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Ramorum disease, which has caused the early felling of about 2 million Japanese larch trees in the UK, has now been found infecting the European larch species for the first time.
Scientists from the Forestry Commission’s research agency have confirmed infection by the pathogen Phytophthora ramorum in a European larch (Larix decidua) in woodland near Lostwithiel in Cornwall, south-west England, in an area with infected Japanese larch trees nearby.
Ben Jones, the Forestry Commission’s Phytophthora operations manager, said,
“Although it is bad news that this lethal pathogen has proved able to infect yet another tree species, it was not entirely unexpected, given the physiological similarities between European and Japanese larch.”
Britain’s woodland owners and managers have been on high alert since P. ramorum was first found infecting and killing thousands of Japanese larch (Larix kaempferi) trees in south-west England in 2009, and Mr Jones added,
“It is too soon to know how susceptible European larch is to P. ramorum infection, or whether it will be a sporulating host, that is, whether it will produce the spores that spread the pathogen; and if it is, how heavily it will sporulate.
“However, in the light of this development we are urging woodland managers once again to be diligent about inspecting their trees regularly for signs of disease and decline, and to report any suspicious symptoms of cankers or dieback on larch to us.
“We will be resuming aerial surveys soon, after the trees have flushed with new needles, to look for larch woodlands with symptoms of dieback, and following up with ground inspections to identify the cause of the symptoms."
The symptoms of P. ramorum infection in larch include excessive resin bleeding, sunken or cankered areas of bark, wilting of the needles with the tree canopy turning grey, and branch and shoot dieback with a distinctive ginger colour.
- The Forestry Commission has published a comprehensive update report on the outbreak of P. ramorum on larch, which is available from a link at www.forestry.gov.uk/pramorum. And two grant aid packages for helping the owners of infected larch trees have been extended until March 2012 - details are available from the same pages.
NOTES TO EDITORS:
- P. ramorum was first identified in the United Kingdom in a viburnum plant propagated in a garden centre in West Sussex in 2002. It has since been found infecting a wide range of plants and trees in all four countries of the United Kingdom and the Isle of Man. Until recently it had mostly affected shrubs such as rhododendron, camellia and viburnum, but only a limited number of trees; and from late 2008 the environmentally important bilberry plant (known as blaeberry in Scotland and winberry in Wales). Globally it is known to be able to infect more than 150 host species.
- In August 2009 P. ramorum infection was confirmed in Japanese larch trees in a mix of Forestry Commission and privately owned forests in South West England. It was then confirmed in forests in Wales in 2010, mostly in public woodland managed by Forestry Commission Wales in south Wales. It was also found in a small larch plantation on the Craignish Peninsula in Argyll, Scotland, at one site on the Isle of Man, and at nine sites in Northern Ireland. This was the first time it had been found infecting a commercially important conifer tree species anywhere in the world.
- Tree mortality is rapid – P. ramorum appears to be able to kill Japanese larch trees within one growing season after its presence is first detectable, which, compared with other tree diseases, is fast acting.
- Infected Japanese larch trees produce particularly high numbers of the inoculum that spreads the disease – much higher than the level produced on Rhododendron ponticum, one of the most commonly infected plant species in Britain. This means the disease can quickly affect a large number of trees and shrubs. The pathogen can be spread in mists, rain and air currents, and Forest Research scientists have advised that the most effective means of preventing the spread of the disease is to fell infected trees and plants to kill the living plant material on which the pathogen depends.
- P. ramorum is a ‘quarantine’ organism under European Union law, and its presence on trees or woodland plants must be notified to the relevant authorities (Forestry Commission, Fera, Welsh Assembly Government or Scottish Government), who must take statutory action to contain or eradicate it.
- P. ramorum causes the disease known as "sudden oak death" in the USA, where a different mating type of the pathogen has killed millions of American native oak and tanoak trees in California and Oregon. However, its American common name is a misnomer in Britain, where laboratory tests have shown that our two native species of oak, sessile and pedunculate oak, are much more resistant to P. ramorum than their American cousins. Fewer than five native oak trees have been confirmed with P. ramorum infection in Britain, and the generic term Ramorum disease is preferred here.
- P. ramorum should not be confused with acute oak decline (AOD), which is a separate disease affecting oak trees in the Midlands and parts of Wales and South East England, and in which a newly discovered bacterium species appears to be involved.
- P. ramorum has not been confirmed in any hybrid larch (Larix x eurolepsis), which is also planted in Britain. Larch is a durable, versatile timber that tolerates changes between wet and dry conditions very well, and resists rotting when used in the ground. It is therefore in demand for outdoor uses such as fence posts, fence panels, exterior wall cladding, boats, sheds and furniture, as well as indoor uses such as flooring and chipboard. It is easily stained, worked and finished, and P. ramorum does not harm the timber.
- There are about 134,000 hectares (331,000 acres) of larch woodland in Britain, equivalent to about 5 per cent of the total woodland area. Although precise figures are not available for the areas planted in each of the three larch species used in Britain, Japanese larch is the most popular with the timber industry because of its superior timber properties.
- P. ramorum in Great Britain overall and P. ramorum research - Charlton Clark, 0131 314 6500;
- P. ramorum in England – Stuart Burgess, 0117 372 1073;
- P. ramorum in Wales - Mary Galliers, 0300 068 0300;
- P. ramorum in Scotland – Steve Williams or Paul Munro, 0131 314 6508/7.