When oak wilt – a disease deadly to trees in the red oak family – was discovered in fall 2016 in trees at Belle Isle Park, the DNR quickly drafted a plan to contain and manage the disease in order to protect the historic forest and some of the state’s last remaining Shumard’s oaks.

Oak wilt is a fungus that can spread from tree to tree through underground root connections, or grafts. Overland spread also is possible when diseased trees develop fungal mats. During the growing season, the sweet-smelling fungus attracts sap-feeding beetles that carry fungal spores to other wounded trees in much the same way as bees transport pollen. If not treated, oak wilt will continue to spread and can potentially kill all red oaks in a state park, forest or neighborhood. 


Oak wilt at Belle Isle

  • Oak wilt was detected in the rare flatwood forest - one of the last remaining Michigan forests of its kind - near the center of the island. 

  • A survey of Belle Isle’s oaks revealed the disease has been present for many years and may have killed as many as 112 dead trees 

  • Oak wilt has impacted nearly 48 acres of the island’s 200 acres of forest land.

  • It is likely that the oak wilt fungus came to Belle Isle on infected material like firewood. The movement of firewood can introduce sap-feeding beetles that move spores from an infected piece of wood (ie. firewood) to freshly pruned or injured trees. 

  • The placement of hot coals at the base of trees also affects the health of oaks on Belle Isle.


Control efforts
The DNR is making every effort to preserve as many oaks as possible and is taking swift action to control the spread of oak wilt. The following steps have been implemented and are planned:

  • Step 1 (September through October 2016): Extensive ground surveys covered the entire flatwood forest to delimit the extent of the disease. Crews completed the first management phase, severing the roots between infected and healthy trees using a plow outfitted with a special cutting blade.

  • Step 2 (late February 2017): Dead oaks will be cut down and removed. This work must be completed before fungal mats develop and allow the disease to spread. Many of the diseased trees slated for removal are located in the flatwoods forest, a sensitive habitat area. To prevent damage caused by heavy equipment, low-impact harvest techniques, including possible aid. 

  • Step 3 (spring 2017): Selected oaks in or near areas of known oak wilt will be injected with a fungistat that may prevent infection. Approximately 150 trees, including many of the island’s Shumard’s oaks, have been selected for treatment due to their landscape value. The DNR will continue to monitor for infected trees throughout the year.

  • Step 4 (summer and fall 2017): The DNR will continue to monitor for infected trees throughout the year. Early detection of future infestations will be critical for successful control.    


What can you do? 
Since 2009, Michigan state parks have lost more than 500,000 trees to disease and infestation and millions more have been lost statewide. It is likely that the oak wilt fungus came to Belle Isle on infected material like firewood. The DNR reminds travelers and state park visitors to leave wood at home and to instead buy and burn firewood at or near your destination – don’t bring it back home. Please consider the following:

  • Do not move firewood. Oak wilt is spread by the movement of infected wood. Hauling firewood, even a short distance, from one part of the state to another is a common way for invasive tree insects and diseases to move to new locations.  

  • Do not prune oak trees during the growing season. Wait until trees are dormant to prune. Sap-feeding beetles are attracted to wounds caused by pruning and can carry spores from one infected tree to another. If you must prune, seal fresh wounds with paint to prevent contact with beetles. 

  • Look for and report signs of oak wilt, including sudden leaf drop or leaf color change in summer or patches of dead oaks, to DNR-FRD-Forest-Health@michigan.gov or 517-284-5895.



This project was funded in part with funds from the Michigan Invasive Species Grant Program through the Departments of Natural Resources, Environmental Quality and Agriculture and Rural Development.