What to do when wood-destroying fungus invades your house



Q: We had a large liquid amber tree removed from our front yard in Santa Cruz, Calif., about three years ago after the roots invaded the sewer line and raised the concrete driveway. The stump was ground and has been decaying.

However, after the first rains of the season, I noted that, within the space of several days, a white fungus had crept out at a rate of at least a foot a day, and the mycelium spread throughout the surrounding soil. It is about 10 feet from the foundation. We have tentatively identified it as Poria incrassata. Is my house in danger? Will it affect live plantings? Are wood planter boxes at risk?

A: If it is the fungus long known as Poria incrassata but now officially called Meruliporia incrassata, you’re smart to be concerned. Often called the house-eating fungus, it’s considered one of the most devastating of all the fungi that destroy wood. Given that fungi cause more damage to structures than termites and other insects, that ranking is pretty scary. Long found mostly in the Gulf states, it’s now showing up along the West Coast, but it’s still rare enough there that many structural pest-control experts have never seen it.

This fungus is one of many “brown rot” fungi, because it digests the sugary cellulose in wood but not its lignin. Lignin is brown, so the weakened wood still has that color. (White-rot fungi digest both cellulose and lignin but leave some cellulose, which is light-colored.) But unlike other brown-rot or even white-rot fungi, the house-eating fungus doesn’t just destroy wood that’s damp because of plumbing leaks or contact with soil. This fungus also sends out rootlike structures called rhizomorphs that bring water to wood that would otherwise be dry, thus making the wood damp enough for the fungus to digest. The rhizomorphs can extend into new wood by several inches a day, a remarkable speed.

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In nature, this fungus serves a useful purpose by helping to break down dead wood and dead roots. It can attack living trees — one study found it in redwoods — but it usually spreads to home environments through trucked-in soil that contains compost made from infected wood. The remnants of the tree you removed might have become infected that way.

If it is just in the soil away from your house and there is no way for the rhizomorphs to worm their way into your home, and if you don’t have a water source nearby, such as sprinklers that cause water to puddle next to the foundation, then the planter boxes might succumb, but your house might be safe. It would definitely be wise to have a pest-control expert — one who focuses on structural pests such as termites, rather than mold remediation — carefully inspect the area.

If your house has an elevated foundation with a crawl space, that would be one place to check for the rhizomorphs, which look like tan or black roots but lack bark. When broken open, they smell like mushrooms. They can be quite narrow, fitting through cracks in a foundation, but are more likely to be pencil-thick or even thicker. The University of California’s Cooperative Extension service provides an excellent primer with photographs of the rhizomorphs and other evidence of the fungus, as well as diagrams showing how it got into several homes.

If the fungus has gotten into your house, the only effective treatment is to dry out the wet wood, remove and replace what the fungus reached, and remove all contact with the water source. Fungicides aren’t effective at killing this fungus.

Jehremy Foster, chief estimator for Precision Environmental (precisionenv.com), which treats for this fungus and offers a range of other remediation services in Southern California, said the treatment protocol might seem simple, but actually doing it can be very time-consuming — and expensive.

“You need to remove all signs of the fungus — anything it’s touched,” he said, explaining that this precaution will remove spores that could start a new infestation if a leak were to occur in the future. “So there’s a lot of demolition. A lot of the wood is fairly destroyed. Then you need to track down the rhizomorphs, the roots that are pulling in the water, usually from the soil.” Investigators usually start inside, opening up walls and floors as needed, and work backward to where the fungus got into the house.

“Outside, it’s sort of like an archaeological dig,” Foster said. “We have to be careful as we remove soil, so we don’t lose track of where it’s growing.” Sometimes there’s a single water source and a “primary root ball” with a big bundle of rhizomorphs. But finding one water source or that root ball can be misleading; a rhizomorph may continue on to a second moisture source.

The treatment cost varies considerably, depending on the situation. Sometimes, the work has to include fixing construction defects that made the house vulnerable, such as direct contact of wood to soil or to damp masonry, or relandscaping to keep water from pooling alongside the house.

Foster said his company always charges for time and materials, rather than bidding a specific amount. In recent months, one job cost only $3,000. But then there was the five-story beach house in Marina del Rey where the fungus had reached up a staircase to the top floor. Tracing that and removing the damaged wood cost $50,000 — and that was before the owners paid to build new stairs.

Have a problem in your home? Send questions to localliving@washpost.com. Put “How To” in the subject line, tell us where you live and try to include a photo.