Gardening: Oak wilt disease could spread in Michigan

Nancy Szerlag
Special to The Detroit News

If you’re tired of talking politics at cocktail parties and picnics, I’ve got something new to chat about – oak wilt disease, and it may be coming to a yard near you.

“Oak wilt is a devastating vascular disease that is making its way into Michigan,” says plant pathologist David. L. Roberts, Ph.D. from Michigan State University. And we all need to spread the word about it so folks learn to properly care for these valuable trees.

The scary thing about this disease is in many cases it’s incurable. Members of the red oak family (those with very pointed leaf lobes, including pin oak, black oak and scarlet oak) are very susceptible and once they become infected can die in as little as four to eight weeks. If an infected tree is in close proximity to other oaks, the disease may spread from tree to tree through their interconnecting root systems known as root grafts.

If caught early, injections of the fungicide propiconizole, sold under various trade names, may cure some white oaks (those with rounded leaf lobes, including pin oaks, swamp oaks and burr oaks) infected with the fungus and prevent the spread of infection by root grafting.

Symptoms of oak wilt disease include premature leaf drop during fall and summer and leaf wilt.

The fungus is spread by the tiny black picnic beetle that’s attracted to injured oak trees by the fruity smell of the tree’s sap that runs from open wounds. So the first line of defense to prevent this devastating disease is to only prune oak trees when the trees are dormant. January and February are the safest months for pruning here in Michigan. Prime time for Oak wilt transmission is spring (April, May and June), but Dave Roberts and others believe it can be spread throughout the warm season.

If an oak needs pruning during warmer months, as a result of storm damage or other issues, the wounds should be sealed by painting them with tree paint within 12 to 24 hours. Roberts says for homeowners, latex paint also works well. If all you have in the garage is chartreuse left over from painting the kitchen, small sample cans of paint are sold at hardware stores and big boxes.

For more information on oak wilt and other tree disorders go to Roberts’ website at

To find a tree care professional, go to Roberts says ask for references and a certificate of insurance. And never let anyone going door to door touch your trees.

Nancy Szerlag is a master gardener and Metro Detroit freelance writer. Her column appears Fridays in Homestyle. To ask her a question go to and click on Ask Nancy. You can also read her previous columns at detroitnewscom/homestyle.