Cedar, Western Red (Thuja plicata)-Pencil Rot (Brown Pocket Rot)

Latest revision: 
March 2023


Cause Stem decay, when found in western red cedar, is usually caused by Postia sericiomollis, a fungus. Old age and stem wounding increase the severity of this disease although wounds are not necessary for establishment of infections. Living cedar trees with brown pocket rot are commonly selected by wood peckers and sapsuckers to develop nest sites. The cavities excavated by these birds are used by many cavity-nesting birds and animals.

Symptoms Stem and butt decay can develop in living trees without external signs of defect. Pockets of decay are initially small and isolated in the heartwood, often separated by several inches of solid wood. Inside the pockets, the decay is a typical brown cubical rot. At first, the wood is light brown and dull in appearance. In the advanced stages, the decay becomes brown or red-brown with cubical cracking. Thin felts of white mycelium may develop in some of the cracks. In cross-section, the decay may appear in concentric rings or arcs as pockets merge.

White or cream-colored fruiting bodies form on dead logs and slash but are not seen on live trees. They form as thin crusts on the outer surface of log ends or dead wood, 6-10 inches across.

Cultural control Consider keeping infected trees for their ecological value.

  • Harvest trees before they are old enough for the fungus to have done much damage.
  • Prevent wounding.

Reference Hagle. S. 2006. Management guide for cedar brown pocket rot. USDA, Forest Service, Forest Health Protection. https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5187351.pdf