How to Prevent Oak Wilt: A Practical Guide for Homeowners and Property Managers

Oak wilt (caused by the fungus Bretziella fagacearum) is one of the most serious killers of oak trees in Michigan. It spreads in two ways:

1. Underground through root grafts between neighboring oaks (especially red oaks).
2. Above ground via sap-feeding beetles (nitidulids) that carry spores from infected trees to fresh wounds.

Once a tree is infected and showing symptoms, it cannot be cured. Prevention is the only reliable strategy.

1. Avoid Wounding Oaks During the High-Risk Season (April 15 – July 15, roughly)
• This is the #1 rule in avoiding an oak wilt infection.
• Sap-feeding beetles are most active when temperatures are above ~60 °F, but can be active at temperatures as low as 40-45 °F.
• Fresh pruning wounds, construction damage or storm damage attract these beetles like a magnet.
• If you must prune pin oaks or red oaks during this window (e.g., storm damage), immediately apply a wound dressing or latex paint to every cut larger than thumb-size. Research shows proper sealing dramatically reduces infection risk by masking the odors from pruning wounds that attract spore-carrying beetles.

2. Prune at the Correct Time of Year
• The safest time to prune oaks is during the dormant season: November 1 through March 31 (the colder the better).
• The second-safest window is late summer/early fall (after July 15 and before leaf drop).

3. Break Root Grafts Before Removing Infected Trees
• Red oaks and pin oaks die quickly from oak wilt (often within 3–8 months) and form fungal spore mats under the bark. These mats attract beetles that can pick up the    spores on their body and spread the disease to other oak trees.
• If a tree is confirmed positive (or strongly suspected), sever root connections to healthy neighboring oaks before removing the infected tree.
• Professional arborists use a vibratory plow or trenching machine to cut roots 4–5 feet deep in a circle away from the infected trunk.

4. Do Not Move Firewood from Infected Red Oaks
• Spore mats on dead red oaks remain viable for months. Moving firewood is the #1 way oak wilt jumps long distances to new neighborhoods or counties.
• Burn firewood where you buy it or harvest it.

5. Use Preventive Fungicide Injections (for high-value trees)
• Fungicide trunk injections performed by a professional arborist can protect healthy pin oaks and red oaks for ~2 years.
• This treatment is most effective when injected before infection reaches the tree.
• Fungicide trunk injections are commonly used around known infection centers, near construction zones, or on prized specimen trees.
• Macro-infusion or micro-injection systems both work.

6. Plant Wisely
• Diversify species. Avoid planting large blocks of only red oaks or only pin oaks.
• Choose resistant or less-susceptible species: white oaks (bur, chinkapin, swamp white, English) are much less vulnerable than red, pin, or black oaks.



By following these steps - especially the “no wounding in spring/summer” rule and proper root-graft disruption - you can dramatically reduce the chances of oak wilt establishing or spreading on your property. If you suspect oak wilt (rapid leaf browning/discoloration starting at the top in pin oaks or red oaks, call an ISA 
Certified Arborist immediately for lab confirmation and containment recommendations.