Oak Wilt (Ceratocystis fagcearum) is a fungal disease that clogs the vascular system of many species of oaks. The disease is spread by bark and sap beetles in the spring that feed on wounds or exposed sapwood. It is also spread through root grafts made between infected and healthy trees.
Fairly widespread through the US from the midwest down through Texas, in nearly 22 states.
All species in the Red Oak family are most susceptible.
Members of the White Oak family are more resistant.
Infected trees will begin to show branch dieback as whole branches turn brown and remain on the tree. Death can be in as little as three weeks for highly susceptible Red Oaks where some White Oaks may take years to die.
The fungus can be either transported from tree to tree through natural root grafts or through insect vectors such as bark beetles. Dead or severely dieing trees may produce a sporepad. This dark spotty structure can be located between the bark and the sapwood and produces the spores through which the fungus spreads. As it increases in size it may force cracks in the bark providing opportunities for insects to move into and out of the tree and subsequently to other trees.
Not much can be done to save an infected tree. To prevent the spread of Oak Wilt: proper sanitation of tools should also be used when pruning. Macro-injections of fungicides have been useful for protecting valuable trees nearby infected sites, lower-risk species, and as a preventative treatment. Removal of diseased trees is recommended. Root grafts made between healthy and infected trees should also be carefully excavated and severed.
As always keeping trees properly pruned, managing nutrient levels in the soil, and preventing stress are the keys to maintaining healthy Oaks in the landscape.
For a pdf copy of this factsheet: Oak Wilt