Modified woods are rapidly gaining popularity in the United States and are appearing on more public buildings. Because these are biocide-free products, they can support the growth of non-wood degrading fungi on their surfaces, many of which produce dark pigments and deface the cladding. Even growth of dark pigmented fungi on modified woods yields an even grey-black color, giving the materials a weathered look that is considered desirable by some end users. Uneven growth of dark pigmented hyphae causes patchy discoloration of the wood and diminishes the visual appeal of wooden cladding. This study describes an effort to isolate and identify defacing fungi on two buildings employing two different types of modified wood cladding in two different climates in the United States. The buildings and materials investigated were acetylated red alder on Peavy Hall in Corvallis, Oregon and thermally modified white pine on the Bell Museum in St. Paul, Minnesota. Fungal cultures were obtained from the surfaces, isolated, and identified by sequencing of the fungal Internal Transcribed Spacer (ITS) region. Several isolates of Aureobasidium and Alternaria were identified from both buildings. Microscopic analysis of fungal material on each type of wood showed hyphae and yeast cells associated with one another in an amorphous matrix of dark-pigmented material. Future investigation of the physiological characteristics of the isolated strains could provide insights into how modified woods could be improved to prevent the growth of defacing molds.

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