Stretching high into the sky, previously healthy leaves and branches of an oak tree begin appearing as if death is settling upon them. That is what is occurring if the tree is infected with an especially lethal fungus. The tree is to save itself, but very little can be done.
An oak tree dies from the top down when infected with oak wilt, a fungal disease caused by the Ceratocystis fagacearum pathogen. The first symptoms appear in late spring or early summer as leaves at the top of the tree begin to turn brown and wilting. The disease progresses down the tree, causing defoliation of not only the wilted and brown leaves but of green foliage as well.
While all oak species may experience oak wilt, members of the red oak group are more susceptible than are white oaks. Oak wilt kills a red oak within one to four months. Symptoms develop more slowly in white oaks. They often survive for 1 to 7 years and may even live 20 or more years with the disease. Other disorders, like anthracnose, cause similar symptoms. However, the first signs of anthracnose are in the tree's lower section rather than the top.
Oak wilt is a fatal disease. There is no way to save an infected tree. Remove and destroy any oak suffering from oak wilt, as it spreads the contagion to other trees. One manner in which oak wilt is transmitted is via intertwined roots, known as root grafts. These grafts can occur in trees as far as 50 feet from each other. A homeowner or arborist must remove these grafts, either via chemical or mechanical means, in order to salvage the health of adjacent oaks.
Insects and animals like squirrels spread of the disease. An oak tree wounded between April 1 and July 1 is especially vulnerable to being infected with oak wilt. These wounds cause sap to ooze from the tree, drawing the attention of sap-feeding beetles that often carry the fungal disease. Immediately treat wounds with wound compound or paint.