There are several types of fungi associated with wood, but not all of them actually cause damage.

Surface Mold and Mildew
Mold and mildew on floor joists usually indicates high moisture in the crawlspace. However, mold and mildew do not cause wood to decay. Chemical control is not needed to protect the wood, but you should take some steps to lower the moisture in the crawlspace (the same steps outlined for powderpost beetles).

Sapstain Fungi
These fungi are similar to surface molds, except that the discoloration goes deeper into the wood. The wood may have a blue, black or gray color; however, the staining fungi do not weaken the wood. Sapstain fungi indicate that the wood was wet at some time. However, once the wood dries, the fungus becomes dormant and stops growing. No chemical control measures are needed.

Brown Rot and White Rot
These fungi actually cause structural damage to wood. They often produce a white cottony growth on the surface of the wood. Brown rot is one of the most common types of wood-decaying fungi. As the wood decay, it darkens, shrinks, and twists, with cracks forming across the grain of the wood. Finally, the wood becomes dry and powdery. Wood decayed by white-rot fungi has a bleached appearance and is fibrous and soft (sponge-like). Wood that is saturated with water (30% moisture readings) will rot. If the wood moisture drops below 20%, then these fungi will not grow. Brown and white rot fungi can be controlled by removing the source of moisture that allows them to grow (e.g., by improving ventilation or drainage, repairing leaks, etc.). Spraying wood with chemicals should not be a total replacement for moisture control. If the moisture source cannot be eliminated, all decayed wood should be replaced with pressure-treated wood.

Water-Conducting Fungi
Most wood-decaying fungi only grow on moist wood and do not attack nearby dry wood. However, there are some brown-rot fungi, sometimes called "water-conducting fungi" which can conduct water for several feet through root-like strands to moisten dry wood (see picture at right). The most common type of water-conducting fungus in North Carolina is Poria incrassata (known simply as "Poria") These fungi can cause extensive damage in 2-3 years. The damage is similar in appearance to brown rot. The problem is most common in new or remodeled houses. In order to control water-conducting fungi, you must find and eliminate the source of moisture that supports fungal growth. The top priority should be to get the wood moisture content below 20%. Untreated wood in contact with or near the soil is most vulnerable. Where the fungus grows from a porch, the soil should be removed from the porch next to the foundation wall to prevent continued growth of the fungus into the house. Untreated wood should be at least 8 inches from the soil. If this is not possible, then treatment with a borate pesticide can be used.

Prepared by
Michael Waldvogel, Extension Entomology Specialist and
Larry Jahn, Extension Wood Products Specialist