Laminated root rot in Douglas fir and grand fir

What it is and which trees it kills

ODF’s fact sheet still uses the old name, Phellinus (Poria) weirii; the Douglas-fir form is now called Phellinus sulphurascens or Coniferiporia sulphurascens, the name in the 2013 Washington State Academy of Sciences report prepared with DNR.

Whatever the label, the fungus works the same way: it decays roots and the butt of the trunk, and ODF estimates about 5 percent of the highly susceptible host type in Oregon and Washington is out of timber production because of it. Washington’s 2024 forest health survey calls it one of the state’s three most common root disease pathogens, even though aerial surveys could map only 200 acres of it because root disease hides under green crowns.

The USDA Forest Service silvics manual lists laminated root rot and shoestring root rot (Armillaria) as the principal pathogens of coast Douglas-fir and “a serious threat” in young stands, which is what most 1960s-to-1990s subdivisions on former timberland in Snohomish, Pierce, Clackamas and Lane counties are.

How it spreads root to root

There are no airborne spores to worry about in your yard. ODF: new trees are infected when their roots contact old infected material, and tree-to-tree spread happens across root grafts and root contacts. The fungus “can survive for decades in large old stumps or roots,” so the infection center on a lot usually predates the house. WSU Hortsense puts it the same way: the disease persists in infected stumps and large roots left in the soil.

That is why a single dead fir rarely tells the story. The pattern is a slowly expanding pocket: one dead tree, two thinning neighbors, a windthrow a few winters later, and healthy-looking trees on the pocket’s edge that are already infected through their roots.

Signs on a standing tree

The symptoms are the symptoms of a tree slowly losing its root system. ODF and WSU list:

• Reduced growth, especially in height: a flattening top and short leader growth compared with neighbors.
• Thinning, yellowing crown that declines over several years.
• Distress cone crops: a heavy load of small cones on a tree that is otherwise failing.
• Windthrow with a root ball. ODF’s phrase: infected trees are often windthrown, “exhibiting a ‘root ball’ where roots have rotted off.” The tree pivots on a short stub of decayed roots instead of snapping.
• Laminated decay in the stump or butt: early decay is a reddish stain; advanced decay separates along the annual rings into sheets, with reddish-brown fungal strands (setal hyphae) between the layers (WSU).

The warning that matters most comes from WSU: infected trees are hazardous and “extremely prone to wind damage,” and west of the Cascades windthrow may happen before any crown symptom shows. If a neighbor’s fir went over with a root ball last winter, your firs on the same slope deserve a look this fall. What an arborist checks, including root-collar excavation and resistance drilling, is on tree risk assessment.

Why stumps must go before you replant conifers

ODF’s management prescription has two halves. First, remove infected trees from the infection center plus susceptible hosts in a 50–75 foot buffer around it (WSU uses 50 feet beyond the last known infected tree). Second, either replant with resistant conifers or immune hardwoods, or remove the stumps and roots so the fungus has nothing left to live in. Neither agency recommends any chemical; WSU’s chemical control line reads “None recommended.”

Stump grinding does not do the second half. A grinder chips the stump to below grade and leaves the lateral roots in the ground, which is exactly where the fungus lives for decades. For a yard you intend to replant with Douglas fir, the honest options are stump and root removal by excavation, or accepting the ground as a no-Douglas-fir zone and planting from the resistant list. The trade-offs, including the 811 locate rule and the difference in disturbance, are on stump removal vs grinding.

Modeled estimate, not quotes (method): grinding runs $150–$450 per stump by diameter ($4–$6 per inch, $150 minimum), while full excavation is priced per job and depends on access; the removal itself for a 50–80 ft fir models at $1,800–$3,600 in Oregon and $1,700–$3,400 in Washington. See stump grinding cost and tree removal cost.

What to plant in an infection center

Use ODF’s resistance list and plant for the site. On the wet side of the Cascades, western redcedar is the resistant conifer that fits most yards, with the caveat that it needs shade and summer water in the hotter lowlands; read western redcedar dieback before you choose it for a sunny lawn. Ponderosa pine suits the drier Willamette Valley floor and east of the mountains. Hardwoods are immune: bigleaf maple, red alder, Oregon white oak, cascara and native cherries all grow in old fir ground. Grand fir, hemlock and more Douglas fir are the one thing not to plant.

If you keep uninfected firs outside the buffer, protect their roots. The silvics manual notes Douglas fir forms a shallow, platelike root system on shallow soils and high water tables, so trenching, grading or parking on the root zone creates the wounds and stress that let root disease and windthrow in.

Permits and next steps

Clearing an infection center usually means several trees at once, and that is where permits bite. Portland regulates private trees 12 inches DBH and larger and limits removals of healthy trees 20 inches and up (PCC 11.40); dead, dying or dangerous trees get the simpler Type A permit, so an arborist’s letter documenting root rot matters. Seattle limits a developed lot to two Tier 4 or three Tier 3–4 removals a year in most zones, allows hazardous trees with replacement, and requires a registered Tree Service Provider for any Tier 1–4 removal (SMC 25.11). Renton allows two significant trees per 12 months without a permit (RMC 4-4-130).

The city-by-city rules are in Oregon tree removal permits and Washington tree removal permits.

1. Map the pocket. Mark dead, thinning and windthrown firs and the healthy ones within 50–75 feet.
2. Get a written assessment from a certified arborist that names the disease; it supports the permit and tells the crew which trees are hazards.
3. Remove the infected trees and the buffer hosts in one mobilization; see tree removal and, for firs over a house, large tree removal.
4. Decide the stump plan before the crew leaves: grind and replant hardwoods or redcedar, or excavate and keep the option of Douglas fir.
5. Call 811 at least two business days before any excavation.

More on the species itself is under Douglas fir; the rest of this site’s species pages are under trees.