Tree Diseases 101: Oak Wilt

Oaks are among the most beloved of American shade trees. Unfortunately, more and more oaks are succumbing to the debilitating disease known as oak wilt. To ensure that the oak trees on your property remain healthy and happy, it is important that you learn as much as you can about this disease. This article will arm you with valuable information about how oak wilt spreads, and how you can recognize it.

Basic Information

Oka wilt is caused by a fungus with the scientific name of Ceratocystis fagacearum. This non-native species does not affect oak trees across the entire country. Rather its ill effects are concentrated across twenty-four states, most of which are located in the Midwest, with Minnesota, Iowa, and Illinois being among the most affected states. That said, oak wilt continues to spread across the country at an alarming rate.

How Oak Wilt Spreads

Oak wilt is transmitted in two main ways. The first is through insect infestation by a species of beetle known as sap beetles. These beetles tend to be attracted by certain volatile chemicals produced by the spore mats of trees that have been killed by oak wilt. The beetles visit such trees, pick up fungal spores, and unwittingly transmit them to healthy oaks.

Oak wilt is also spread below ground, through the root connections between adjacent oaks. Such root grafting is fairly common in areas with a large number of oaks, though it may be affected by the specific species of tree, as well as the type of soil and terrain. 


It is important to note that the symptoms of oak wilt will differ depending on whether the affected tree is a red or a white oak. As the disease's name would imply, both species of oak will display wilting--and then browning--leaves. In red oaks, discoloration will begin at the tips and the edges of leaves, gradually progressing closer to the base of the leaf rib. Initially, the leaves will take on a water-soaked look, which will soon progress to browning and then leaf loss. Leaves may begin falling from red oaks in as few as four weeks following infection.

White oaks tend to present slightly different symptoms. Here the discoloration symptoms are somewhat more irregular, although the still tend to progress from the outer to the inner portion of the leaves. Browning will occur at a much less rapid rate, and will tend to progress along a single large branch. When the bark is peeled back from an infected branch of the tree, it will display a dark brownish to blackish discoloration. For more information, visit websites like