Laminated Root Rot: Invisible and Devastating

Michael French

Laminated Root Rot (LRR), caused by the fungus, Coniferiporia sulphurascens (formerly Phellinus weirii), is widespread across Anderson Island. It is responsible for a large share of the trees that are blown over. There is no easy fix for our LRR problem. Douglas fir trees are highly susceptible to LRR, and Douglas fir is the dominant tree on our island.

In commercial operations, LRR is countered by cutting down all obviously infected trees and those immediately proximate to them, then pulling them and turning the stumps upside down. A tree species that is known to be resistant to LRR is then planted. This remedy is not a good option for our island because LRR is so widespread that few trees would remain, not to mention the cost of pulling and turning roots. Our landscape would look post-apocalyptic if we undertook this remedy. Additionally, resistant species are just that, resistant, and not impervious. The amount of LRR that would remain in the roots left behind in the soil would continue to represent a large volume of infected material, active for several decades.

Fortunately, or unfortunately, much is known about  LRR because it is one of the most ecologically and economically devastating root diseases affecting conifers in northwestern North America. In commercial timber stands, it is particularly notorious for its ability to persist in the soil for decades, acting as a “permanent resident” that gradually expands across forest stands.

Understanding Laminated Root Rot

The disease is a wood-decaying fungus that spreads almost exclusively through root-to-root contact. When the roots of a healthy tree touch those of an infected neighbor or a colonized stump, the fungus migrates across the contact point. It then invades the root’s inner tissues, destroying the tree’s ability to transport water and nutrients. The pathogen is remarkably resilient, surviving in large stumps and root systems for 50 to 100 years even after the host tree has died or been harvested.

How to Identify the Disease

Identification can be difficult because symptoms often remain hidden until more than 50% of the root system is destroyed.    

Crown Symptoms

Early indicators include reduced terminal growth and thinning foliage. In later stages, the crown may turn yellow (chlorosis), and the tree may produce “distress crops” of small cones.

Root and Wood Signs

• Lamination: The most definitive sign is wood that separates easily along its annual growth rings, looking like pages in a book.

• Pitting: Both sides of these separated sheets typically show tiny, oval pits about 0.5–1 mm long.

• Setal Hyphae: Using a hand lens, you can often see “reddish whiskers”—tiny, hair-like fungal structures called setal hyphae—between the wood layers.

Root Balls

Remedies and Management

There is no chemical “cure” for a tree once it is infected, so management focuses on containing the spread and rehabilitating the site.     

• Buffer Zones: To stop the underground spread, foresters often remove all infected trees plus a 50- to 100-foot buffer of healthy-looking trees around the infection center.
• Stump Removal: On productive sites, mechanical stump and root excavation is used to physically remove the inoculum from the soil.
• Species Conversion: The most practical long-term remedy is to replant infected areas with resistant or immune species.
  • Immune: All hardwoods (e.g., Red Alder, Bigleaf Maple).
  • Resistant: Western Red Cedar and Ponderosa Pine.
• Long-term Fallow: Leaving a site free of susceptible conifer hosts for at least 50 years allows the fungus to naturally die out as its food source decays. 

The sheer amount of LRR on our island is a consequence of the island’s history. Most of the Douglas fir timber on our island was logged off over a relatively short span. Douglas fir seedlings spring up like mad in an open, logged-off area. These rapidly growing seedlings were not managed. They weren’t thinned out when they were young trees, nor were they selectively harvested as they rose to maturity. LRR spreads from the infected roots of one tree, intermingling with the roots of another tree, and the environment created of dense thickets of Douglas fir seedlings ensured widespread transfer of this disease. Once the connections of root to root contact is made no, after the fact, thinning or selective cutting operation will impact the disease.

We are not without options for our woodlands. While traditional remedies are largely ill-suited for our island, that doesn’t mean we are unable to do anything. Natural succession is occurring at this moment. The oldest areas of infection, where old snags have crumbled and fallen, or blowdown has decayed to nearly duff, are currently filled with hardwoods (alder, bigleaf maple, willow, etc.). Some of these hardwood zones are already aging, and it’s time to think about what comes next for these areas.

In short, we have a widespread LRR problem across our island. There are no easy solutions, but there are some opportunities to guide and manage our woodlands to a healthier future.

Do you see or have evidence of LRR on Island Property? What to learn more? Reply to this post or contact us directly.