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