Defra

Why the concern?

Phytophthora ramorum is an exotic fungus-like plant pathogen which causes damage to trees, shrubs and other plants.  Since the mid 1990’s, it has caused widespread death of millions of trees in forest environments in coastal California and Oregon in the USA.  Because the most commonly affected trees that have been killed are tanoaks (not true oaks) as well as several true oak species, this extensive phenomenon is commonly known as ‘Sudden Oak Death’ in the USA.  The pathogen was first found in the nursery trade in the USA/Canada in 2001.

In Europe, including the UK, P. ramorum has been found mainly on container-grown Rhododendron, Viburnum and Camellia plants in nurseries.  It was first detected in the UK in 2002.

By the end of January 2008 P. ramorum had been identified 793 times at 686 different sites in England and Wales.  At some sites there have been repeated outbreaks.  At 529 of the outbreaks, the site has been found clear following eradication action.  Controls are still in place at 264 sites.  (Click here for latest findings.)

Between October 2003 and December 2007, 27 trees have become affected with bleeding cankers in GB and at least another 14 trees with these symptoms over the same time period in the Netherlands.  In Britain, one of the affected trees (the first) was in the south-east of England, with most of the remainder in the south-west of England.  Recently (October 2007) a beech tree has been found with a bleeding canker in a historic garden in West Yorkshire, and around the same time a red oak was diagnosed with the disease in Northern Ireland.  All the diseased trees have been close to large numbers of infected rhododendron.

A P. ramorum information leaflet and poster (pdf) are available which provide guidance and advice on the symptoms and spread of the disease.

What is being done?

Following the first  finding of Phytophthora ramorum on viburnum at a nursery in Sussex in February 2002, emergency measures were introduced in Great Britain.  The initial measures included destruction of infected plants, a ban on imports of susceptible material from affected areas of the USA,  and notification of movements of susceptible nursery stock i.e. rhododendron (other than R. simsii), and viburnum. 

These measures were notified to the EU Standing Committee on Plant Health, which agreed EU-wide emergency measures in November 2002, based largely on GB’s action.  Those measures are still in place.

The relevant EU legislation can be found at:
http://eur-lex.europa.eu/LexUriServ/site/en/oj/2002/l_252/l_25220020920en00370039.pdf

http://eur-lex.europa.eu/LexUriServ/site/en/oj/2004/l_154/l_15420040430en00010007.pdf

http://eur-lex.europa.eu/LexUriServ/site/en/oj/2007/l_090/l_09020070330en00830085.pdf

Legislation in England relating to P. ramorum can be found at:
http://www.opsi.gov.uk/si/si2007/uksi_20072155_en_1.htm
         
http://www.opsi.gov.uk/si/si2004/20042590.htm

A comprehensive programme of research has been in place since 2002 to support the current eradication and containment action and to help better assess the risk from this pathogen.

What measures are being taken against the disease?

Since the identification of P. ramorum an annual survey of all premises which trade in susceptible plants has been undertaken.  Wholesale nurseries have been subject to a minimum of two visits per year.  An initial comprehensive survey of parks, gardens and woodlands has been followed by an annual targeted survey of approximately 900 sites.  For any site, whether trade, park, garden or woodland, where infection has been identified, additional visits and appropriate measures have been undertaken to contain and eradicate the disease. (Click here for information on ongoing research and development projects and activities.)

There is no fungicidal treatment which will reliably kill established infections on plants.  Some treatments may help to protect plants from infection, or reduce symptoms.  This may be helpful in slowing disease development and spread, but may also mask infection, making it more difficult to determine whether a nursery is, in fact, pathogen-free.  It is for this reason that there is currently a ban on applying fungicides to plants which are under official hold in nurseries where infection has been found.

The main means of control, both on nurseries and in gardens and woodland sites, has been destruction of infected plants. (Click here for information on the eradication and containment action required against all findings.)

On nurseries, susceptible plants within 2m are destroyed and susceptible plants of the same lot or within 10m of the finding are held for 3 months of active growth and inspected at least twice before release.  The level of findings on GB nursery stock moving in trade has fallen since the introduction of the EU measures (from 3% in 2004 to 1% in 2007).

At a selected number of woodland gardens and areas of semi-managed or unmanaged woodland, clearance of all R. ponticum, whether infected or not, has proved effective at reducing inoculum levels and appears to have prevented further infection of trees on those sites.  So far almost all of the trees which have been found to have bleeding cankers in GB have either been in direct contact with heavily infected R. ponticum or, within a few metres of it.

Import controls have been introduced on all susceptible plants from the USA.  Within the EU, rhododendrons (other than R. simsii), viburnums and (since 2004) camellias can only be moved from nurseries which have been officially inspected and found free from the disease, or where appropriate eradication measures have been taken.  Consignments of these plants must be accompanied by plant passports (used already in the EU to manage risks from a number of other plant pests and diseases).  This aims to ensure that plants moved in trade are free of the pathogen; if symptoms develop after movement, the infection can be traced back to the originating nursery and follow-up inspections carried out at sites which have received plants from the same batch.