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The Forestry Commission has given information about the incidence of new cases of ramorum disease of larch trees detected in England this year. The disease is caused by the Phytophthora ramorum pathogen.
Aerial surveying of high-risk areas of England has detected up to 525 hectares of larch woodland as possibly infected, representing an increase in known infected area of up to 26 per cent. There are 44,000ha of larch woodland in England, and Andrew Smith, Head of Sustainable Forest Management for Forestry Commission England, said,
“These figures are positive insofar as they do not show the level of progression being experienced in other parts of the UK, and the great majority of larch in England remains healthy.
“They are still subject to checking from the ground, and the exact figure, based on previous years’ experience, could be as much as 30 per cent lower than this, as other causes are confirmed for some of the symptoms seen from the air.
“However, there is no room for complacency. These data show regional variations in spread and, overall, a moderately greater degree of spread than we’ve found at this stage in previous years. This is not surprising given last year’s exceptionally wet weather, which was conducive to spread of the disease.”
Mr Smith added that Forestry Commission England would continue with its current approach to controlling the disease. This requires the felling of infected trees, and the felling of neighbouring trees out to a radius of 100m from infected trees. Evidence shows that this is the most effective way of reducing the risks of spreading the disease further and minimising wider environmental impacts.
Mr Smith cited the example of Devon, where, “despite having some of the first cases four years ago, about 80 per cent of larch trees remain healthy, which indicates that the current strategy and prompt action by the sector is helping to abate spread of the disease”.
There has been a greater increase of disease in North West England compared to previous years, with the new findings split almost equally between North West and South West England. The Commission is working closely with stakeholders to minimise the impacts of the disease and associated control measures in that part of the country.
He thanked woodland owners for their co-operation with the policy, saying that compliance with statutory notices to fell infected trees had been “extremely good”, with more than 90 per cent of owners complying.
Further information about ramorum disease, including a map of confirmed cases, is available from www.forestry.gov.uk/pramorum .
NOTES TO EDITOR:
- P. ramorum can infect more than 150 species of plants and trees. It is particularly serious in Japanese larch trees, which produce huge quantities of the infective spores which spread the disease. These can be spread from tall trees by the wind and in moist air currents, and the only available treatment to control the disease is to fell the trees, preferably before they next sporulate (produce spores).
- P. ramorum was first identified in the UK in a viburnum plant in West Sussex in 2002. It has since been found infecting a wide range of plants and trees throughout the UK. Until 2008 it mostly affected plants such as rhododendron, camellia and viburnum, and only a limited number of trees. However, since late 2008 infection has been found in the environmentally important bilberry plant (Vaccinium myrtillus - known as blaeberry in Scotland and winberry in Wales), and in larch trees since 2009.
- Infected larch trees die quickly – P. ramorum appears to be able to kill Japanese larch within a single growing season after its presence is first detectable. In Japanese larch, it causes shoot tips to wilt and needles to turn ginger and black and fall prematurely. Cankers that bleed a white resin can appear on the branches and upper trunk.
- The European Commission has adopted emergency measures which regulate P. ramorum as a ‘quarantine’ organism so that its presence on trees or woodland plants must be notified to the relevant plant healthauthorities (Forestry Commission, Fera, Welsh Government, Scottish Government and Northern Ireland Department of Agriculture & Rural Development), who must take statutory action to contain or eradicate it.
- P. ramorum is not harmful to humans or animals, and all public woodlands managed by the Forestry Commission remain open to visitors, except where felling operations are taking place, when they are temporarily closed for safety reasons.
- P. ramorum causes the disease known as "sudden oak death" (SOD) in the USA, where a different mating type of the pathogen has killed millions of North American native oak and tanoak trees in California and Oregon.
- P. ramorum does not harm the timber, and logs from infected trees can be sold into the timber market, subject to biosecurity measures to prevent further spread during timber movements. Larch is a durable, versatile timber which tolerates changes between wet and dry conditions very well, resists rotting when used in the ground, and is easily stained, worked and finished. It is therefore in demand for outdoor uses, flooring and chipboard. There are about 133,000 hectares of larch woodland in Great Britain: about 5 per cent of the total woodland area.
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