Phytophthora lateralisis a pathogen that attacks and kills the roots of its host trees, although aerial infections of branches and foliage also occur. It spreads when roots come into contact with the spores in the soil or water. It kills the roots and can extend up the trunk of affected trees and girdle them, leading to tree death. There are two distinct ‘lineages’ of P. lateralispresent in the UK, one that also occurs in the Pacific north west of the USA and another that was first found in Scotland in 2010. Outbreaks of infection have since been confirmed in Lawson cypress trees in South-West-England, Sussex, Yorkshire, Wales, Scotland and Northern Ireland.