University of Maryland Extension

Smooth Patch on Oak

smooth patch disease
Smooth patch on lower trunk of a white oak tree

Key Points

  • Smooth patch goes by other common names including white patch or bark patch.
  • The most commonly affected oaks in Maryland are white oak, Q. alba, and post oak, Q. stellata.
  • Smooth patch can be found on oaks in both urban and forested areas. White patch symptoms on trunks are commonly seen and are often used in a forest setting for identifying white oaks from other oak species. 
  • Symptoms are often noticed when looking for reasons why a white oak tree is declining in the landscape.

Symptoms and Causes of Smooth Patch

  • The main symptom is sunken white-colored areas on trunk bark. 
  • The smooth patch fungus produces clusters of flattened cup­like spore-bearing structures on the bark surface.
  • These structures are light gray or beige in color, are usually less than 1/2 inch in diameter, and are usually curled at the edges.
  • Exfoliation of the bark results in smooth, grayish patches adjacent to the normally rough bark.
  • It is caused by a superficial colonizing fungus, Aleurodiscus oakesii.
  • Since the fungus invades only the nonliving, outer bark tissues, this colonization is not harmful to the tree and has no long-term affects on tree health.


  • Treatment is not necessary. 
  • Deeply water trees during drought and avoid wounding the trunk and branches of trees.

Additional Resource

Author, Dr. David L. Clement, Extension Specialist, Plant Pathology



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