Last year, 876 hectares of Japanese larch trees were found to be infected by an outbreak of ramorum disease in Wales.
During the winter, Forestry Commission Wales put surveys of woodlands on hold as, once the larch trees have dropped their needles, it is difficult to spot symptoms in infected trees.
Since the trees regained their needles in late spring, Forestry Commission Wales surveyors have again been out in force checking woodlands to find out how far ramorum disease has spread.
Initial findings from these surveys indicate that this fatal tree disease has infected a further 227 hectares of larch trees in Wales.
Owen Thurgate, Phytophthora Project Manager at Forestry Commission Wales, said, "The worst case scenario would have been to have found the same number, or even more, trees infected by ramorum disease this year as last year.
"The advice of Forest Research scientists to prevent the disease’s spread is to fell infected trees to kill the living plant material on which the Phytophthora ramorum pathogen depends.
"Whilst it is therefore worrying that we will have to fell a large number of infected trees again this year, it would seem that our decision to swiftly fell infected trees last year has played a key role so far in managing this major outbreak."
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.
In autumn, infected Japanese larch trees produce huge quantities of the spores that cause ramorum disease. The disease can therefore quickly affect and often kill large numbers of these trees within a year of symptoms first being detectable.
Weather also plays a role in the spread of ramorum disease as the spores seem to travel best during damp conditions.
"Last year, we found that the dry autumn helped to reduce the spread of the spores that cause ramorum disease," said Owen.
"We therefore expect that the disease’s progress will depend on the weather this autumn, too, so the drier the conditions later this year, the better."
Forestry Commission Wales will continue to undertake surveys looking for the symptoms of ramorum disease until October.
In the meantime, the felling of trees that have been diagnosed with ramorum disease so far this year has begun.
Ramorum disease does not harm the timber, and biosecurity measures have been put in place to allow logs from infected trees to be taken to sawmills without spreading the pathogen to other trees or plants.
"We are determined to minimise the impacts of ramorum disease on woodlands and the forest industry, and the support of woodland owners in looking out for early signs of infection will continue to play a key role in our disease management strategy," said Owen.
Ramorum disease is not harmful to humans or animals, and all public woodlands remain open to visitors, except in areas where felling operations are taking place, which are temporarily closed for safety reasons.
Owen said, "We are appealing to everyone who works in or visits the affected forests to help us contain this outbreak by observing some biosecurity precautions so that the pathogen is not inadvertently spread on boots, bicycle or vehicle wheels, tools or machinery.
"Signs explaining these simple precautions will be placed at the entrances to forests where ramorum disease is present."
Woodland owners or managers in Wales who suspect infection in their trees should report it to Forestry Commission Wales’s Grants & Regulations office at Clawdd Newydd, Ruthin, Denbighshire, LL15 2NL Tel: 0300 068 0300, e-mail: email@example.com.
Further information about Phytophthora ramorum is on the Forestry Commission’s website at www.forestry.gov.uk/pramorum.
NOTES TO EDITORS
1. Ramorum disease of larch is caused by the pathogen Phytophthora ramorum (P. ramorum), which can infect more than 150 species of plants and trees.
2. P. ramorum was first identified in the United Kingdom in a viburnum plant in a garden centre in West Sussex in 2002. It has since been found infecting a wide range of plants and trees throughout the UK. Until recently it had mostly affected shrubs such as rhododendron, camellia and viburnum, but only a limited number of trees; and from late 2008 infection has been found in the environmentally important bilberry plant (Vaccinium myrtillus - known as blaeberry in Scotland and winberry in Wales).
3. In August 2009 P. ramorum infection was confirmed in Japanese larch trees in South West England. This was the first time it had been found infecting a commercially important conifer tree species anywhere in the world, and has since been confirmed in larch trees in all four countries of the UK as well as the Republic of Ireland.
4. 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. In Japanese larch, it causes shoot tips to wilt and needles to turn black and fall prematurely. Cankers that bleed resin can appear on the branches and upper trunk.
5. Infected Japanese larch trees produce particularly high numbers of the spores that spread the disease – much higher than the level produced on Rhododendron ponticum. 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.
6. 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.
7. 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.
8. P. ramorum does not harm the timber, and logs from infected trees can be sold into the timber market, subject to biosecurity measures to ensure that their movement does not further spread the disease.
9. Larch is a durable, versatile timber that 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 as well as flooring and chipboard.
10. There are about 134,000 hectares (331,000 acres) of larch woodland in Britain: about 5 per cent of the total woodland area.
11. P. ramorum is not harmful to humans or animals, and all public woodlands remain open to visitors, except in areas where felling operations are taking place, which are temporarily closed for safety reasons.
12. P. ramorum causes the disease known as "sudden oak death" in the USA, where a different mating type has killed millions of North 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 native sessile and pedunculate oaks are much more resistant to P. ramorum than their American cousins, and fewer than five native oak trees have been confirmed with P. ramorum infection in Britain. Therefore the generic term ‘ramorum disease’ is used in Britain instead of ‘sudden oak death’.
13. 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 in Great Britain overall and P. ramorum research - Charlton Clark, 0131 314 6500;
• P. ramorum in Wales - Mary Galliers, 0300 068 0300; firstname.lastname@example.org
• P. ramorum in England – Stuart Burgess, 0117 372 1073 or Becci Turner 0117 9066030;
• P. ramorum in Scotland – Steve Williams or Paul Munro, 0131 314 6508/7.