Mold can grow on any surface that provides ample nutrients (in the form of cellulose). Wood, by its very nature, provides nutrients for mold, and is therefore susceptible to almost all varieties. If mold spores settle on an area of moist wood, you may have a serious problem on your hands. Certain mold varieties may appear white due to a lack of pigmentation.
White Mold Types
Most mold varieties frequently found inside or outside the home (with the exception of Stachybotrys chartarum, or black mold) can appear white at some stage of their development. For example, Cladosporium, which Advanced Mold Inspections recognizes as the most common household mold, can appear white, as can early stage Bipolaris (another variety frequently found in the home). Penicillium and and Aspergillus can also appear on wood as a white, patchy presence.
Powdery mildew is another white fungus entirely, but it can also appear on wood since it thrives on plant-based material. Powdery mildew has much in common with mold, such as its velvety appearance, its need for moisture and its ability to rapidly multiply its spores. Powdery mildew may appear as a white, chalky material on wood, and you may mistake it for mold. Though it grows on living plants by nature, it can spread to wood structures such as nearby fences and walls.
White Mold Dangers
Just as not all black-colored molds constitute the dreaded "black mold," not all white molds carry the same dangers. For example, Cladosporium is nontoxic, but varieties like Bipolaris, Penicillium and Aspergillus can release disease-causing mycotoxins. You cannot assess the dangers of any mold just by looking at it, and so you will need to contact a mold-removal specialist for a proper diagnosis.
Removing White Molds
For powdery mildew, apply a commercial fungicide containing neem oil. If you have powdery mildew, you should notice signs of it on leaves or plants in the surrounding area. If you cannot find any such problem, you most likely have mold. For mold, mix 1 cup bleach with 1 gallon water and spray it over the wood. Scrub after 15 minutes and rinse. Dry the wood by hand if you have no natural sunlight to remove the moisture.