Poria
Results of Fire Tests on Deck Materials

Poria -- how is it different from other decay fungi? 

Meruliporia (poria) incrassata, or "poria," as it is commonly called, is a brown-rot fungus. All decay fungi need liquid water in order to break down and utilize wood as a food source. Whereas most decay fungi must rely on a water leak, or ground contact condition, to obtain the required water, "poria" has developed a specialized root-like water-conducting tube, called a rhizomorph, (shown in the photo at right) that allows it to transport water from the soil to the wood. Therefore, even in situations where wood is protected from rainfall, and no leaks exist, wood can still be decayed by poria. Assuming you have wood infected by a brown-rot decay fungus, the best way to determine whether you have poria is to find the rhizomorphs - they will usually be in the crawlspace, along a foundation wall, or hidden behind siding in areas where it extends below the ground line, and is therefore hidden from view.

Meruliporia incrassata can be identified by the presence of the water-conducting rootlike tube (rhizomorph) and by the appearance of the fruiting body and the dark colored spores it produces. The rhizomorph looks like a barkless root and smells like a mushroom if broken open.

Poria

• Poria Stages
• Rhizo
• xactorhizo

 The composite photo above shows (clockwise from bottom right) a young fruiting body, a water-conducting rhizomorph, and a mature fruiting body.

 Finding and cutting the rhizomorphs can be difficult, particularly with slab-on-grade construction. The rhizomorphs can move through some very tight openings, such as plumbing penetrations and cold joints between two concrete pours. To prevent poria from infecting the house again, you need to change the construction detail that allowed the rhizomorph to get to the house without drying out (for example, by providing an adequate air gap between wood and soil). 

Because of the importance of finding all the rhizomorphs, homeowners should consider enlisting the help of a pest control operator with poria experience.

For more information, contact Steve.Quarles@ucop.edu

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