Smooth Patch on Bark

Have you ever noticed a smooth, light patch on the bark of a tree? Certain saprophytic fungi (those that live on dead organic matter) decompose the rough, dead outer bark of trees. This results in smooth grayish patches that are adjacent to the normal, rough bark. Small patches may expand slowly over time, coalescing to form smooth grayish areas that are several feet in length. Aleurodiscus oakesii is one of the fungal species that can cause smooth patch and may occur on trees such as American elm, sugar maple, and various oaks.

Some of these fungi produce whitish fruiting structures that are visible on the bark, which sometimes causes them to be mistaken for serious wood decay fungi. These smooth patch fungi, however, do not cause cankers or internal decay. They cause no known harm to the tree.

Smooth patch is also referred to as white patch or bark patch.

This article originally appeared in the January 15, 1999 issue, p. 1.

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