Laminated root rot: why green Douglas firs fall over in storms

When a Douglas fir with a full green crown goes over in a November windstorm and the root ball comes up looking small and ragged, laminated root rot is a likely suspect. The fungus, Coniferiporia sulphurascens (long known as Phellinus weirii), decays the roots just below the trunk while the needles stay green. Washington State University’s warning is the one to plan around: infected trees can be windthrown before above-ground symptoms are obvious, especially west of the Cascades.

Why a green tree falls

A tree’s crown shows trouble only when the roots can no longer supply water. Laminated root rot works from the other direction: it destroys the anchoring roots first. The Oregon Department of Forestry’s fact sheet describes infected trees as often windthrown with a “root ball” where the roots have rotted off just below the root crown. The tree does not snap; it tips over on a stub.

The USDA Forest Service’s DecAID summary says the same thing about timing: infected trees are frequently blown over before significant symptoms develop, and windthrown trees of all sizes are common in root rot pockets. A fir can carry enough foliage to look healthy from the street and still have lost most of its holding power on one side.

That is why the disease shows up after storms rather than during droughts. Saturated winter soil and a strong gust do the rest.

How common it is in Washington and Oregon

ODF estimates that about 5% of the area of highly susceptible host types in Oregon and Washington is out of timber production because of the disease. Washington’s 2024 forest health report names laminated root rot as one of the three most common and destructive root disease pathogens in the state, alongside Armillaria and Heterobasidion.

The same report shows why the numbers undercount: root rots are hard to see from the air, so the 2024 aerial survey mapped only 200 acres of root disease, while almost 2.8 million acres in Washington and Oregon combined are at risk of losing 15% or more of their basal area to root disease between 2013 and 2027. The disease is in the forests your yard firs came from.

Signs to look for in a yard

ODF and WSU list overlapping signs. In the crown:

• Slowing growth, especially in height, so the top looks flat next to neighboring firs.
• Yellowing, thinning foliage that declines over several years.
• A distress crop of cones on a tree that is otherwise failing.

At the base and in the wood:

• A reddish to brown semicircular stain on a freshly cut stump or root (WSU); DecAID calls it crescent-shaped to semicircular.
• Advanced decay that separates in sheets along the annual rings, the “laminated” rot, with pits in the wood (WSU).
• White to grayish fungal growth on the bark of the roots, and reddish, whisker-like strands between the decayed layers (ODF).

The most useful sign is often a neighbor’s tree. ODF says new hosts are infected when their roots touch old infected material, and that spread from tree to tree happens across root contacts. DecAID puts the expansion of an infection center at about 12 inches a year. A fir that went over with a small root ball last winter is a reason to have the firs within a tree length of it looked at.

Which trees are at risk and which are not

ODF ranks the hosts:

• Highly susceptible: Douglas fir, mountain hemlock, Pacific silver fir, white fir and grand fir.
• Intermediate: spruces, larch, western hemlock, and red, noble and subalpine fir.
• Tolerant: lodgepole, sugar and western white pine.
• Resistant or immune: ponderosa pine, western redcedar and incense cedar resist it; hardwoods are immune.

So a mixed yard is not evenly at risk. The bigleaf maple next to a dying fir is not going to catch it; the grand fir is. Species details are on Douglas fir and the disease itself on laminated root rot.

What a homeowner can do

There is no spray or injection. WSU’s chemical control line reads “None recommended.” What works is identification, then removal of the hazard and a change of species.

• Get a diagnosis before wind season. A certified arborist can look at the crown, the root collar and any old stumps nearby, and put the finding in writing. What that visit covers is on tree risk assessment.
• Remove infected trees near targets. WSU calls infected trees hazardous and extremely prone to wind damage. A tall fir that can reach the house is usually a sectional or crane job; see large tree removal.
• Clear a buffer of susceptible trees. WSU recommends removing susceptible hosts in a 50 ft buffer beyond the last known infected tree; ODF describes removing infected trees and buffering, then either replanting resistant or immune species or removing stumps and roots.
• Decide the stump plan. The fungus lives in stumps and large roots, and WSU says not to plant susceptible conifers where the disease is known. Grind and replant with redcedar, pine or hardwoods, or extract the roots if you want fir again; the trade-off is on stump removal vs grinding.

When the infected tree is next door

Root rot does not stop at the fence, and neither does a falling fir. In Washington, Lewis v. Krussel (2000) holds that an owner has no duty to remove a healthy tree just because wind might knock it down, absent actual or constructive knowledge of a defect; Oregon’s Taylor v. Olsen (1978) ties the duty mainly to actual knowledge of a tree’s dangerous condition. A written arborist finding about a neighbor’s fir, shared with them, changes that conversation. Cutting their tree or its roots without consent is a treble-damages risk in both states. The rules are on Washington neighbor tree law and Oregon neighbor tree law.

Sources

1. WSU Hortsense, Douglas-fir: laminated root rot, checked 2026-10-02.
2. Oregon Department of Forestry, Laminated root rot fact sheet, checked 2026-10-02.
3. USDA Forest Service, DecAID: Laminated root rot, checked 2026-10-02.
4. Washington DNR and USDA Forest Service, Forest health highlights in Washington, 2024, checked 2026-10-02.
5. Lewis v. Krussel, 101 Wn. App. 178 (2000); Taylor v. Olsen, 282 Or 343 (1978), checked 2026-10-02.
6. RCW 64.12.030; ORS 105.810, checked 2026-10-02.

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