Disease

Oak wilt

Bretziella fagacearum

A fungus that blocks the water flow in oaks. Red and black oaks (pointed leaf lobes) can die in a few weeks; white and bur oaks (rounded lobes) decline more slowly. It spreads through grafted roots and by sap beetles to fresh wounds in spring.

Signs

• Leaves turn dull green or bronze from the tips and edges inward and drop quickly, often with green centers.
• On red oaks, rapid leaf loss from the top of the crown down.
• On red oaks, fungal mats under cracked bark that smell like fermenting fruit; patches of dying oaks that spread outward through the roots.

What favors it

Pruning or wounding oaks in spring and early summer, when sap beetles carry spores to fresh wounds, and root grafts between oaks of the same group.

Prevention

• Do not prune or wound oaks from April through July (February through June in Texas).
• If an oak is wounded, cover the wound right away with latex paint or wound dressing, especially in that window.
• Do not move oak firewood from diseased trees unless it is debarked, dried a year, or tarped.

Crops it shows up on

Shade & ornamental trees.

Often confused with

Sources

• Oak wiltMinnesota Department of Natural Resources
• Oak WiltUniversity of Wisconsin-Madison Extension
• Oak wilt in MinnesotaUniversity of Minnesota Extension
• How to Identify and Manage Oak Wilt in TexasTexas A&M AgriLife Extension

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