Wood-decaying fungi are a diverse group of fungal species that feed on the structural components of moist wood, causing it to rot. They are essential for decomposition in forest ecosystems, but can also cause significant and costly damage to wooden structures in buildings. All wood-decay fungi require a certain level of moisture, typically above 20% to 30%, to grow.
Common types of wood decay:
Fungi are generally categorized by the type of decay they cause.
Brown rot: This fungus primarily breaks down the cellulose and hemicellulose in wood, leaving behind a brown, lignin-rich residue.
Appearance: As the wood dries, it shrinks and cracks against and across the grain, giving it a distinctive cubical, or brick-like, pattern. The wood becomes brittle and crumbles into a dry, brownish powder.
"Dry rot" misnomer: The term "dry rot" is often used to describe the crumbly appearance of wood damaged by brown rot, but it is misleading since moisture is required for the fungus to grow.
Examples: Common brown rot fungi include Serpula lacrymans (true dry rot) and Coniophora puteana (cellar fungus).
White rot: This fungus can break down all components of the wood, including lignin, which gives wood its rigidity.
Appearance: Affected wood takes on a bleached, whitish, or yellowish color and a soft, spongy, or stringy texture.
Effect: White rot is often more common in hardwoods than in softwoods. Some species remove lignin selectively, while others degrade all wood components at once.
Examples: Well-known white rot fungi include oyster mushrooms, tinder fungus, and artist's conk.
Soft rot: This is a less common type of decay caused by Ascomycota and Deuteromycota fungi that can thrive in conditions too hot, cold, or wet for brown or white rot.
Appearance: Soft rot attacks wood from the surface inward, creating microscopic cavities and sometimes causing a darkened, honeycomb-like appearance and cracking similar to brown rot.
Effect: While less aggressive than white or brown rot, it can still cause significant strength loss and is often found on exterior wood features.
Examples: Examples include species from the genera Chaetomium and Kretzschmaria.
Identifying wood decay fungi:
Identifying the specific fungus is often done by observing the visual signs of decay and, in some cases, the fungal body.
Rotting wood: The appearance of the decayed wood itself can help determine the type of rot present, as described above.
Fruiting bodies: The "mushroom" or conk (shelf-like growth) produced by the fungus is the reproductive stage and can be a key identifier. Some are annual, while others are perennial and add new layers each year.
Mycelium: The vegetative part of the fungus, a mass of threadlike filaments called hyphae, may also be visible as cottony growths, skin-like sheets, or root-like structures called rhizomorphs.
Managing and preventing wood decay:
Early detection and proper moisture control are critical for managing wood decay.
Remove moisture sources: The most effective preventative measure is to control moisture from leaks, high humidity, or poor drainage.
Ensure good ventilation: Proper airflow in areas like basements and crawlspaces is essential for preventing the build-up of moisture.
Professional inspection: If you suspect a serious problem, particularly in a home's structural components, a professional evaluation is recommended to assess the damage and determine the best course of action.
Common types of wood decay:
Fungi are generally categorized by the type of decay they cause.
Brown rot: This fungus primarily breaks down the cellulose and hemicellulose in wood, leaving behind a brown, lignin-rich residue.
Appearance: As the wood dries, it shrinks and cracks against and across the grain, giving it a distinctive cubical, or brick-like, pattern. The wood becomes brittle and crumbles into a dry, brownish powder.
"Dry rot" misnomer: The term "dry rot" is often used to describe the crumbly appearance of wood damaged by brown rot, but it is misleading since moisture is required for the fungus to grow.
Examples: Common brown rot fungi include Serpula lacrymans (true dry rot) and Coniophora puteana (cellar fungus).
White rot: This fungus can break down all components of the wood, including lignin, which gives wood its rigidity.
Appearance: Affected wood takes on a bleached, whitish, or yellowish color and a soft, spongy, or stringy texture.
Effect: White rot is often more common in hardwoods than in softwoods. Some species remove lignin selectively, while others degrade all wood components at once.
Examples: Well-known white rot fungi include oyster mushrooms, tinder fungus, and artist's conk.
Soft rot: This is a less common type of decay caused by Ascomycota and Deuteromycota fungi that can thrive in conditions too hot, cold, or wet for brown or white rot.
Appearance: Soft rot attacks wood from the surface inward, creating microscopic cavities and sometimes causing a darkened, honeycomb-like appearance and cracking similar to brown rot.
Effect: While less aggressive than white or brown rot, it can still cause significant strength loss and is often found on exterior wood features.
Examples: Examples include species from the genera Chaetomium and Kretzschmaria.
Identifying wood decay fungi:
Identifying the specific fungus is often done by observing the visual signs of decay and, in some cases, the fungal body.
Rotting wood: The appearance of the decayed wood itself can help determine the type of rot present, as described above.
Fruiting bodies: The "mushroom" or conk (shelf-like growth) produced by the fungus is the reproductive stage and can be a key identifier. Some are annual, while others are perennial and add new layers each year.
Mycelium: The vegetative part of the fungus, a mass of threadlike filaments called hyphae, may also be visible as cottony growths, skin-like sheets, or root-like structures called rhizomorphs.
Managing and preventing wood decay:
Early detection and proper moisture control are critical for managing wood decay.
Remove moisture sources: The most effective preventative measure is to control moisture from leaks, high humidity, or poor drainage.
Ensure good ventilation: Proper airflow in areas like basements and crawlspaces is essential for preventing the build-up of moisture.
Professional inspection: If you suspect a serious problem, particularly in a home's structural components, a professional evaluation is recommended to assess the damage and determine the best course of action.
