Poria: The House
the last 2 decades Meruliporia incrassata, sp., an orange colored mushroom
shaped macro fungus, with the appearance of pancake batter, has shown up
recently in homes from San Diego to northern California. However, poria
incrassata, the water-conducting fungus occurs mainly in the southern
states, it can be found anywhere. In the past, reports of poria was
confined mainly to the Gulf states Miss., Al., Tx., etc.
"It's a rare fungus, but it's as common here as anywhere in the world,"
said UC Riverside plant pathology professor John Menge. "Poria is the most
devastating wood-decaying fungus of houses that we know of."
Poria is one of many wood decay fungi that feeds on dead wood. It sounds
like science fiction and looks like it too, but poria, like all decay
fungi, is an organism that needs moisture to break down and utilize wood
as a food source, according to forest product experts at UC Berkeley. But
unlike other wood-decaying fungi, which tend to destroy only a six inch
area around a plumbing leak or wet window sill, poria has the capacity to
begin in wet soil as opposed to just damp soil.
Experts say this water-conducting fungi differs from most other wood decay
fungi in several respects: Large, semi-tough water-conducting roots called
rhizomorphs are formed which transport water by capillary action from a
constant source (usually damp or wet soil) to dry wood in a building,
wetting it sufficiently to support decay. As decay proceeds, water is
conducted to dry wood adjacent to that already colonized fungi. In this
manner, as long as the supply of water is available, water-conducting
fungi can colonize and decay the wood to the entire structure. "In other
words, because fungus does not have teeth to help it eat, it has to spit
on the wood. And the enzyme it secretes turns the wood to mush. Any piece
of wood exposed to this fungus is destroyed" says poria expert Glenn
We used to think poria would usually start under a newly installed patio,
with new landscaping or with a new room addition, and can travel far from
its original water source. But that is not always the case. Wayne Wilcox,
a UC Berkeley forestry professor, has found a similarity among houses with
poria and the fact that major landscaping was done within 2 years of
poria's onset. He speculates that the soil dumped on these suburban lawns
originated in various forests around the world, where poria occurs
naturally and helps in the process of decomposition, and he feels poria
may have come along for the ride.
Donna Kingwell, a spokeswoman for the California state's Structural Pest
Control Board, said "the agency is keenly aware of the potent problems of
poria, especially in the southern part of California".
First reports of poria incrassata destruction surfaced in 1913 in the
southeastern United States, where forest products were the suspected
origin of the fungus-abound. There is no record of the first reported case
of poria in California, according to Wayne Wilcox, a UC Berkeley forestry
professor, but scientists discovered the telltale spores on three coastal
redwoods in 1924. Infestations of poria are rare. Only 15 cases were
reported state wide by 1968, according to a U.S. Department of Agriculture
"When poria does invade a house, it's almost always catastrophic", said
Mississippi State University wood technology professor Terry Amburgey.
"The fungus will infiltrate a foundation, wood or concrete, and pretty
soon the entire house goes".
Poria has an appetite not only for common construction woods such as oak
and pine, but for cedar, redwood, cypress and juniper that are naturally
decay-resistant. In addition to attacking most woods classed as naturally
decay resistant, laboratory tests show that poria is resistant to many
fungicides containing copper. The practical significance of this tolerance
is uncertain, but no failures of wood treated with copper fungicides have
been reported in buildings to date.
When poria attacks a building, spectacular damage often results once well
established it can destroy large areas of floors and walls every year or
so. Fortunately, control is relatively simple, i.e. the permanent
elimination of the water source. Although poria is relatively rare, the
rapid and extensive damage it can cause makes it desirable to understand
the conditions leading to the attract, the signs indicating an attack is
in progress, and methods of prevention and control of an attack.
Picture Jan. 17, 2011, of poria growing in a southern California home.
Taylor, Certified Mold Inspector.
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