WSU Extension


Annosus root rot 
Phytophthora root rot 
Hemlock scale 
Hemlock woolly adelgid 

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Caption: Annosus root rot decayed wood with black flecks
Photo by: B.M. Johnson
Hemlock : Annosus root rot
(revision date: 4/20/2015)

Annosus root rot is caused by the fungus Heterobasidion annosum. This native soil pathogen is often in large old tree stumps. It can live several decades as a saprophyte on stumps and roots. Infection is mainly from airborne spores produced by conks on or in old stump hollows. Spores infect freshly cut stump surfaces or trunk wounds. Infection spreads from stumps to roots of healthy seedlings or trees that contact infected wood. Root infections may lead to root and lower bole decay, and trunk infections lead to stem decay. Infected roots may be covered by mycelium of the fungus, but usually no mycelium or conks are present. Decayed wood may be laminated or stringy with black flecks. In later stages of root infection, affected trees show crown yellowing and reduced branch growth. Trees oftentimes die as a result of windthrow. Bark beetles also often infest Annosus-infected trees. Newer trees growing between stumps of old trees are especially susceptible, and pockets of this disease increase in areas where the disease goes unnoticed and/or untreated.
Management Options

Non-Chemical Management
  • Stumps may be excavated between rotations, preventing spread
  • Remove and destroy infected trees and roots systems if possible
  • In mixed-species areas, favor resistant species (cedar, pine, Nordmann fir, hardwoods) when thinning or harvesting
  • Avoid wounding tree roots and trunks
  • Trichoderma spp. have been tried as a biological control with positive results on stumps of some tree species and are readily available.
Select non-chemical management options as your first choice!

Chemical Management

None recommended


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Caption: Annosus root rot decayed wood with black flecks
Photo by: B.M. Johnson
Caption: Annosus root rot stump symptoms
Photo by: B.M. Johnson
Caption: Annosus root rot fruiting bodies exuding from trunk
Photo by: G.A. Chastagner
Caption: Annosus root rot trunk symptoms
Photo by: G.A. Chastagner