We are urgently working to contain and research the spread of a disease caused by the fungus-like pathogen Phytophthora ramorum (P. ramorum) which is affecting plantings of Japanese larch in Devon, Cornwall and Somerset.
Background
P. ramorum was first found in the UK in 2002 and until 2009 in the woodland environment it had largely been associated with rhododendron species that act as a host from which spores are produced. Only a small number of trees had been infected, and all of them had been standing close to heavily infected rhododendron, which is common in many British woodlands.
However, in August 2009 P. ramorum was found on a small number of dead and dying Japanese larch (Larix kaempferi) in South West England. This caused particular concern because some of the affected trees were not close to infected rhododendron. Subsequent testing at sites in north and west Devon and west Somerset confirmed the presence of P. ramorum in mature Japanese larch as well as species in its under-storey, including sweet chestnut, beech, birch, oak, Douglas fir and Western hemlock. On some sites there is little or no rhododendron present. These findings highlighted a significant change in the dynamics of the disease experienced previously, when tree infection had only occurred in close proximity to infected rhododendron. It is now known that Japanese larch can produce very high quantities of disease-carrying spores when actively growing in spring and summer, at much higher levels than those produced by rhododendron. These can be spread significant distances in moist air.
What we are doing
The Forestry Commission’s primary concern is to protect the health of Britain’s trees, woods and forests. We are working closely with colleagues in Forest Research and the Food & Environment Research Agency (Fera) to survey, understand better, contain and control the disease and to minimise its impacts on woodlands, the forestry sector and the wider environment.
The current strategy to control and contain the spread of P. ramorum is to reduce levels of inoculum (infective spores) in the environment by felling infected plantings of the principal sporulating host, Japanese larch, as rapidly as possible. Fera is also continuing its programme of clearing infected rhododendron from woodland and other sites.
Current actions include:
- a programme of aerial survey in the South West, Wales and western Britain (where the climate favours the disease) to identify possible sites of infected larch. This is followed by contacting owners, site visits to check symptoms and laboratory testing to confirm or otherwise the presence of P. ramorum;
- a programme of clearance where disease is confirmed, on both private and publicly owned sites;
- developing a package of short-term help for private woodland owners affected by the disease. This includes a licence system to enable the movement and processing of timber from affected larch;
- continued scientific research to understand the disease better and the overall risks to our trees, woods and forests, including potential impacts on the UK forestry sector and associated industries;
- further survey of rhododendron by Fera followed up with funded rhododendron clearance agreements where appropriate; and
- encouraging owners to check their woodland, especially larch plantings, for signs of the disease and to report suspicious symptoms promptly. (Owners have a legal obligation under Plant Health legislation to notify the authorities if they suspect the disease is present.)
Symptoms
Information on P. ramorum symptoms is available for symptoms on Japanese larch and Douglas fir, and rhododendron. On Japanese larch, shoots and foliage can be affected and are visible as wilted, withered shoot tips with blackened needles. The infected shoots shed their needles prematurely. Trees with branch dieback may have numerous cankers on their branches and upper trunk that can bleed resin.
Note that in the winter symptoms in larch are much more difficult to spot. However, rhododendron will still exhibit symptoms during this period, so it is important to monitor this as an indicator of disease where it occurs in conjunction with Japanese larch.
For information on the disease and symptoms in other tree and shrub species, visit the Fera website: www.fera.defra.gov.uk/plants/publications/plantPestDiseaseFactsheets.cfm
What should woodland owners and managers do?
- Familiarise yourself with the symptoms and other details. Look on the website www.forestry.gov.uk/pramorum for the latest information.
- Maintain vigilance and inspect your woods regularly, particularly where Japanese larch and/or rhododendron and/or sweet chestnut is present. Please note that we are primarily concerned with plantations of Japanse larch in forests and woodland.
- Follow the recommended biosecurity precautions to minimise the spread of the disease, particularly if you are moving between woods.
- If you suspect your woodland might be infected or you have noticed suspicious symptoms, please report it without delay to the Forestry Commission’s Bristol office, tel: 0117 3721070; email: plant_health_england@forestry.gsi.gov.uk . The details you will be asked for will include:
- name and address;
- contact telephone and email;
- location of the woodland concerned (grid reference, postcode or nearest town);
- approximate area and age of the Japanese larch;
- approximate area of rhododendron (if present);
- whether the rhododendron (if present) is showing symptoms;
- whether there is sweet chestnut present; and
- the approximate date when symptoms were first noticed;
If you are concerned about individual garden, parkland or amenity trees, contact the Forest Research Tree Health Disease Diagnostic & Advisory Service on 01420 23000, ddas.ah@forestry.gsi.gov.uk or visit www.forestresearch.gov.uk/ddas.
If you see symptoms in rhododendron outside of woodland, e.g. parks and gardens, scrub or heathland, please contact Fera on 01904 465625 or email planthealth.info@fera.gsi.gov.uk, mentioning Phytophthora in your report.
