The Forestry Commission has revised the boundaries of the risk zones for Phytophthora ramorum infection of larch trees in Great Britain in the light of recent experience. The revised risk zones map divides Britain into three zones:
• Zone 1 encompasses the general area of higher climatic risk where infection has been found on larch. It previously covered Wales and South West England, but has been expanded to include North West England and a small part of western Scotland;
• Zone 2 takes in remaining areas of higher climatic risk, but where no infection has yet been found on larch; and
• Zone 3 represents areas of lower climatic risk where no larch infections have been found to date.
John Morgan, Head of the Commission's Plant Health Service, explained, "The reasoning behind the change to include North-West England and the area around the island of Mull in Scotland in Zone 1 was the recent confirmation of new infections in Lancashire, Cumbria and Mull."
The zones not only reflect the relative risks, but are also used to guide the handling of applications for felling licences to fell larch trees and the conditions for new approvals of subsequent restocking (replanting) of the felled sites, as explained in the Forestry Commission's Operations Note 23a for England.
Dr Morgan added,"We believe it is prudent to apply the felling and replanting conditions specified in Operations Note 23a to the higher climatic risk zones in the North West of England, and Forestry Commission Scotland is considering whether to apply similar conditions in the highest risk zone in Scotland."
Forestry Commission England and Forestry Commission Wales will not approve new applications for felling larch trees in Zone 1 during winter months when, without needles on the trees, it is more difficult to detect symptoms of ramorum disease. Biosecurity precautions are required as a condition of moving timber from larch woodland that is known to be infected. If the disease status of larch is not known, there is a risk that infected material could enter the wood supply chain without the appropriate biosecurity measures being in place.
The Commission also does not approve the use of larch species as part of any restocking or new planting proposal on sites in Zone 1, and will discourage the use of larch in zone 2. This is because the pathogen can stay viable in soil for several years, causing a high risk of infection in subsequent larch crops. Forestry Commission Scotland is considering whether to apply similar conditions in Scotland.
The zone boundaries are set on main trunk roads or easily identifiable physical features, such as rivers, to ease identification on the ground. They will continue to be reviewed in light of any new outbreaks.
The map and Operations Note 23a are available from the P. ramorum pages of the Forestry Commission website at www.forestry.gov.uk/pramorum .
1. Phytophthora ramorum thrives in most, humid conditions, which is why larch woodland in the wetter, western side of Great Britain is classified as being at higher risk of infection than those in the east. Almost all outbreaks of ramorum disease of larch have occurred in western parts of England, Scotland and Wales.
2. P. ramorum is a 'quarantine' organism. It is not harmful to humans or animals, but its presence on trees or woodland plants must be notified to the Forestry Commission, Fera or the Welsh or Scottish Government, which must take action to contain or eradicate it. Suspected cases in larch trees can be reported to:
• Scotland - email@example.com; tel. 0131 445 2176
• England - firstname.lastname@example.org; tel. 0117 372 1070;
• Wales - email@example.com; tel. 0300 068 0300.
A guide to symptoms is available from www.forestry.gov.uk/pramorum.
3. P. ramorum can infect more than 150 species of plants and trees. It was first identified in the UK in a viburnum plant in 2002, and has since infected a wide range of plants here, including the environmentally important bilberry plant (Vaccinium myrtillus). The 2009 discovery of fatal infection in Japanese larches (Larix kaempferi) in South West England was the first time it had been found infecting a commercially important conifer tree species anywhere in the world.
4. P. ramorum infection causes Japanese larch shoot tips to wilt and needles to turn black and fall prematurely. Cankers that bleed resin can appear on the branches and upper trunk, and the trees can die within a year of the symptoms first becoming detectable. The only known treatment is to fell infected trees, preferably before they next "sporulate" (produce infective spores) to limit further spread of the disease. As a result more than 2 million larch trees in the UK, mostly in South West England, South Wales and Northern Ireland, have been felled since 2009.
5. Larch is a durable, versatile timber that tolerates moisture and resists rotting when used in the ground. These qualities make it well suited for outdoor uses such as fence posts and 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. There is no evidence that P. ramorum harms the timber, so logs from infected trees may be sold into the timber market, provided biosecurity measures are put in place to prevent accidental spread of the disease during timber movements.
6. 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. Japanese larch is the most popular species with industry and end users because of its superior timber properties, but European larch (Larix decidua) and hybrid larch (Larix x eurolepis) are also grown in Britain.