It's amazing to me how something as small as a fungus can take down something as majestic as an Oak tree. But it sure can. In a short 4-6 weeks, a once beautiful Red Oak will be killed by Ceratocystis fagacearum. Oak trees within the Red Oak family are more susceptible to the disease than White Oaks, but White Oaks aren't immune.
AND the disease can easily spread between trees, so at the first sign of Oak Wilt, you want to call in a tree care expert to determine if you need to cut down the tree or if it can be saved. It's bad enough to lose one tree, but even worse to lose all of them! If the tree cannot be saved, the roots will need to be severed between the diseased tree and other trees. Cutting down the tree before "vibratory plowing" is known to cause the disease to spread more quickly.
Oak Wilt disease is spread both above ground and under ground.
Above ground the disease spreads when when a nitidulid beetle feeds on the fungal mat of an infected oak and then lands on a fresh wound of a healthy oak. This is one of the reasons it's important to prune oak trees in the winter. The beetles aren't active in winter so the wounds caused by pruning heal before the beetles are mobile. The beetles are most known for transporting Oak Wilt between April and July, so definitely stay away from that time frame with regards to pruning oak trees.
Below ground oak tree roots graft together. It isn't uncommon for different species of oak trees to graft together either. When the roots of an infected Oak graft with the roots of a healthy Oak, the oak wilt disease travels through the grafted roots from the sickly tree to the healthy one. This can happen between trees as far apart as 50-80 feet.
Where did Oak Wilt start?
No one really knows where the disease started. However, according to the U.S Department of Agriculture Forest Service,
It was first recognized as an important disease in 1944 in Wisconsin (fig. 1) where, in localized areas (less than 100 acres (40.4 ha)), over half the oaks have been killed. Surveys in eight Wisconsin counties showed that about 11 percent of the annual growth increase of oak forests was offset by mortality caused by oak wilt."
Since 1944, the disease has spread south and east, affecting Oak trees in 23 known states.