Tree diseases and infestations

Oak Wilt

Oak wilt is a fungal disease that can affect all types of oaks. Red oaks are particularly susceptible and can die very quickly once infected with the fungus.

Help prevent the spread of oak wilt by not pruning or removing oaks from April-July. This is the highest risk time for the fungus to spread.

Learn more about oak wilt:

• University of Minnesota Extension - Oak Wilt
• Minnesota Department of Natural Resources - Oak Wilt

Twolined chestnut borer

Twolined chestnut borer is a native beetle that often attacks stressed oaks. Help trees during dry stretches with regular watering. Symptoms of twolined chestnut borer may look similar to oak wilt. 

Bur oak blight

Bur oak blight is a fungal disease that affects bur oak trees. Leaves will brown and drop in late summer-early fall. Most bur oaks aren't severely affected by the fungus. Over time, the tree may become stressed and more susceptible to other problems.

• MN DNR - Bur oak blight

See the page on emerald ash borer

Additional resources:

• University of Minnesota Extension - Emerald Ash Borer
• Minnesota Department of Natural Resources - Emerald Ash Borer
• How to identify an ash tree

If you have an elm tree, it may be at risk for Dutch elm disease. The first symptom of Dutch elm disease is branches of yellowing leaves near the top of the tree. If you notice this early in the summer, call a certified arborist immediately.

• University of Minnesota Extension - Dutch Elm Disease
• Dutch elm disease-resistant elm trees

• University of Minnesota Extension’s plant diagnosis guide
• Helping trees to manage stress