ST. CLAIR COUNTY, Mich. – Invasive beech leaf disease has been found in a small private woodlot in southern St. Clair County, according to the Michigan Department of Natural Resources.
This is the first time it’s been confirmed in Michigan. It’s associated with the microscopic worm Litylenchus crenatae, a nematode.
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The worm enters and spends the winter in leaf buds. This causes damage to the leaf tissue on American, European and Asian beech species.
Trees that are weakened by leaf damage become susceptible to other diseases and can die within six to 10 years after initial symptoms.
There are around 37 million American beech trees in Michigan. You can identify them by their smooth bark. They provide food and shelter for wildlife.
Read: What are invasive jumping worms and what threat do they pose to Michigan?
How was the outbreak found?
The owners of the land found stunted, odd-shaped leaves on young beech trees in a wooded area on their property.
They reported the suspected outbreak through the Midwest Invasive Species Information Network.
DNR forest health staff took samples for testing by the Michigan State University Forest Pathology Laboratory. Results were confirmed by the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service.
“Though beech leaf disease was detected this spring, the condition of the leaves and number of trees affected at this location suggest the disease has been there for more than a year,” said Simeon Wright, DNR forest health specialist. “Because symptoms are slow to emerge, it is difficult to detect the disease before it is established.”
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No known treatment for beech leaf disease
There is no known treatment for beech leaf diseases.
If it spreads through Michigan it could have a “devastating” effect on beech trees. The disease was first detected in Ohio in 2012. It was then found in other states and Ontario. There are nine states with confirmed cases of beech leaf disease.
It is possible the disease spread through the movement of infested nursery stock and other beech material containing leaves and buds. Beech trees, tree material and firewood should not be moved from areas of known infestation.
Beech trees are already under attack from beech bark disease.
What are the symptoms?
The nematodes are associated with damaged leaf tissue, dead buds and darkened, thick tissue bands between leaf bands.
The bands create a striped effect on the leaves. Officials said it’s easier to notice by looking upward at trees on a sunny day.
The leaf curling and distortion progress over time, resulting in withered, dried or yellow leaves and a thin canopy. Leaf loss is noticeable in early summer on heavily infested trees.
Why is it a problem?
Officials said very little is known about the disease. It’s unclear if the nematode is the primary cause of the disease or just a carrier of another agent responsible for the disease.
”Many questions about beech leaf disease remain unanswered,” said Wright. “Because of this, we don’t yet know all the ways the disease might be spread, and currently there are no known treatments to protect trees or reduce disease impacts. State agencies are working with the U.S. Forest Service, several other states, Ontario and Michigan State University to better understand the disease and the potential effects it will have in Michigan’s forests.”
Read: Let’s talk about Michigan’s invasive aquatic plants: How to identify them and the dangers they pose
What are officials doing?
The disease was added to Michigan’s invasive species watch list in January 2021.
The DNR will train Michigan’s cooperative invasive species management area staff on how to ID the disease and take samples from trees they suspect are infested.
CISMAs will assist the DNR and MDARD in sharing information on beech leaf disease with the public, partners and stakeholders in the nursery and tree care industries.
A quarantine is not being issued because it’s not clear how the disease is spread.
What can you do?
If you believe you have found a symptomatic tree you should take photos, including close-ups of the leaves. Take note of the location, date and time -- then report the tree through one of the following ways:
- DNR Forest Health Division: Email DNR-FRD-Forest-Health@Michigan.gov or call 517-284-5895.
- Use the Midwest Invasive Species Information Network (MISIN) online reporting tool.
- Download the MISIN smartphone app and report from your phone – MISIN.MSU.edu/apps/.
Look-alike diseases
There are other, more common diseases that could be mistaken for beech leaf disease. They can be managed by regular tree maintenance or with the help of a certified aborist.
- Beech leaf curl aphid causes puckering and curling at the leaf margin, with aphids or their cast skins usually visible inside the curled areas of the leaf, but usually isn’t harmful to tree health.
- Erineum patch, caused by eriophyid mites, creates light green or yellowish to orange patches on the upper side of the leaf, rarely affecting overall tree health.
- Anthracnose creates small brown or black spots on leaves that eventually cause dead areas. New leaves may curl. Fungi infect leaves and stems and are most active in wet spring seasons, with a limited impact on tree health.
- Powdery mildew, affecting many trees and shrubs, causes beech leaves to turn yellow. It may cause defoliation but won’t kill beech trees.
Click here to learn more about beech leaf disease and other species on the watch list.