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A highly destructive tree disease has been found on larch trees in South East England for the first time.
Ramorum disease, caused by the fungus-like pathogen Phytophthora ramorum (P. ramorum), has been confirmed in larch trees in two woodlands: one in West Sussex, and the other in Surrey. The Forestry Commission first became concerned when larch trees showing symptoms were spotted during a helicopter survey of the region in June, and ground-based checks confirmed the surveyors' suspicions.
Ramorum disease has been responsible for the premature felling of more than 3 million larch trees in the United Kingdom since it was first found killing larches in the West Country in 2009. Most cases have occurred in the wetter, western parts of Great Britain as well as Northern Ireland, the Republic of Ireland and the Isle of Man. This month’s confirmation that the disease has reached South East England is the first time it has been recorded so far east, although the organism has previously been found in the region infecting other plants, such as rhododendron.
Alison Field, South East England Director for the Forestry Commission, explained,
“Like all Phytophthora organisms, P. ramorum thrives in the kind of wet weather we have had this year. It is also significant that both of the affected woodlands are close to areas where rhododendron shrubs have been infected with P. ramorum as well, so although this is bitterly disappointing news, it is understandable that it has spread into local larch trees.
“Sadly, the only treatment to prevent this disease from killing millions more larch trees is to fell the infected trees as quickly as possible, before they can produce the spores that can be spread by wind and mist to infect more trees.”
The Forestry Commission has issued statutory “plant health notices” to the affected owners, requiring them to fell the infected larch trees and others nearby, and Ms Field added,
“We are very grateful for the rapid response of the woodland owners affected to fell their trees as quickly as possible to remove the threat to other woods and woodland owners in the area.
“I would urge all woodland owners in the South East to inspect their trees regularly for signs of ill health, and to report anything suspicious. Those who have rhododendron plants in their woods or gardens should keep a close eye on them too, because infected rhododendron can also produce millions of the spores which spread the disease."
The Commission's aerial surveillance team was flying over South East England again this week to check for any further signs of diseased trees.
Further information about P. ramorum, including guidance to recognising the symptoms, is available on the Forestry Commission website at www.forestry.gov.uk/pramorum.
Suspected cases in England can be reported to firstname.lastname@example.org or by telephone to 0117 372 1070.
• Forestry Commission tree health news can be followed at www.twitter.com/treepestnews .
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 Japanese 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 authorities (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. However, SOD is a misnomer in the UK, where laboratory tests have shown that our native sessile and pedunculate oaks are much more resistant than their American cousins, with only a tiny few confirmed infected. Therefore the generic term ‘ramorum disease’ is used in the UK instead of ‘sudden oak death’.
- Ramorum disease/sudden oak death should not be confused with acute oak decline (AOD), which is a separate condition affecting oak trees in the Midlands, East Anglia and parts of Wales and South East England, and in which newly identified species of bacteria are involved.
- 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 134,000 hectares (331,000 acres) of larch woodland in Great Britain: about 5 per cent of the total woodland area.
- There are about 640 hectares (1600 acres) of larch woodland in Surrey; about 770ha (1900 acres) in West Sussex; and 5300ha (13,250 acres) overall in South-East England, or about 2.3 per cent of the region's total woodland area.
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