant Health Service at:

Plant Health Service
Forestry Commission
Silvan House
231 Corstorphine Road
EH12 7AT
Tel: 0131 314 6214