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More wood is destroyed each year by decay than by all the fires, floods, and termites combined! Commonly called rot, wood destroying fungi need three things to survive, air, water, and food. Since we can't eliminate air and their food is the wood in our homes, the only mechanical control mechanism available to us is the elimination of water. Water is the enemy of wood! Although we've all heard the term "dry rot," dry wood will not rot!
The types of wood destroying fungi encountered by pest management professionals and homeowners fall into two basic categories: brown rot and white rot. White rot attacks the cellulose and lignin in the wood giving the wood an off-white appearance. In the later stages the wood becomes spongy to the touch. White rot typically attacks hardwoods and lacks the cubical checking appearance of brown-rotted wood.
Brown rot commonly attacks softwoods turning the wood dark brown. In advanced stages of decay, wood attacked by brown rot becomes friable and splits appear across the grain giving the wood a "checkerboard" appearance. Infested wood may be structurally weakened in a relatively short period of time. Once brown rot has extracted all of the nutrients from the wood the wood may become dry and powdery. This leaves the impression that dry wood has rotted (dry rot) but in reality it is an old infestation of brown rot.
One of the most destructive types of brown rot fungi is poria incrassata, otherwise know as the water-conducting fungus. This type of fungus actually transports water through root-like structures known as rhizomorphs. Infestations of poria incrassata can progress quite rapidly destroying portions of flooring and wood members in a year or two. One indication of a poria incrassata infestation is the presence of rot in wood with no visible source of water. A moisture meter is the best tool is determining the extent of an infestation. Any wood having a moisture content in excess of 40% without an apparent source of water may well be infected with poria incrassata.
Many people confuse the presence of molds with decay fungi. Although molds are a form of fungi, they typically grow on the surface of wood and generally do not weaken the wood's strength. However, the presence of mold is a good indication that the moisture level in the wood is high enough to also support the growth of decay fungi. Moisture control methods used to prevent decay fungi will also remove conditions favorable for mold growth.
Elimination and Prevention of Decay Fungi
Some type of moisture control should be an integral part of any program designed for the elimination of decay fungi. The following rules are a good place to start:
- No wood should ever be in contact with the ground. Wood posts, piers, supports, etc. should always rest on concrete footers raised above the level of the surrounding soil.
- Basements should be waterproof and equipped with a floor drain. If the relative humidity in the basement exceeds 50%, a dehumidifier should be installed.
- Crawlspaces should be adequately ventilated with at least one square foot of free vent area for every 500 square feet of crawl space floor area along with a moisture barrier covering at least 80% of floor. One vent should be placed within three feet of each corner to prevent "dead air" spaces and in high humidity environments additional vents should be considered.
- Plumbing leaks should be repaired as soon as they are noticed.
- Rain gutters need to be clear of debris and roof leaks fixed.
- Exterior wood should be coated with a water repellent paint or stain.
Chemical Control Methods
Both Armor-Guard® and Shell-Guard® are labeled for treating wood for decay fungi including brown and white rot. Most decay fungi are quite sensitive to borates, so for most situations Armor-Guard will suffice for treating an area. However, if there are fruiting bodies present or hair-like growth on the surface, Shell-Guard should be used to treat these heavily infested zones.
If you are working in a crawl space, be sure to remove any insulation that may be present between the floor joists before you begin and check the entire area with a moisture meter. If there are any sections of wood where the moisture content is 20% or above, a preventative treatment with Armor-Guard is recommended. Follow the label directions and spray the wood to the point of run-off. After treatment, make sure all crawl space vents are open and, if necessary, install temporary fans to help dry the wood before replacing the insulation. We also recommend that moisture control be incorporated into any program involving infestations related to high moisture conditions.
Within a few days after a treatment has been completed the fungi will begin to die and dry up. Occasionally the dead fungi will emit an unpleasant odor as it decomposes. This odor will only last a couple of days and may be minimized with the circulation of fresh air into the treated area.