These oak trees are showing the symptoms of smooth patch (Figures 1, 2, 3). This condition is the result of a fungal infection that is restricted to the outer bark, causing it to slough off. The bark layer remaining is smoother and lighter in color than uninfected, normal bark. Patches can vary from a few inches to a foot or more in diameter and may occur on branches as well as the trunk. Several fungi can cause this condition. A common species, Aleurodiscus oaksii, produces clusters of flat, disc-like spore-bearing structures on the surface of the smooth bark. These structures are gray or beige in color and are usually less than 1⁄2 inch in diameter (Figure 4). The best time to see this interesting phenomenon in the forest is during wet periods in late winter before new spring growth begins, when the light gray bark stands out in the light penetrating the canopy. The fungal structures shrink when dry so will be more apparent following rainy weather.
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- Figure 1: Smooth patch symptoms beginning to merge on trunk of white oak.
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- Figure 2: Lower trunk of white oak with smooth patch symptoms.
The fungal structures may be mistaken for wood decay fungi, but because smooth patch fungi invade only the nonliving, outer bark tissues, they do not affect the health of the tree. No control measures are needed.
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- Figure 3: Isolated area of smooth patch near base of white oak.
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- Figure 4: Aleurodiscus oaksii fruiting structures on bark.
