Laminated root rot also known as yellowing ring rot is caused by a fungal pathogen Phellinus weirii

Phellinus weirii

Phellinus weirii is a plant pathogen causing laminated root rot in certain conifers, typically Douglas-fir and western redcedar. It is widespread in the Douglas Fir Growing regions of British Columbia, Washington and Oregon.-Overview:...

(poria). Laminated root rot is one of the most damaging root disease amongst conifers in northwestern America and affects mostly fir trees

Fir

Firs are a genus of 48–55 species of evergreen conifers in the family Pinaceae. They are found through much of North and Central America, Europe, Asia, and North Africa, occurring in mountains over most of the range...

 and cedars

Thuja plicata

Thuja plicata, commonly called Western or pacific red cedar, giant or western arborvitae, giant cedar, or shinglewood, is a species of Thuja, an evergreen coniferous tree in the cypress family Cupressaceae native to western North America...

.. Douglas fir, mountain hemlock, Western Hemlock grand and pacific silver fir are highly susceptible to infection with Weirii. A few strains of plants such as western white pine and Lodgepole are tolerant to pathogen while ponderosa pine is resistant to it. Only hardwoods are known to be immune to the pathogen and therefore are not infected with yellow ring rot.

Symptoms and Signs

Laminated root rot mainly attacks Douglas fir, Mountain Hemlock, Western Hemlock, Grand and Pacific fir. The disease infects trees between 6 years and their year of rotation Diagnostic symptoms include crown yellowing and thinning, distress of cones, red brown stained outer heartwood, annual rings separate. Also plants infected with laminated root rot are usually in patches or groups since the disease is spread within a short range. Infected or decayed roots break close to the root forming “root balls.” Laminated root rot is frequently detected during ground surveying when canopy openings and standing dead and fallen trees are observed.
Signs of Laminated root rot can are the red fungal hairs between sheets of decomposing wood and also the buff colored mycelia on the outside of the roots.

Discovery

The fungus Phellinus weirii was first discovered in 1914, on western redcedar in Idaho

Idaho

Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

. The first reported instance in Douglas-fir

Douglas-fir

Douglas-fir is one of the English common names for evergreen coniferous trees of the genus Pseudotsuga in the family Pinaceae. Other common names include Douglas tree, and Oregon pine. There are five species, two in western North America, one in Mexico, and two in eastern Asia...

 was in 1940, in Cowichan Lake, British Columbia

British Columbia

British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

.

Disease Cycle

There are two types of the Phellinus; one that causes laminated root rot in Douglas fir, Hemlock and grand fir and the the other that causes butt rot in Western Red Cedar. The Mycelium of this fungus doesn’t grow in the soil and also its spores are not spread by wind like most fungal pathogens. Infection occurs when roots of healthy trees grow in contact with infected roots. After initial contact with a living root, the mycelium grows on the bark, extending only a few millimeters into the surrounding soil. Mycelium penetrates the host through injured bark and advances proximally and distally along newly infected roots. It eventually penetrates through the host’s cambium and grows inside the wood causing decay and death of living cells in the heartwood and sapwood. Phellinus poria over-winters within infected stumps and can remain viable for up to 50 years

Spread

Phellinus weirii spreads by root contact, and then infects and kills the host. After killing the host, it then colonizes the host to use it as a food source. P. weirii is also known to infect bark

Bark

Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner...

, but this infection process is not well understood. Older trees are more resilient to infection, although trees of all age may be infected.

Management

In all cases of the disease, thorough study of the distribution and intensity should be determined to help choose a management practice that’s cost effective. For example, if the disease is widespread in a pre-commercial stand, destroying the plantation may be the most effective measure. The area can then be replanted with immune or low-susceptible species. Aerial surveying is a viable tool available for use in areas where there are severely damaged systems.

• Using up to date models to help predict the spread of the disease can help with management choice
• Susceptible species should not be planted within 100 feet of a disease center
• Remove as many infected roots and stumps as possible to avoid inoculation of healthy plants
• Cut all infected trees within the disease center and all uninfected trees within 50 ft of the disease center
• Stumping is an expensive, yet effective measure in gently sloping, high-quality sites with light soils. After an excavator removes the stump, pieces of the root are torn and fragmented so invading soil organisms deter long-term inocula.
• Push-falling is an alternative to post-harvest stumping. Whole trees are pushed over with machinery to expose diseased roots for removal. Push-falling is effective in areas with slopes less than 30 percent and soil textures that are sandy to sandy loam.
• Applications of chemical fumigation (such as chloropicrin) have been unsuccessful in dealing with Laminated root rot.

Importance

Laminated root rot is a serious disease that infects trees between 6 years and the year of rotation. The trees die from failure to take up water and nutrients because of the main roots are decayed. The death is also accelerated by wind that throws the trees down. It is estimated that Laminated root rot reduces timber production by about 4.4 million cubic meters annually.Wood losses in British Columbia are estimated to be 1.4 million cubic meters.