Oak Wilt

How Oaks Become Infected?

The oak wilt fungus C. fagacearum can spread two ways, one above ground and one below ground.

Below ground Spread of Oak Wilt

Most trees can become infected by the fungus below ground. The fungus moves from an infected oak to a healthy oak via root grafts underground. The disease occurs between root systems of trees growing as far as 50 feet apart. Nearby pairs of trees may graft together in dozens of places. Most grafts occur within the same root system or between trees of the same species. But root grafts may occasionally occur between different species of oaks.

Above ground Spread of Oak Wilt

Beetles can spread Oak Wilt above ground. This is only way the disease is known to cross highways, rivers, and other physical barriers. Above ground spread occurs infrequently, but is the means by which new oak wilt infection centers can get started. Oak wilt is a lethal disease caused by a fungus called Ceratocystis fagacearum. The fungus which is commonly produced and is spread above ground beginning April 1st thru July 15th. The fungus invades and disables the water-conducting system in white, red, and other oak species creating sporulating mats (see photograph below). These mats are on red oaks that wilted during the previous summer. Sap-feeding beetles, primarily of the family Nitidulidae, are then attracted to the sweet smelling sporulating mats which lies between the bark and wood of oak wilt killed trees. The beetles feed on fungal spore mats and carry oak wilt spores to wounds on uninfected trees, continuing the spread of the disease.

Unseasoned oak firewood can spread Oak Wilt. To prevent spreading the disease, avoid moving infected firewood off site until it has been well aged. Fresh firewood must be covered and sealed to the ground with 4-mil plastic sheeting during the growing season of the year following the year in which the tree dies in order to prevent beetles from reaching the wood and picking up fungal spores. Otherwise, all infected wood should be chipped, burned, debarked, or buried prior to April 1st of the year following the year the tree dies. Because they dry quickly, wood chips from infected trees may be used in the landscape.