What Is Oak Wilt? A Complete Guide

We enjoy trees for the beauty and shade they bring to our surroundings. Oak trees, a beloved addition to many a yard, are under threat of multiple diseases. One such disease, oak wilt, can be fatal and spread to other trees if left untreated. Let’s review how you can protect your oaks from harm caused by oak wilt. 

What Is Oak Wilt? 

An aggressive fungus, known as Bretziella fagacearum, causes oaks to wilt and die. It grows through a healthy tree’s water conduction system after introduction by sap-feeding beetles carrying oak wilt spores or through root grafts. After a tree dies, fungal mats bearing these spores develop under the bark in the fall or spring of the following year. 

Oak wilt affects trees in North America, and more specifically, in the Midwest and Texas. All oak types are susceptible, but red-black oaks and Texas live oaks are at higher risk than those in the white oak group (bur, chinquapin, post, and swamp white). As white oaks are more resistant to the disease, they are more likely to survive.

Signs of Oak Wilt

Oak wilt has different symptoms, depending on the oak group affected. If you see these symptoms in your oak tree and want an accurate diagnosis, hire an arborist or tree maintenance company in your area for a professional assessment.

Red Oak Symptoms of Oak Wilt

Red oak varieties can die three to six weeks after the initial symptoms of oak wilt. Stay on the lookout for these warning signs:

• Top leaves suddenly wilt

• Premature leaf drop, moving from from the crown down until the tree is defoliated. 

Live Oak Symptoms of Oak Wilt

Live oak varieties take about a year to die from oak wilt without treatment. Stay on the lookout for these warning signs:

• Develops brown veins in their leaves 

• Leaves wilt and bronze, falling before they become totally discolored

• Lose their leaves over a three- to six-month period 

White Oak Symptoms of Oak Wilt

Luckily, white oak trees can live up to 20 years after oak wilt infection. Stay on the lookout for these warning signs:

• Show slow wilt of their branches

• Leaves turn brown and begin to fall from the tree

• Annual rings may discolor

How to Treat and Prevent Oak Wilt

If your tree has oak wilt, an arborist or tree maintenance professional can guide you in its treatments for managing the disease in the following ways: 

• Scheduling pruning for a specific time of year: Oaks wounds can attract sap beetles that spread fungus; pruning should be minimized during the tree’s active growing season and carried out mostly during the dormant season when the insects are less active.

• Removing infected trees: Removing the affected oak can help prevent the spread of the disease to other trees. Infected wood should be properly disposed of away from healthier oak trees. 

• Severing root grafts: Root grafts can also spread oak—severing them controls the disease from passing to other trees.  

• Using fungicides: Propiconazole is the most common fungicide for treating oak wilt. An injection into the trunk will slow its progression.