By Mary-Jane Pilgrim, Master Gardener
Oak trees are an essential part of Ontario’s natural beauty, providing shade, wildlife habitat, and a sense of nostalgia. However, these majestic trees face a silent threat known as oak wilt, a deadly fungal disease that can devastate entire oak populations if left unchecked. In this article, we’ll discuss what oak wilt is and how you can help prevent its spread.
What is Oak Wilt? Oak wilt is a disease caused by the fungus Bretziella fagacearum. It primarily affects oak trees, especially red oaks and pin oaks. The fungus clogs the tree’s water-conducting vessels, causing wilting, leaf loss, and eventually death. Oak wilt is highly contagious, spreading through root grafts between neighboring trees or by sap-feeding beetles that transport the fungus spores.
Preventing Oak Wilt:
- Avoid Pruning Oaks in Spring and Early Summer: Oak wilt spores are most active during these seasons. Pruning creates wounds that can attract sap-feeding beetles carrying the fungus. Instead, prune oak trees during the dormant season in late fall or winter.
- Use Pruning Paint: After pruning, seal the wounds with pruning paint or a latex-based paint to prevent beetles from entering and spreading the disease.
- Dispose of Infected Wood Properly: If you suspect oak wilt, remove and destroy infected wood by burning or burying it. Do not use it for firewood or mulch.
- Report Suspected Cases: If you notice oak trees showing signs of oak wilt, contact your local forestry department or arborist immediately. Early detection and intervention can help contain the disease. This link may help: Signs and Symptoms of Oak Wilt.
- Promote Tree Health: Healthy trees are less susceptible to oak wilt. Ensure your oaks receive proper care, including regular watering, fertilization, and protection from other stressors like construction damage.
Oak Wilt has been found in the following locations in Ontario: City of Niagara Falls, township of Springwater (north of Barrie), and Niagara-on-the-Lake, ON.
There is currently no available treatment for oak wilt.
We must take collective action to protect our oak trees from oak wilt. By following these prevention measures and staying vigilant, we can help preserve the beauty and ecological importance of these remarkable trees for generations to come.
Resources
https://www.michiganoakwilt.org/oak-wilt-101, especially this image showing the disease on both red and white oak leaves.
https://www.invasivespeciescentre.ca/invasive-species/meet-the-species/invasive-pathogens/oak-wilt/
The Peterborough & Area Master Gardeners 