Oak Wilt in Minnesota: What You Need to Know

Oak wilt is a lethal fungal disease that has been spreading across Minnesota, threatening both red and white oak species. Understanding this disease is critical for protecting your oak trees and our urban forests.

What Causes Oak Wilt?

Oak wilt is caused by the fungus Bretziella fagacearum. It spreads through two primary pathways:

• Underground root grafts: Nearby oak trees often share interconnected root systems, allowing the fungus to spread from tree to tree below ground
• Overland transmission: Sap-feeding beetles carry spores from infected trees to fresh wounds on healthy trees

Recognizing Symptoms

Symptoms vary by oak species. Red oaks can die within weeks, showing rapid leaf discoloration from the edges inward. White oaks decline more slowly, with individual branch dieback over several years. Watch for these key signs:

• Leaves turning brown from the edges or tips inward
• Rapid leaf drop in mid-summer (especially in red oaks)
• Wilting that progresses from the top of the crown downward
• Fungal mats forming under the bark of dead trees

Prevention

The most important prevention step is avoiding pruning oaks during high-risk months (April through July in Minnesota). Fresh pruning wounds attract the beetles that spread oak wilt spores. If a tree must be pruned or is accidentally wounded during this period, seal the wound immediately with tree-wound paint or latex paint.

Additional Prevention Steps

• Don't move firewood from infected areas
• Destroy (by burning or burying) wood from infected trees
• Install root barriers between infected and healthy oaks
• Monitor your oaks regularly for early symptoms

Treatment Options

While there is no cure for oak wilt, treatment options include root barrier installation to prevent underground spread and fungicide injections (propiconazole) for high-value trees. Early detection and intervention are critical to saving surrounding trees.

Get Help

If you suspect oak wilt on your property, contact us immediately. Early action can help save surrounding trees and slow the spread of this devastating disease.