Laminated Root Rot is Zombie Apocalypse Equivalent in the Forest

Fruiting bodies of Phellinus weirii that cause Laminated root rot

Fruiting bodies of Phellinus weirii that cause Laminated root rot

Did you hear the one about the fungi that took up residence in the forest? Turns out he wasn’t such a “fun guy”. He infested an entire grove of Douglas Fir trees with Laminated Root Rot.

Sorry. Bad joke.

All kidding aside, Laminated Root Rot is a serious threat to conifers here in Portland and much of Northwest Oregon. It is classified as a fungal pathogen that causes damage to the root systems of fir and cedar trees. Infection is primarily spread from tree-to-tree via the network of roots below the surface. However, it can continue to live on in the host stump for years. Seedlings that come into contact with the infected wood are at risk of contracting the pathogen.

As the fungus grows, the roots begin to decay. This prevents critical absorption of water and nutrients needed for survival. Infected trees begin to weaken and ultimately meet their untimely death. Laminated Root Rot is the most aggressive, and destructive, fungal pathogen responsible for the death of Douglas Firs in the Pacific Northwest.  It has been cited as the cause of millions of acres of tree loss. Consider it the zombie apocalypse equivalent in the forest.

Diagnosing Laminated Root Rot

Common signs to watch for include trees that appear to have had a “stumped” growth. They are smaller and lack vigor compared to neighboring healthy trees. The crowns typically will yellow and become thin. As decaying of the roots progresses, the wood becomes softer and the production of cones begins to dwindle.

In affected areas, it is common to find multiple, seemingly healthy green trees that have been blown over. This phenomenon is the result of what experts describe as “wind thrown.” The wind literally knocks the trees over because they have become unstable without the support of the root system to hold them in place.

If you suspect that your trees are suffering from Laminated Root Rot, you have a few options to help restore the health of your grove.

  • Consider thinning trees to prevent root-to-root contact and the spread of the fungus.
  • Remove any infected remains including the stumps.
  • Avoid planting trees that are known to be susceptible and instead, replace with a resistant species.

Don’t let an unwanted, not-so-fun fungi destroy the health of your trees. If you’re unsure about how to diagnose your ailing trees or need to create a plan to remedy the situation, a trusted certified arborist is going to be the best bet in offering the guidance you need.

Photo By USDA Forest Service Archive [CC BY 3.0 (], via Wikimedia Commons

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