Phytophthora lateralis

Identify and diagnose the deadly conifer pathogen Phytophthora lateralis

Disease overview

P. lateralis has been killing the evergreen conifer Lawson cypress (Chamaecyparis lawsoniana) in North America for decades. But it has recently spread to Europe – and in 2010 it was reported in Britain for the first time.

Although P. lateralis infects Lawson cypress almost exclusively, other reported hosts in the UK include Chamaecyparis pisifera, Thuja occidentalis and Thuja plicata. It typically attacks the roots and lower stem but can occasionally attack the stem, branches or foliage.


  • Trees decline quickly
  • Foliage turns to rust-red then most or all of the crown becomes a dull bronze
  • Isolated patches of bronze or brown foliage in the crown shows that the stem or branches are infected
  • Phloem (inner bark) becomes discoloured

Find out more about the symptoms, with pictures to aid diagnosis.

If you suspect P. lateralis in a tree, our Tree Health Diagnostic and Advisory Service can confirm infection.

Disease management

Access the Forestry Commission P. lateralis pages for advice on managing this disease.

Related resources 


Dr. Sarah Green