Annosus Root Rot

Annosus root rot typically attacks hemlock and yew species in Pacific Northwest plantings, particularly in mixed-species stands or older timber. The first sign you may notice is scattered tree mortality appearing for no obvious reason, or a tree that suddenly declines despite adequate water and care. The fungus works silently in the root system and heartwood, often leaving the upper canopy green until the damage is severe. In our wet, acidic forest soils, this pathogen finds ideal conditions to persist and spread from tree to tree through root contact.

The reason annosus matters in Western Washington is simple: it kills your most susceptible species with few warning signs until decline becomes obvious. The fungus survives in stumps and can infect fresh wounds on roots and trunks. Your best strategy is to prevent infection rather than treat it; select resistant conifers like cedar, pine, or Nordmann fir when planning mixed stands, and avoid wounding tree roots during site work. If you detect infected trees, removing them entirely (including root systems if feasible) can slow spread, and biological controls using Trichoderma species show promise on fresh stumps.