Two cases of a new pathogen that could seriously affect trees have been found in native English oak (Quercus robur) trees in a wood near Redruth in Cornwall. This is the first discovery of fungal disease caused by this Phytophthora species in native oak trees in Britain.

The pathogen is related to Phytophthora ramorum, known in the USA as Sudden Oak Death because of the widespread blight it has caused on American oak species. However, until now, native British oaks have proved to be resistant to both pathogens. Since the first discovery of P. ramorum in Britain early in 2002, neither laboratory tests nor painstaking surveys of more than 1500 woodland and forest sites across Britain have established any susceptibility of native oak trees to the deadly fungus.

Although P. ramorum is known to exist in more than a dozen countries throughout Europe, the new Phytophthora is so far thought to be specific to Britain. A major concern is that laboratory tests and observations in the wild indicate that it is more aggressive, and much faster spreading, than P. ramorum. Rhododendron, the main host and source of infection, succumbs in just a few weeks, rather than months.