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Phytophthora ramorum

Phytophthora ramorum was first identified in the mid-1990s as the cause of widespread devastation of wild oak trees in California and Oregon, USA (which earned it the name 'Sudden oak death'). The pathogen was subsequently found in the nursery trade in North America in 2001.

In Europe, including the UK, P. ramorum was initially found mainly on container-grown Rhododendron, Viburnum and Camellia plants in nurseries. It was first detected in the UK in 2002, when emergency measures were introduced. The initial measures included destruction of infected plants, a ban on imports of susceptible material from affected areas of the USA, and notification of movements of susceptible nursery stock. These measures were notified to the EU Standing Committee on Plant Health, which agreed EU-wide emergency measures in November 2002, based largely on the UK's action. Those measures are still in place.

Rhododendron species, particularly R. Ponticum growing in the wild was found to be an important host for the organism and was thought to be the principal means for spread of disease, leading to the first findings in native trees. In January 2009 the first finding in the wild of P. ramorum on the heathland plant Vaccinium myrtillus (bilberry) was confirmed at a site in Staffordshire. Most recently, in August 2009, the pathogen was identified on Japanese larch trees at sites in Somerset, Devon and Cornwall. Since then it has been found extensively in larch plantations in the south-west, in Wales and in south-west Scotland, leading to the felling of large areas.

Useful information and further reading
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