Updated: April 18, 2022
smooth patch on oak

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

(PDF) Smooth Patch fo Oak Trees, University of Arkansas System

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