Cedar, Incense-Pecky Rot

Latest revision: 
March 2023

Cause The fungus Postia amara caused an important stem decay of incense-cedar in Oregon. Airborne spores infect, through open wounds such as those from fire, large open knots, or broken branch stubs. Trees are particularly susceptible when growing in ravines or other locations favoring surface moisture on exposed heartwood for extended periods of time. Fruiting bodies called conks indicate extensive decay columns. Mostly a problem of older trees.

Symptoms Early rot appears as a yellowish-brown discoloration in the heartwood. Advanced decay consists of round-ended pockets (0.5-12 inches long) containing dark-brown, crumbly, dry rot with numerous longitudinal shrinkage cracks. As decay advances, pockets become more numerous and sometimes nearly coalesce. Rot is confined to the heart wood and usually is not prominent in the butt of the tree.

Annual conks form on the bark above open knots in late summer or fall. Conks are hoof-shaped, 4 to 9 inches wide, and buff-to-bright-yellow in color. When fresh, conks are soft and moist, becoming firm and dry with age. Numerous small angular pore openings cover the underside of the conks. Depressions in the bark caused by woodpeckers searching for insects at a former conk location, called shot-hole cups, are common indicators of infection.

Cultural control

  • Trees with conks or shot-hole cups should be felled and/or removed.
  • In forestry, lower rotation age for incense-cedar.

Reference Goheen, E.M., and Willhite, E.A. 2006. Field guide to the common diseases and insect pests of Oregon and Washington conifers. R6-NR-FID-PR-01-06. Portland, OR. USDA Forest Service, PNW Region.