Oak Wilt

Important Oak Wilt Information
updated January, 2004 Photo of Tree with Oak Wilt

Oak wilt is a fast tree-killing disease of oaks. It's a disease caused by a fungus (Ceratocystis fagacearum). The fungus plugs the water-conducting tubes in a tree, and as the transportation of water throughout a tree is stopped, leaves wilt and fall off. The tree most often dies as a result. Oak wilt is common in the Stevens Point area.

Oaks can be categorized into two groups; the red oak group and the white oak group. The red oak group (black, northern red, northern pin and others with pointed leaf margins) is more susceptible. When oak wilt affects the red oak group, the entire tree may wilt, or lose all of its leaves, in just a couple weeks. Most often this occurs from late June throughout July. Many times diseased trees occur in groups. The white oak group (white, bur, swamp white and others with rounded leaf margins), is less susceptible. When oak wilt affects the white oak group, trees usually die slowly, many times only a branch or two may die each year. Most often it takes a few years before the entire tree succumbs to the disease. In both groups, the tree typically dies from the top down, and leaves turn brown from the tips to the base.

The disease can be spread in one of two ways; by root grafts and by insect vectors. The roots of individual oak trees can graft to each other, and if a diseased tree's roots are grafted to a healthy tree, most times, especially in the red oak group, the disease is taken up by the healthy tree. The disease can keep spreading this way from oak to oak. There are beetles that are attracted to fungal mats that some diseased trees produce. When the beetles feed on the sweet smelling mats, fungal spores stick to the beetles bodies. If the beetle then moves onto a healthy, but freshly wounded oak tree, the disease-causing spores are introduced to that tree. Photo of Severing Roots

The best control measure against the disease is prevention. Do not injure, prune, or cut oaks from April 1 to October 1. It is during this time that oaks are most susceptible. Oaks can still get infected during the rest of the summer months, but it's less likely. If an oak is wounded during this period, it's one of the few times it's recommended to apply tree wound paint to the injured area. If pruning oaks around your house, or clearing an oak lot for a house, it's advisable to do so during the winter months.

Severing root grafts between healthy and infected oaks is one way of stopping the spread of the disease. A tree care professional and Diggers Hotline should be contacted before this method is attempted. The wood of a newly infected tree that is cut down, needs to be debarked, burned, buried, or covered with a tarp and the sides sealed for a year. This will prevent the beetles from feeding on any fungal mats that may form in the firewood.

There are other oak wilt management strategies available, such as injecting fungicides that help prevent the disease, that a tree care professional, city forester, or county extension agent may be able to offer or suggest to you. Photo of Fungicide Injection

To confirm that your tree has oak wilt, samples can be sent to the Wisconsin Department of Agriculture Plant Industry Laboratory. For more information on how to do this, or for any other questions pertaining to oak wilt, please feel free to E-Mail the Stevens Point Forestry Department, or call us at (715) 346-1532.

For more information about Oak Wilt, visit the Wisconsin DNR's Oak Wilt website.