08/31/2026
Hypoxylon canker and oak wilt
Both fatal fungal diseases that affect oak trees, but they have different causes and behaviors. Hypoxylon canker is an opportunistic disease targeting drought-stressed trees, whereas oak wilt is an aggressive vascular pathogen that actively spreads from tree to tree through root grafts and insects.Cause and SpreadHypoxylon Canker: Caused by the fungus Biscogniauxia atropunctata. It lives latently in many trees and only turns aggressive when a tree suffers severe environmental stress, like a major drought. It does not actively jump to healthy, unstressed trees.Oak Wilt: Caused by the fungus Bretziella fagacearum. It actively moves through the water-conducting tissues of the tree and spreads aggressively across landscapes via sap-feeding beetles or underground through connected root systems (root grafts).Symptoms and IdentificationHypoxylon Canker:Upper canopy thinning, small leaves, and branch dieback progressing downward.Bark sloughs off in large patches.Exposes distinct, large crust-like fungal mats (stroma) that change from brown or gray to a prominent ashy black.Oak Wilt:Rapid leaf discoloration (bronzing or yellowing from the edges inward).Sudden wilting and defoliation, often dropping leaves while they are still green or partially green.Spreads rapidly through red oak groups (killing trees in weeks to months), while white oaks decline more slowly. Does not feature the large black peeling fungal crusts characteristic of Hypoxylon.Management and PreventionHypoxylon Canker:No chemical cure exists.Prevent by reducing tree stress through deep watering during dry spells and avoiding root damage.Remove severely infected, structurally unstable trees to prevent safety hazards.Oak Wilt:Management requires professional intervention, including chemical injections (like propiconazole) for high-value trees and physical root trenching to stop underground spread between neighboring trees.Avoid pruning oaks during high-risk periods (spring/early summer) when sap it at it highest.
Can you spot the signs and tell the difference between oak will and Hypoxylon canker?
