See:
Fir, Douglas and True - Stem Decays (Heart Rots)
Fir, True (Abies spp.) - Heterobasidion Root Disease
Cause Stem decay in living trees is caused by various fungi that enter trees through wounds or small branches. Schweinitzii root and butt rot, Phaeolus schweinitzii (sometimes called the cow pie fungus), is the most important decay in old-growth Sitka spruce. Decay fungi usually do not kill trees but trees, which are affected, are structurally weakened and more likely to break during storms or harvest. Most likely the problem when an old Sitka spruce tree breaks at the butt and has a dark-brown cubical decay. Decayed trees can be a serious hazard when near roads, buildings or developed recreation areas.
Wounds can activate dormant infections and provide openings for spores to create new infections. Basal wounds generally have more decay than upper stem wounds. Older trees tend to have more decay as well. Living trees will actively compartmentalize decay columns limiting the amount within the stem. The CODIT model/principle (compartmentalization of decay in trees) is used by certified arborists to manage landscape trees with decay.
Symptoms Brown cubical decay of the heartwood. The fungus produces a large yellow to brown conk with soft velvet top develop on the stem. The conk has a short stalk when growing on the ground (and looks like a cow pie) but is bracket-like when growing on a tree. Basal resinosis or pitching (large exudations of pitch at the base of the stem at or below the root collar) may also occur. Might be confused with Heterobasidion root rot if fruiting bodies are not present.
Cultural control The primary management tactic is to prevent tree wounds.
- Avoid spring and early summer logging, when bark is soft and loose.
- Mark "leave" trees rather than trees to be cut so that leave trees are easier to distinguish.
- Plan and mark skid trails before logging.
- Log skid trails first, then limb and top trees before skidding.
- Use directional falling and fell to openings.
- Remove slash within 10 feet of "leave" trees to reduce damage from natural or prescribed fires.
Reference Shaw, D.C., Oester, P.T. and Filip, G.M. 2009. Managing Insects and Diseases in Oregon Conifers. Oregon State University Extension Service. EM 8980.