Phytophthora ramorum (P. ramorum) is a fungus-like pathogen of plants that causes extensive damage and mortality to trees and other plants.
In the UK, P. ramorum had mostly been found on plants and shrubs, especially rhododendron, but, in 2009, it was found infecting and killing large numbers of Japanese larch trees in South West England.
This was the first time in the world that P. ramorum had infected and sporulated (reproduced) on large numbers of a commercially important conifer tree species.
In 2010, P. ramorum was found on Japanese larch in Wales (and also in Northern Ireland and the Republic of Ireland).
P. ramorum in Wales
In May 2010, a major outbreak was confirmed in Welsh Government woodlands managed by Forestry Commission Wales in south Wales (the Afan Valley, near Port Talbot; the Garw Valley, near Bridgend; and the Vale of Glamorgan).
Also last year, infected Japanese larch trees were found in a public woodland at Nant yr Arian, near Aberystwyth, and there were three small outbreaks on private sites in Wales. In total, 876 hectares of Japanese larch trees were found to be infected in Wales in 2010.
In spring 2011, surveys recommenced when the larch regained their needles. Initial findings from these surveys indicate that this fatal tree disease has infected a further 227 hectares of larch trees in Wales.
Most of the newly diagnosed trees are in woodlands adjacent to the areas found to be infected with ramorum disease last year in the Afan Valley, near Port Talbot.
Ramorum disease has also been diagnosed in a small number of larch trees at Bwlch Nant yr Arian, near Aberystwyth, where 60 infected trees were felled in 2010, and, for the first time, near the Alwen reservoir in Hiraethog Forest, north Wales.
The outbreak map indicates where infection by P. ramorum has been confirmed in the United Kingdom.
Felling infected Japanese larch trees
Larch trees produce high numbers of the spores that spread the disease, with the result that a lot of larch trees can become infected very quickly.
The aim of felling these infected trees is to limit the production of the spores that spread the disease and therefore minimise the impact of the outbreak -
All landowners with infected trees have been issued with instructions or a notice by the Forestry Commission’s Plant Health Service under the Plant Health (Forestry) Order 2005 to fell the infected areas.
Clearance of infected larch on the Welsh Government's estate is underway.
P. ramorum does not harm the timber and there is no risk of spreading the disease from wood that has been processed.
Working in and visiting infected woodlands
All woodlands managed by Forestry Commission Wales remain open to the public – the only restriction to public access is in areas where felling is underway.