Phythopthora lateralis: Symptoms

Lawson's cypress tree (Chamaecyparis lawsoniana) infected with Phytophthora lateralis at Balloch Castle Country Park, West Dunbartonshire, ScotlandWhen infected with Phytophthora lateralis, a Lawson cypress tree will decline rapidly. Its foliage will first turn to rust-red and then dull bronze over most or all of the crown.Although the pathogen typically attacks tree roots, it can also occasionally attack the stem or branches. Discrete aerial infections produce large, isolated patches of crown foliage that turn bronze or brown.

A Lawson's cypress (Chymaecyparis lawsoniana) suspected to be infected with Phytophthora lateralis standing next to healthy Lawson's cypress trees in Balloch Castle Country Park, West Dunbartonshire, Scotland 

If you suspect a tree has P. lateralis infection, first confirm the tree species [Link to sub-page on identifying different conifer trees]: brown foliage is common in Leyland cypress for a variety of reasons, but P. lateralis is not known to infect this species. 


Lawson's cypress (Chymaecyparis lawsoniana) trees at different stages of suspected infection by Phytophthora lateralis, in Balloch Castle Country Park, West Dunbartonshire, Scotland. The tree in the foreground is at a more advanced stage of the infection than the tree in the backgroundYou can identify infected conifers by cutting away the outer bark at the base of the tree to reveal the phloem or inner bark. Healthy phloem is a cinnamon brown colour, but becomes clearly discoloured following P. lateralis infection.

How we can help

  • Find out how to take a sample [Link to sub-page on collecting a sample] to identify a Lawson cypress infection
  • Contact our Tree Health Diagnostic and Advisory Service to help you identify Lawson cypress and confirm infection from samples