Oak Trunk Green/White Growth: Lichens, Not Disease

Bark on Tree

A new Miami homeowner sees bright green/white patches on an old oak’s bark and worries about disease.

Identification

The patches are lichens—grayish-green, leafy crusts on bark. They are not pathogens; they photosynthesize independently and merely use the trunk as a substrate.

Significance

Lichens favor older trees or those with thin canopies (more light). Their presence may hint at underlying stress, but they cause none. If the oak’s canopy is full and leaves are normal, the lichens are cosmetic.

Action

• Search "lichen on tree bark" images to confirm.
• If canopy looks thin or leaves abnormal, consult a local arborist or UF/IFAS extension for a site visit.
• Otherwise, enjoy the biodiversity—lichens indicate clean air.