Jones said analysis suggests that it is likely to spread and could eventually affect the majority of larch in Wales.
Elin Jones said climate modelling by the Forestry Commission’s Forest Research (FR) scientists had shown that the greatest risk was in the west of Britain, a fact reflected by the distribution of cases to date.
Jones said: "In the autumn of 2009 the FC confirmed that the dynamic of P. ramorum had altered significantly when Japanese larch was identified as a new and prolific sporulating host – producing inoculum at far greater levels than any other known host and it is now seen as the greatest risk of spreading the disease in the UK. The key to containment remains in trying to reduce the inoculum levels by prompt felling and removal of infected trees.
"Larch is a deciduous conifer so since bud burst in late April 2010 the FC have undertaken aerial surveys to establish the spread of trees with disease symptoms. On 18 May 2010, suspicious sites were identified in south Wales and the Forest of Dean and following further surveys, as of 15 June, the disease has been confirmed in the Vale of Glamorgan and Neath Port Talbot and Bridgend County Boroughs. So far, the infected sites are all on the Welsh Assembly Government owned woodland estate.
"In addition to an FCW survey of all larch stands in south Wales, the Food and Environment Research Agency (Fera) are organising wider monitoring throughout all of Wales during July, including a three day helicopter survey to try to identify the spread of the disease.
"The total forest area where infected trees have been reported is around 6,251 hectares of which 464 hectares have been identified as infected with the disease. The Assembly Government woodland estate covers an area of approximately 126,000 hectares across Wales. Most of the larch in Wales is situated on the Assembly Government woodland estate and the species accounts for approximately 10% of the Assembly Government woodland estate.
"The scale of the infection has resulted in an assessment of FCW’s programme priorities to enable an effective response and to manage the possible long term impacts. FCW is enabling collaborative working across the affected area and between private woodland owners, private sector agents, timber processors and the relevant public sector bodies.
"Collaboration with private woodland owners and their representative groups is critical due to the lack of accurate private woodland ownership data, the fragmented ownership of many small woodlands and the need for the prompt co-operation of owners to ensure that the disease can be contained. It is critical that they look for the disease, self declare and if necessary act promptly.
"FCW has provided training to its field staff on how to recognise P. ramorum and will be providing this to private woodland owners and managers over the next few weeks.
"FCW has implemented bio-security measures for contractors and FCW staff on all infected sites on the public estate. The woodland estate remains open but signs have been erected at all entry points to affected woodlands to inform the public of the infection and ask for their help in controlling it’s spread, for example, by keeping to designated paths.
"A letter requiring FCW to fell the infected trees will shortly be issued by the FC Plant Health Branch (Edinburgh) under the Plant Health (Forestry) Order 2005. This will initiate a clearance programme on the Assembly Government woodland estate.
"The FC will use its GB wide regulatory powers to compel owners to fell infected trees. Whilst it is not possible under the legislation to compensate owners for loss of timber income, the FC can fund steps to assist in delivering the desired outcome of preventing the spread of this infection.
"The financial impact of the disease cannot yet be quantified because FCW are still assessing how widespread the infection is and do not as yet, know how marketable the infected material will be (sawmills are being advised about the licensing requirements). The income from older infected stands may cover some of the costs but there is the cost of clearing younger crops from which there will be no marketable produce.
"The clearance programme (which represents 13.8% of the annual harvesting total on the Assembly Government estate) is likely to have an impact in terms of the woodland estate’s current species composition but FCW will seek to replant the affected sites with species that add diversity and which may also be less susceptible to future outbreaks of damaging pathogens.
"The costs to date have been borne out of the FCW and Fera budget. However, if further significant funding is required to deal with this disease there may be an impact on the delivery of current woodland programmes but these costs will only become clear following the completion and analysis of the Wales-wide survey.