By Kathy Luedke, HOA Board Member
Oak Wilt Identification
Foliar symptoms, patterns of tree mortality, and the presence of fungal mats can be used as indicators of oak wilt. However, laboratory isolation of the fungus is recommended to confirm the diagnosis. A trained expert should be consulted when in doubt.
Patterns of Tree Mortality
Most live oaks defoliate and die within 3 to 6 months following initial appearance of symptoms. Some live oaks take longer to die, and a few untreated trees may survive many years in various stages of decline. Occasionally, a few live oaks in an oak wilt center may escape infection and remain unaffected by the disease.
Many infected white oaks will exhibit some canopy loss and generally the disease will not spread to adjacent trees. Lacey oaks, white shin oaks, and chinquapin oaks sometimes form root connections similar to live oaks, offering a pathway for the disease to spread to adjacent trees, causing higher infection and mortality rates than in other white oak species.
Red oaks never survive oak wilt and often die within 4 to 6 weeks following the initial appearance of symptoms. During summer months, diseased red oaks can often be spotted from a distance because of their bright, autumn-like coloration in contrast to the surrounding greenery. This symptom is called flagging.
Foliar (Leaf) Symptoms on Live OaksLeaves on diseased live oaks often develop chlorotic (yellow) veins that eventually turn necrotic (brown), a symptom called veinal necrosis. This is the most commonly seen foliar symptom on live oaks that are infected with oak wilt. Another symptom that leaves can exhibit is vein banding, where the leaf vein is a darker green than the rest of the leaf. Tip burn or margin burn, which turns the edges of the leaf brown, can also be seen on leaves. Defoliation may be rapid, and dead leaves with brown veins often can be found under the tree for months after defoliation.