Hypoxylon canker is a fungal condition that shows up on oaks and several other hardwood species throughout Florida. It is important to understand that this fungus is almost always a secondary problem, not the original cause of a tree's decline.
What to look for
The most recognizable sign is a pale, silvery, or tan patch on the trunk or a major limb where the outer bark has died and sloughed away. Underneath, the wood often has a distinctive stromata, a fungal structure that can vary in color and texture as it matures. By the time this is visible on the outside of the tree, the fungus has typically been growing within the wood for some time.
Why it shows up
Hypoxylon fungus is present in the environment and in the wood of many healthy trees without causing visible problems. It becomes active and destructive when a tree is already weakened by another stressor, such as drought, root damage, soil compaction, storm damage, or old age. In other words, the appearance of hypoxylon canker is usually a signal that something else has already put the tree under significant stress.
Why the whole tree matters
Because hypoxylon is secondary, evaluating just the canker is not enough. A certified arborist needs to assess the overall condition of the tree, including the extent of the internal decay, the tree's structural stability, and what originally stressed the tree, to determine whether it is a safety risk and whether any part of it can be saved.
What to do
An oak showing this kind of bark loss, especially one near a home or other structure, should be evaluated promptly. ArborManagers provides tree health assessments and tree risk assessments throughout Central Florida. Call us at (352) 414-2454 or request a consultation online.