Host of the month - Lawson cypress
‘Host of the month’ is a series of Blogs and PDF’s that highlight a tree host and their associated priority pests and diseases that are best seen and recorded in that month. For February we’re looking at Lawson cypress (Cupressus lawsoniana) and Phytophthora lateralis.
Lawson cypress is a member of the Cupressaceae, the second most species rich family of conifers. Both the scientific and common names commemorate Peter Lawson, the Scottish nurseryman who introduced it to cultivation. In its native range, from the southern coast of Oregon into northern California, it is the source of high value timber which is shipped to Japan for use in shrines and coffins. It was introduced to the UK in 1854 and although it has a very minor role in forestry it has become a very important horticultural species. There are at least 559 cultivar names covering a diverse range of forms and foliage colours that are found in parks and gardens across the British Isles. The foliage is scale-like and has a distinctive aroma when crushed, often described as parsley-like. When backlit the scale leaves can be seen to contain a spindle-shaped translucent resin gland, a useful ID feature.
Credit: Matt Parratt
Priority pathogen – Phytophthora lateralis
Lawson cypress is the key host for P. lateralis, an aggressive fungus-like pathogen thought to originate in Asia that was first identified in the UK in 2010. It has also spread to the native range of Lawson cypress in the USA where it has killed trees of all ages and has destroyed entire stands of the species in some habitats.
This pathogen spreads via spores in soil or water, and primarily attacks the roots and leads to lesions, discoloration of foliage, dieback, and eventually tree death. Early signs include discoloration, initially with some yellowing, but quickly progressing to a reddish-ginger and finally a dull bronze as the tree dies. These symptoms are caused by dark coloured lesions below the bark which cut off the supply of water and nutrients to the upper parts of the tree. Symptom progression is rapid and it is extremely rare for an infected Lawson cypress to recover.
Credit: Crown copyright, Forest Research.
The pathogen spreads via spores in soil or water, and primarily attacks the roots and leads to lesions, discoloration of foliage, dieback, and eventually tree death. Early signs include discoloration, initially with some yellowing, but quickly progressing to a reddish-ginger and finally a dull bronze as the tree dies. Other Phytophthora species can also infect Lawson cypress and result in the same symptoms above ground so definitive identification requires laboratory analysis.
December is an ideal time to seek out Lawson cypress trees and see if you can identify any signs and symptoms of Phytophthora lateralis. This Phytophthora is a priority pathogen so please report possible sightings via TreeAlert. Healthy tree data is equally important so please do report those too.