My oak tree has brown wilting leaves in July, is it oak wilt?

Brown, wilting leaves on an oak in mid-summer are a classic red flag for oak wilt (Bretziella fagacearum), one of the most destructive tree diseases in the Midwest. However, several other conditions can mimic these symptoms, so proper diagnosis is critical.

Key signs of oak wilt:

• Leaves brown from the edges inward (margins first, then the whole leaf)
• Wilting progresses rapidly from the top of the canopy downward
• Red oaks can die within 4-6 weeks of first symptoms; white oaks decline more slowly
• Fungal mats may form under the bark of recently dead red oaks
• Leaf drop occurs while leaves are still partially green — a hallmark symptom

What to do next:

1. Do NOT prune — open wounds attract the sap beetles that spread oak wilt. Avoid pruning oaks from April through October in Wisconsin.
2. Contact your local DNR forester or a certified arborist for a confirmed diagnosis. Lab testing of symptomatic branch samples is the gold standard.
3. If confirmed, vibratory plow lines can sever root grafts between neighboring oaks to stop underground spread.
4. Propiconazole injections can protect high-value oaks that are not yet infected.

For a deeper dive, see our Oak Wilt Guide and Common Tree Diseases in Wisconsin. Time is critical — if you suspect oak wilt, act fast.