Smooth patch is a
condition in which the outer, rough bark of a tree falls off in
patches, leaving smooth, somewhat depressed areas. This condition,
caused by the fungus Aleurodiscus oaksii, causes smooth
patch on a number of hardwoods and conifers. However, in our area
smooth patch is most commonly seen on white oak.
The fungus colonizes
the dead outer layers of bark on living trees causing the bark to
slough off. The smooth, light colored depression is usually
irregular in shape and size, ranging from a few inches to more
than a foot across. Since the fungus does not invade living
tissue, smooth patch is not harmful to the tree.
structures of the fungus, also called fruiting bodies, are
sometimes noticeable in wet weather. They are usually small, 1/8"
or 1/4" in diameter. The structures form flat, leathery discs,
cream-colored to light gray or beige, and curled at the edges.
They grow in clusters on the affected bark and are sometimes
described as looking like lichens. In dry weather, the fruiting
bodies shrivel up and become inconspicuous. Fruiting bodies may
persist on the tree all year.
P439S Revised 2/99
Chad Behrendt, Crystal Floyd - University of Minnesota,
Extension Service - Judy Hubbard, Cynthia Ash
Smooth Patch on Bark
Have you ever noticed a
smooth, light patch on the bark of a tree? Certain saprophytic
(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
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.
Department of Plant Pathology,
Iowa State University,
Photo: Chad Behrendt
by: Department of Plant Pathology
The outer bark falls off in patches, leaving smooth,
Photo: Robert L. Anderson USDA Forest Service light colored depressed areas on the trunk.
wintering: In plant material
Infection: Growing season
dispersal: Wind and rain Smooth
patch often forms small white, disk-like fruiting structures
point: Bark of Tree on
Properly water, fertilise, and mulch trees
Smooth patch is most commonly seen on white
click on a photo
below to enlarge
University of Minnesota, Yard and Garden Clinic
Developed (1999) and maintained by
Chad J. Behrendt, Ph.D. and Crystal M. Floyd