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5 Facts About Oak Wilt and Michigan Oak Trees

Oak Leaves

Oak wilt (Ceratocystis fagacearum) is an exotic tree disease that was first observed in the U.S. in the 1940s. The wilt is caused by a fungus that's spread by sap-sucking beetles.


In Michigan, around a dozen species of oak trees make up 10 percent of the forest volume in the state. Oak wilt threatens large stands of trees and may threaten trees on your property. Here are five facts about oak wilt.


1. Oak Wilt's Biggest Sign Is Dropping Leaves

If you notice your oak trees losing leaves in the summer, that's a big red flag. Check the leaves on the ground for their color and dryness. Look for discoloration starting at the end of the leaf tips. Leaves that appear bronzed, partly brown, and dry can indicate an oak wilt infestation. Brown and green areas may be sharply contrasted in the leaves, and the leaves will feel withered.


On the tree, oak wilt affects one branch at a time. Look for single branches of dying leaves if you suspect your oaks are infested. None of these signs is a sure diagnosis, but they are all symptoms of the disease.


2. Oak Wilt Kills Trees Within Weeks

The fungus responsible for oak wilt must have living trees to act as the host organism. The fungus attacks the vasculature of trees. It clogs the vessels that move sapwood and water through the trees.


Once the vessels are blocked, the trees begin dying. Affected oaks will typically die from the top down, with successive branches turning brown and withering. Trees can be completely killed within two to three weeks.


3. Oak Wilt Kills Entire Stands of Oaks

The oak wilt fungus must have a living host, so it rapidly spreads from tree to tree in oak stands. Some oak-wilt spread is the result of root transmission. Stands of oak trees often have roots that have joined or grafted under the soil. These interconnected roots make excellent and rapid vectors for the spread of oak wilt.


The fungus also uses last year's dead trees to create spore mats. These are soft, dark, sweet-smelling patches that attract sap-sucking insects like nitidulid beetles. The beetles enter and exit trees through cracks made in the spore mats and spread the fungus to other nearby trees.


Human activity also spreads the oak wilt fungus. It can be transmitted via firewood and construction projects.


4. Oak Wilt Stops Only When All Adjacent Trees Die

If left unchecked, all oaks in a stand will die. Cutting out affected parts of trees only speeds up the transmission of oak wilt.


A tree service can help you diagnose the disease of oak wilt and help you decide on the best ways to manage an outbreak on your trees. One vital step to take is determining the boundaries of the affected trees. Once you know where the fungus stops, you can control the perimeter.


Two methods to consider are:

  • Removing all trees and roots inside the perimeter

  • Double-girdling and applying herbicide to perimeter trees


In the case of a single tree becoming infected, you might be able to halt the spread of oak wilt by having the tree felled and the stump pulled. You can also use fungistat chemicals to stop the oak wilt fungus from sprouting.


5. Oak Trees Should Be Protected After Pruning

Experts recommend that you avoid pruning or cutting oak trees between the months of April and September. These months are prime months for the spread of oak wilt through open cuts on trees.


If oak trees must be pruned, hire an expert tree service to handle the task. They can coat the exposed surfaces of the oaks with protective treatment after pruning and trimming.


Contact the climbing experts at J & B Professional Tree Service, Inc., to have your trees professionally trimmed, cut down, or pruned. We identify and provide treatment for tree diseases in and around the Portage, Michigan region.