Don’t Put Your Oak Trees At Risk

While spring brings flowers and warm weather, it also increases the risk of accidentally killing your oak trees.

Oak wilt can kill an oak tree in as little as three weeks after becoming infected. While the disease is caused by a fungus, that fungus is often transmitted to new oak trees by tiny insects called picnic beetles. These beetles are attracted to oak trees after they are cut or damaged, and spread the fungus to the tree once they make contact with an open wound.

Oak wilt can infect a single tree or group of trees, and spread to other nearby oaks through the roots. Photo Credit: Joseph Obrien, USDA Forest Service,

Once an oak tree is infected, it can spread the disease to other nearby oak trees through their roots, which are often connected. This can kill all the oak trees in a forest or a neighborhood, if not stopped.

Since controlling an outbreak of oak wilt can be very difficult once a tree or group of trees have become infected, it’s best to prevent your trees from becoming infected to begin with. You should not prune or otherwise damage your oak trees from spring until after their leaves have fallen in the fall. Mid-April to mid-July is considered the period with the greatest risk of infection, however it’s best to avoid injuring oak trees from now through November.

It’s easiest to notice your tree is infected with oak wilt in the summer when the leaves are on the tree. You may notice leaves which suddenly turn brown and fall off the tree. The leaves often don’t turn completely brown, but will look mostly brown with patches of green (see photo).

Other disease and insect problems can cause defoliation in the summer. If you suspect your oak trees might be infected with oak wilt, or have any other tree-related problems, call the Shiawassee Conservation District at 989-723-8263 ext. 3.

Pictured above: Northern red oak leaves with symptoms of oak wilt. Photo Credit: Ryan Armbrust, Kansas Forest Service,