Oak Wilt Management

Introduction to Oak Wilt

Oak Wilt is the single most devasting disease affecting our native Oak (Quercus spp.) species, here in the Midwest.  It is caused by an invasive fungus (Bretziella fagacearum) that invades the tree’s vascular tissue either through a wound (vectored by certain sap and bark beetles) or via root grafting from adjacent trees that are infected.  Once introduced into the tree, the fungus “plugs” up the tree’s conductive tissue, as the tree forms tyloses to defend itself from the invading fungus.

New infections from beetle vectors typically occur during the “high risk” period (April – July), in spring and early summer, but can occur throughout the growing season.  For this reason, do not prune Oaks from April – November most years, unless unavoidable due to storms or safety issues.  Do not move diseased oak firewood for the same reason; you will increase the risk of spreading disease.

Trees in the Red Oak group are most vulnerable to severe Oak Wilt disease and, once infected, will typically die rapidly over the course of 1-2 months. Red Oaks are also more likely to produce spore mats, which attract beetle vectors, the spring after succumbing to Oak Wilt.  Preventative treatments on the only option preventing Oak Wilt in Red Oaks, as post-infection therapy will not yield success.  The White Oak group is also susceptible to Oak Wilt, but therapeutic intervention may be warranted depending on severity.  

Oak Wilt Signs & Symptoms of Infection

An initial indicator of Oak Wilt infection is premature and excessive leaf drop during summer months. Leaves turn a dull or off-green color (sometimes referred to having a “water soaked” appearance), turn brown, curl, and begin dropping. Characteristic leaf discoloration is typically first noticed around leaf tips and margins (edges), before progressing inward and towards the base. Symptoms of new infections are most apparent in later spring, extending into June or early July, but can occur anytime throughout the summer months.

Oak Wilt Treatment / Management

Managing Oak Wilt can be complex, as the disease can spread via root grafts to adjacent trees. In ideal settings, we recommend root graft trenching with a vibratory plow and chemical infusion with Propiconazole. Root graft disruption is not always feasible in urban settings due to buried utilities, property boundary restrictions, lack of proper equipment, and other factors. If root grafting is suspected, removing diseased trees should only occur during the dormant season, otherwise expedited spread to neighboring oak tree is likely.

We treat Oak Wilt with a low volume, macro-infusion system containing Alamo (Propiconazole 14.3%) systemic fungicide and water. This treatment will prevent the overland spread of Oak Wilt for up to 2 years. We inject/infused this directly into the tree’s root flare area. This fungicide also is translocated to the tree’s root system and can help slow the spread via root grafting, though it is unlikely to save a tree with Ceratocystis already in its roots (especially Red Oaks).