Forestry Commission - News - native oaks susceptible to new tree disease

Two cases of a new pathogen that could seriously affect trees have been found in native English oak (Quercus robur) trees in a wood near Redruth in Cornwall. This is the first discovery of fungal disease caused by this Phytophthora species in native oak trees in Britain.

The new pathogen was first discovered in the wood in Cornwall earlier this year when it was found on rhododendron plants and a beech tree. The phytophthora, known informally as Phytophthora taxon C, is so new it does not yet have a formal scientific name but the tree pathologist who first discovered it, Clive Brasier, Professor Emeritus at the Forestry Commission’s Forest Research agency, has dubbed it Phytophthora kernovii – the ancient name for Cornwall. Professor Brasier, and colleagues at the Commission’s Surrey-based research centre, are monitoring two more oak trees in the area which they suspect may also be infected.

The pathogen, is related to Phytophthora ramorum, known in the USA as Sudden Oak Death because of the widespread blight it has caused on American oak species. However, until now, native British oaks have proved to be resistant to both pathogens. Since the first discovery of P. ramorum in Britain early in 2002, neither laboratory tests nor painstaking surveys of more than 1500 woodland and forest sites across Britain have established any susceptibility of native oak trees to the deadly fungus.

Although P. ramorum is known to exist in more than a dozen countries throughout Europe, the new Phytophthora is so far thought to be specific to Britain. A major concern is that laboratory tests and observations in the wild indicate that it is more aggressive, and much faster spreading, than P. ramorum. Rhododendron, the main host and source of infection, succumbs in just a few weeks, rather than months.

This latest discovery raises fears over the pathogen’s potential impact on Britain’s 200 million oak trees, as well as other native tree species that may now prove to be susceptible.

The Forestry Commission’s Head of Plant Health, Roddie Burgess, said:

“Our hope was that

P. ramorum

, and this more virulent pathogen, would not spread to native species. This new evidence indicates that this is not the case. We need to ensure that the precautions we take to identify and control the spread of this disease are commensurate with this significantly more serious threat.

“The infected trees are already within an area quarantined because of the presence of

P. ramorum

. Any infected plants are being destroyed, as are any potential hosts in the immediate area.”

In the biggest exercise of its type ever undertaken in Britain, Defra and other Government plant health inspectors have more than doubled their visits to nurseries and garden centres and inspected more than 1000 lorries carrying imported plants from the continent. The Forestry Commission has surveyed almost 1500 woodland sites. P. ramorum has been found at more than 370 sites in England and Wales, mostly on shrubs at nurseries and garden centres. At most of these sites the disease appears to have been successfully eradicated. There have been a few finds on trees, largely restricted to large gardens in the south of England.

If anyone suspects the presence of the disease on plants they should contact their local Defra or SEERAD office. If the disease is suspected on trees the contact should be the Forestry Commission. Further information on the two phytophthora is available on the Forestry Commission and Defra websites – /www.forestry.gov.uk and www.defra.gov.uk.

NOTES TO EDITOR:

1. Images of the symptoms of both phytophthora species are available on the Forestry Commission website: http://www.forestry.gov.uk/planthealth.

2. There are more than 220,000 hectares of oak trees in Britain, accounting for almost 10% of all woodland tree species.

Colin Morton: 0131 314 6249