Oak Wilt is a lethal disease caused by the fungus Bretziella Fagacearum.

  • The fungus invades and disables the water conduction system in White, Red and other oak species.

  • Red Oaks typically die in 4-6 week of initial symptom development.

  • White Oaks may survive and take 1-6 months to defoliate and die.

  • Most Oak Wilt is spread through interconnected root grafts between different trees.

  • Root graft disruption and fungicidal treatments aid in prevention of disease spread.

The Spread of Oak Wilt

Sap feeding beetles (Nitidulidae) are the most common insect vector, but bark beetles (Scolytidae) have also been reported as a vector.

  • They feed on Oak Wild fungal spore mats that form underneath the bark.

  • They carry Oak Wilt spores to wounds on uninfected trees.

  • Overland transmission takes place between early spring and summer.

Because beetle vectors (carriers) are attracted to fresh wounds, it is important not to prune oaks during the season that spore mats are present. Prune only during the dormant season.

Root Graft Transmission

Root graft transmission is the most common mode of infection. Over 90% of all new Oak Wilt infections are transmitted in this manner. A roof graft is formed when the roots of two trees of the same species of oak meet and fuse together. The disease is then able to move from an infected tree into an uninfected tree.

Prompt Diagnosis

  • The primary symptom of Oak Wilt disease is the wilting of leaves and sudden defoliation. Browning begins on the margin of the leaf and moves inward, and there is a distinct line between the dead tissue and living tissue. Leaves normally fall before they are completely brown.

  • In Red and Pin Oaks, wilting progresses from the top of the canopy downward, while in White and Bur Oaks, the wilting may occur on the branches scattered throughout the tree.

  • Streaking of sapwood beneath the bark is a sign of the defense response of the tree and provides further evidence for Oak Wilt.

  • An additional sign of the disease is the presence of the fungal spore mats on Red and Pin Oaks. They split the bark open and attract insects with their fruity odor.

Isolate and Remove Infected Trees

An important aspect of Oak Wilt control is physical disruption of the root grafts between infected and healthy trees. This barrier disrupts the path of root graft spread and provides protection and can stop the spread of disease.

  • Vibratory trench lines are precisely measured and laid out in place by your Certified Arborist. Trenching is usually performed in the fall.

  • Vibratory trenching is the most effective and un-disruptive method to control disease spread.

  • Trees that died from Oak Wilt in the last year should be removed in the winter before the following spring.

  • Infected spore-producing wood needs to be destroyed properly. Ask your Arborist.

How Can You Protect Your Oak Trees?

  • Root graft disruption between healthy and infected trees.

  • Avoid Oak wounding or pruning between April and November.

  • Fungicide injections made directly into the vascular system of your tree.

  • Proper disposal of infected wood.

  • Educate your community and spread this fact sheet.

  • Call your Parshall Tree Care Experts Arborist with any questions.


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