How To Spot Laminated Root Rot & Phytophthora Root Rot

Serving Families Throughout Portland & the Pacific Northwest

Our mild climate is perfect for growing but unfortunately, that also includes pests and diseases.  Laminated Root Rot and Phytophthora Root Rot are two common diseases that may affect trees on your Portland, Salem or SW Washington property.

To help protect your trees and shrubs, here’s the signs to look for as well as how it spreads.  Keep in mind that if one of your trees becomes infected, it can be passed to surrounding trees.  Remember, treatment is most effective when administered early.

Laminated Root Rot

While it affects all conifer species, Douglas fir, Mountain hemlock, white fir and grand fir are the most susceptible.  In fact, laminated root rot is the most destructive root decay of Douglas firs in the Pacific NW.


Trees that have been blown over in high winds often reveal decayed roots that are stubbed off.  Affected standing trees may have foliage in the crown that is thin and have turned yellow or yellowish-white in color.  They may also produce an abnormally heavy crop of cones.

Crown symptoms are usually not seen until at least half of the root system is affected. Decayed wood separates easily (or delaminates) at the annual rings with pitting evident in the wood.  Reddish brown whiskers of the fungus called setal hyphae may be found in the infected tissue.


The fungus is spread by root to root contact, which means it can be spread to nearby trees.  Through the fungus does not grow through the soil, it can survive up to 50 years in roots and stumps of dead trees.  During that time, it can infect any trees that come into contact with the infected wood.

Phytophthora Root Rot

Many popular ornamental trees and shrubs in our area are prone to Phytophthora root rot.  Trees that are particularly vulnerable are oak and dogwoods.  Please note that keeping the soil around the base of the plant wet for long periods of time can invite root and crown rot.


Classic signs of a root disease are easily spotted.  The first thing you’ll probably notice is leaves appear drought-stressed and often die quickly when the weather warms in late spring or early summer.

  • Leaves appear drought stressed.
  • Leaves may turn dull green, yellow, red, or purple as they wilt.
  • Bark around the soil line may darken.
  • Cutting away bark reveals red-brown discoloration in the wood.

Infected trees may survive several years before killing the whole plant.  Signs of Phytophthora root rot is different than Armillaria root rot in that mycelial mats do not develop in tissues infected with Phytophthora root rot.

FYI-mycelial mats associated with Armillaria root rot are white, creamy paper thick fan-shaped sheets of fungus strands that grow between the bark and wood. Learn more by reading our Armillaria root rot post.


The key to saving trees and shrubs is catching any disease or infestation early so contact us when you first see signs that a tree, shrub, or plant is unhealthy.

The post How To Spot Laminated Root Rot & Phytophthora Root Rot appeared first on General Tree Service.

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