Wild rhododendron is one of the main hosts for Phytophthora ramorum [sudden oak death] its rampant in Cornwall and slowly spreading through Devon and rest of the country.Been taking out all rhodos in the woods I maintain in a bid to keep it out ,its not only oaks that are affected its a major threat to our countryside as we know it.
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hytophthora ramorum
Phytophthora ramorum is the fungal-like pathogen which is the causal agent of a condition Pknown 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. These have been in a significant number of nurseries and garden centres surveyed by Defra Plant Health & Seeds Inspectorate (PHSI) in England and Wales (now part of Fera – the Food and Environment Research Agency) and by the Scottish Government Rural Payments and Inspections Directorate (SGRPID) 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.
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 outbreaks of P. ramorum and P. kernoviae mainly 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: Abies spp, Acer macrophyllum, Aesculus californica, Arbutus menziesii, Lithocarpus densiflorus, Pseudotsuga menziesii Quercus spp, Rhamnus californica, Rhododendron spp, Sequoia sempervirens, 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 late 2009 an outbreak of Phytophthora ramorum was discovered on Japanese Larch trees in Devon, Cornwall and Somerset. This was the first time that stem lesions caused by P. ramorum had been found on conifer species. Many of the infected trees are not growing in proximity to rhododendron (known to be a host of P. ramorum) which raises the question of how they have become infected. Symptoms have also been found on Western Hemlock and a selection of broadleaf species (beech, birch, and some oaks) growing in the same area.
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 many other European countries, but mainly affecting ornamental nursery plants. 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 other ornamental plant species including Camellia, Hamamelis, Leucothoe, Pieris, Kalmia, Syringa, Lilac, Vaccinium vitis-idaea, Drimys winterii and Magnolia.
A full list of hosts and findings in Europe is given at
rapra.csl.gov.ukA complete list of the species affected by P. ramorum has been compiled from European and North American records by Fera. Further information on findings in nurseries throughout the UK and the legislative measures is on the Defra website
Symptoms Caused by P. ramorum
In Europe P. ramorum has most frequently been found infecting the leaves and shoots of ornamental shrubs such as rhododendron, viburnum, pieris and camellia. Although it does not usually kill these plants, infected leaves of some of these ‘foliar hosts’ can generate many spores and in sufficient numbers these spores can then infect the bark of certain tree species.
Typical symptoms on rhododendron include leaf-blackening, wilted shoots and die-back. On individual leaves, blackening of the leaf stalk usually extends into the leaf along the mid-vein, although blackening at the leaf tip can also occur. Disease progress can be so rapid that shoots wilt and the leaves hang down.
On trees, symptoms are lesions – sometimes known as bleeding cankers. Fluid is exuded from infected bark, visible as a black exudate that can dry to a crust on the trunk. The inner bark under this bleeding area is usually discoloured and dying. Trees die when the lesions become extensive on the main trunk.
Susceptibility of Trees in Europe
Except where disease levels are intense on foliar 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.
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 (f*gus sylvatica) and red oak (Quercus rubra) trees. Up to early December 2008 most infected trees with bleeding lesions have been found in Cornwall, with beech the most frequently affected species. Other tree species found with potentially lethal infections caused by P. ramorum have been rare but include southern beech (Nothof*gus obliqua) horse chestnut (Aesculus hippocastanum), sweet chestnut (Castanea sativai), sessile oak (Quercus petraea), Turkey oak (Q. cerris) and sycamore (Acer psuedoplatanus).
In addition, a few 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.
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