Phytophthora lateralis

This is an Oomycete, not a true fungus but an honorary one. It spreads via zoospores that literally swim through the soil and infect the roots of hosts. Zoospores cause root and collar lesions, then hyphae will spread on the larger roots and root collar where they kill the inner bark (Hansen, 2007). It thrives in areas with wet soils such as stream drainages, and may be native to northwestern North America. The only known hosts for this pathogen are Port Orford cedar (Chamaecyparis lawsoniana) and Pacific yew (Taxus brevifolia), with the cedar being much more susceptible than the yew (Murray and Hansen, 1997).

The disease was first discovered in Seattle native plant nurseries in the 1920’s and has historically been limited to Washington, Oregon, and California. However, recently P. lateralis has been found in Taiwan in old growth forests of Chamaecyparis obtusa. Also it has been found in France, Scotland, Northern Ireland, and the Netherlands on C. lawsoniana which is planted as an ornamental throughout Europe.