When 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.
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.
You 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