Phytophthora ramorum detected on Larix kaempferi in the United Kingdom
In the United Kingdom, Phytophthora ramorum (EPPO Alert List) was first found in 2002. In forests and woodlands, the disease has been largely associated with Rhododendron species (mainly R. ponticum) growing in the understorey. But in summer 2009, P. ramorum was detected for the first time on mature trees of Larix kaempferi (Japanese larch) in England (counties of Devon, Cornwall and Somerset). Affected larch trees showed foliar symptoms (wilted, withered shoot tips with blackened needles), and infected shoots shed their needles prematurely. Trees with branch dieback were in some cases showing numerous cankers on their branches and upper trunk that could bleed resin.
Pictures of symptoms on L. kaempferi can be viewed on the Internet:
http://www.forestry.gov.uk/pdf/fcsymptomshandout.pdf/$file/fcsymptomshandout.pdf
This is the first time that stem lesions caused by P. ramorum have been found on a conifer species. Many of the infected L. kaempferi trees were not growing in proximity to rhododendrons which raises the question of how they have become infected. Symptoms have also been found on Tsuga heterophylla (Western hemlock) and a selection of broadleaf species (beech, birch, and some oaks) growing in their vicinity.
Sources
INTERNET (last retrieved in 2010-02)
Forestry Commission website. Phytophthora ramorum. http://www.forestry.gov.uk/forestry/infd-7xvewh