First discovered in the UK in 1993 and specific to alder. Causes root collar and stem lesions resulting in crown dieback and rapid tree death. Now widespread in the riparian ecosystems of the UK where alder commonly grows. This disease is a hybrid of other Phytophthora strains and is spreading across Europe as a ‘hybrid swarm’. Some of the variants are extremely damaging and ‘pose a serious threat to alder and the stability of riparian systems’ (Forest Research). Incidence is highest in SE England but heavy losses are being reported in Wales, also along Scottish rivers including Dee, Deverson,Duirinish and Spey.