Phytophthora ramorum
is the fungal-like pathogen which is the causal agent of a condition known in the USA as Sudden Oak Death. The pathogen was first found in the UK in a garden centre in April 2002 and has since been found mainly on viburnums and rhododendron in a significant number of nurseries and garden centres surveyed by Defra Plant Health & Seeds Inspectorate (PHSI) in England and Wales and by the Scottish Government Rural Payments and Inspections Directorate (SGRPID - formerly SEERAD) in Scotland. In November 2003, the first case of an established tree affected by disease was confirmed and an announcement on these finds was made in November 2003 by Ben Bradshaw, then Defra's Minister for the Environment, Food and Rural Affairs. As the source of the tree infection, appeared to be diseased rhododendrons, the Forestry Commission undertook a major survey of Britain’s woodlands where trees were in mixture with Rhododendron ponticum. The survey was carried out between January and March 2004 and did not find any cases of P. ramorum. The announcement of the results of this survey was made on May 10 2004, and the news release is included in these pages. A second survey, on a reduced scale in England and Wales, was undertaken between May and August 2004 but it also did not find any cases of P. ramorum.
In the autumn of 2004, a new Phytophthora, now formally named P. kernoviae, was discovered during the inspection of two on-going outbreaks of P. ramorum, one in Cornwall and one in South Wales. Information on P. kernoviae can be found here.
In 2005, the Phytophthora Programme Board decided that, in the light of these continuing outbreaks, it was necessary to revisit all those high-risk sites, which were surveyed in 2004, over a 5 year period, with 20% of the total being surveyed annually. This would determine whether they were still free of symptomatic plants. This re-survey commenced in 2005 and is programmed to continue until 2009. In addition surveys to determine if both P. ramorum and P. kernoviae were widespread in Cornwall and other parts of England and Wales were carried out in 2005 and 2006. To view all of these survey reports. Between 2004 and 2007, woods in Cornwall which had been identified as having infected Rhododendron ponticum were inspected to ascertain if the trees were also infected. This Intensive Tree Survey, to assess the Incidence of Phytophthora ramorum and Phytophthora kernoviae In Woodland Trees in Cornwall is likely to continue in 2008. In Scotland since 2003 SG-RPID has conducted annual surveys during which specialist gardens, parks, estates and urban landscaped areas have been examined for both P. ramorum and P. kernoviae. In September 2007 the first outbreak of P. ramorum in an established garden in Scotland was confirmed. Since then there have been a further nine outbreaks of P. ramorum and two of P. kernoviae all in garden sites. Further information can be found on Scotland Government website. In August 2007 the first finding in Northern Ireland of P. ramorum on an established plant was confirmed in a domestic garden. Subsequently there have been a further five findings involving established plants. The disease has also been found in the Channel Islands The current list of plants susceptible to P. ramorum in the USA include: Acer macrophyllum, Aesculus californica, Arbutus menziesii, Lithocarpus, Quercus spp, Rhamnus californica, Rhododendron spp, other than R. simsii (pot azaleas – otherwise known as Azalea indica), Umbellularia californica, Vaccinium ovatum, and Viburnum spp. Although P. ramorum is most damaging in the USA, it also occurs in Europe but there are significant differences between the North American and European populations of the pathogen. In Europe P. ramorum was first recorded in 1993 both in Germany and the Netherlands but was confined to rhododendron and viburnum. It has since been found in Belgium, Finland, Denmark, France, Ireland, Italy, Norway, Poland, Spain, Switzerland, and Sweden. One isolated outbreak in the Czech Republic has been eradicated. The first finding in the UK on Viburnum was recorded in April 2002. Rhododendron and Viburnum are still the main hosts, but it has since been found on many plant species including Camellia, Hamamelis, Leucothoe, Pieris, Kalmia, Syringa, Lilac, Vaccinium vitis-idaea, Drymis winterii, Magnolia and in 2003 on ten potted Taxus baccata (yew) trees in a Lancashire nursery. A full list of hosts and findings in Europe is given at http://rapra.csl.gov.uk (For a complete list of the species affected by P. ramorum which has been compiled from European and North American records by CSL. Further information on findings in nurseries throughout the UK and the legislative measures is on the Defra website Susceptibility of Trees in Europe Except where disease levels are intense on carrier hosts such as R. ponticum, P. ramorum is unlikely to infect European species of oak (such as common or pendunculate oak (Q. robur) or sessile oak (Q. petraea), Laboratory tests on their relative susceptibility indicates that these species are more resistant than their American cousins. Some conifer species such as Sitka spruce (Picea sitchensis) may also be susceptible. Up until November 2003, the disease had not been found in any established trees anywhere in Europe although some young yew trees (Taxus baccata) growing in pots in a nursery, were found to be infected. They had been growing next to infected viburnum plants and shared a common irrigation system.
In November 2003, the first P. ramorum infected tree outside the USA was confirmed on a mature specimen of southern red oak (Quercus falcata) in Sussex. Since then, the Dutch have confirmed P. ramorum infections on several beech (Fagus sylvatica) and red oak (Quercus rubra) trees. Up to early December 2006 a range of tree species in Cornwall including beech, southern beech (Nothofagus obliqua) horse chestnut (Aesculus hippocastanum), sweet chestnut (Castanea sativai), sessile oak (Quercus petraea), Turkey oak (Q. cerris) and sycamore (Acer psuedoplatanus) have been found with potentially lethal infections. In addition, other tree species have been found suffering from leaf and shoot infections caused by P. ramorum. These include holm oak (Quercus ilex), Turkey oak, ash (Fraxinus excelsior), sweet chestnut, Magnolia , Michelia and Eucalyptus species. Oak decline In the UK, and elsewhere across Europe, there is already oak mortality and dieback of oak from a complex cause known as ‘oak decline’. This is fairly widespread; although individual pockets can be localised and intense. In some cases the decline is associated with infection by other Phytophthoras, but these are mainly root infecting species whereas P. ramorum causes stem cankers. Oak decline also involves recurrent episodes of drought, other root infecting fungi, repeated insect defoliation and scale insect attack.(see Forestry Commission Information Note 22).
Exotic Pest Alert
We have already distributed an Exotic Pest Alert to specialists in the field. This gives further information as well as photographs of the disease and its symptoms on oaks in California. To order copies of the Alert. Pest Risk Analysis Pest risk analysis for both P. ramorum and P. kernoviae are available on the Defra website.
A full list of hosts and findings in Europe and the USA is given at http://rapra.csl.gov.uk Who Does What? Defra’s Plant Health Division (PHD) has overall policy and legislative responsibility for P. ramorum relating to plants and plant produce in England and also co-ordinates UK plant health policy; liaison with direct stakeholders and interested parties at national level and for co-ordination of action across Defra. The Plant Health and Seeds Inspectorate (PHSI) is responsible for enforcing all aspects of the policy; carrying out inspections, surveys, eradication campaigns and liaison with local Government and stakeholders. The Central Science Laboratory (CSL) provides scientific and technical advice/support to PHD/PHSI and carries out all diagnostic services. The Forestry Commission’s Plant Health Service (PHS) has overall policy and legislative responsibility for all aspects of P. ramorum relating to forest trees and wood. Forest Research (an agency of the Forestry Commission) is responsible for research, scientific advice and diagnosis of P. ramorum on trees. Its Technical Support Unit carries out woodland surveys. The Scottish Government Rural Directorate - Agricultural Commodities Branch is responsible for policy and legislative matters for P. ramorum relating to non-forestry plants material in Scotland, including liaison with Scottish stakeholders. The Scottish Government Rural Payments & Inspections Directorate (SG-RPID) is responsible for enforcing policy through inspections, surveys, eradication campaigns and liaison with Scottish local authorities. SASA (Science and Advice for Scottish Agriculture) provides scientific and technical support to the Scottish Government, along with diagnostic services. The Welsh Assembly Government’s Plant Health and Biotechnology Unit has policy and legislative responsibility for plant health and P. kernoviae relating to non-forestry plant material in Wales. Under an agreement with Defra, all enforcement and inspection activities are carried out on its behalf by Defra’s PHSI. (Last updated May 2008)
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