Distribution and etiology of aerial stem infections of Phytophthora ramorum and Phytophthora kernoviae at three woodland sites in the U.K.

Phytophthora ramorum and P . kernoviae sp. nov are recently introduced, invasive pathogens in woodlands in southern Britain. P. kernoviae is a newly discovered taxon, previously referred to as Phytophthora taxon C. Both species aggressively infect foliage and shoots of understory rhododendrons, especially Rhododendron ponticum. From there they can spread aerially to attack the inner bark of tree stems, especially European beech (Fagus sylvatica) and some Quercus species, causing bleeding lesions (Brasier and others 2004). Both species of Phytophthora are under investigation as scheduled risk organisms on trees in the U.K.