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Oak wilt disease: What you need to know about it

By: Lacey Russell, PhD | May 16th, 2018

Oak wilt. It's nasty. Highly contagious. Fast-acting. Deadly. A tree disease that's been around for a little over 50 years and is wiping out oak trees across the country.

For homeowners in central and north Texas, it's an especially huge problem. Old and beautiful oaks have been dropping like flies from Dallas to Austin, and everywhere in between and around. And it's not just Texas. Oak wilt has become one of the most destructive tree diseases in the country.

The more educated homeowners get, the more we can work together to keep it under control. And that's exactly what it takes to protect our trees from a disease that spreads from yard to yard and tree to tree—neighbors joining forces.

Learn how to identify Texas tree diseases on your own

What is oak wilt Disease?

oak wilt texas

Oak wilt is a fungus that attacks a tree by blocking its vascular system and preventing water and nutrients from moving through the roots to the rest of the tree. The oak tree essentially dies of thirst and hunger. And it happens quickly.

How oak wilt spreads

Oak wilt can spread across trees, yards, and neighborhoods in a couple of ways:

  1. Sap feeding beetles carry the fungal spores on their bodies as they fly from tree to tree. The spores land on the tree bark and begin to form a fungal mat as they grow and thrive on your tree.
  2. The disease can also spread from one tree to another via underground grafted root systems. This is most common in live oaks.

Are my trees susceptible to oak wilt?

All oaks are susceptible to oak wilt, but some are more prone to the disease than others. Oak trees can be categorized into two large groups: red oaks and white oaks.

Red oaks

Red oaks include oaks such as shumard oak, Spanish oak, southern red oak and blackjack oak (among others). This group is more susceptible to the fungus than white oaks, and will typically die within two to five weeks after symptoms appear.

Unfortunately, many of us have red oaks such as shumard oak planted in our yards. They are great, fast-growing, beautiful shade trees. However, due to their high susceptibility for contracting the deadly disease, Treefix recommends against planting them.

White oaks

White oaks include post oak, bur oak, and Lacey oak (among others). This group is more resistant to the fungus than red oaks.

Live oaks

The types of white oaks that are most susceptible to oak wilt are live oaks. Live oaks often die from the disease, and it's happening in great numbers. Huge stands of live oaks have been devastated from oak wilt in the wilderness and in urban environments across the country.

An interconnected root system is to blame for the large loss of live oak trees to the disease. Live oaks develop root systems that connect with other live oaks, forming a network where they share water and nutrition. Sadly, this also means they can transmit an infectious disease from one tree to another. In fact, oak wilt can be a problem wherever live oaks are the dominant tree.

What does oak wilt look like?

Like many tree diseases, it can be difficult to diagnose, even by experts. However, there are some tell-tale signs of an infection.

Live oak trees show a wavy pattern on their leaves when they are infected. This is called veinal necrosis. If this symptom develops you can be pretty sure that your tree has oak wilt. Most live oaks lose their leaves and die over a period of one to six month after the first signs of the disease show up.

Other oak wilt signs

Unfortunately, not all live oaks display veinal necrosis. If your tree looks sick, find out if your neighbors or any near-by area is battling oak wilt. A professionally trained arborist can you help identify oak wilt and advise you on how to save your trees, if possible.

Wood samples may also be taken and sent to a lab where the fungus can be properly identified. However, this process usually takes at least two weeks, which may be too long to wait, depending of the stage of disease development.

Identifying oak wilt on red oaks can be a bit tricky. In early spring, the young leaves may simply wilt and turn pale green and brown. They usually remain attached to the tree for a while. The older, more mature leaves develop dark green water soaking symptoms or turn pale green or bronze starting at the tips of the leaves and moving inward. You may notice this on one branch before it quickly takes over the entire tree.

Unfortunately, Red oaks never survive oak wilt. The only solution is prevention. Red oaks often die within three to four weeks after the first appearance of symptoms. During summer months, diseased red oaks often can be spotted from a distance because of their bright autumn-like coloration in contrast to the surrounding greenery.

Another reliable indicator is a fungal mat found just under the bark of the tree. They often form in the spring on red oaks that developed the disease the previous year. You can find the fungal mats by looking for narrow cracks in the bark of dying red oaks. These cracks lead to hollow areas between the bark and the wood. They also have a distinctive odor similar to spoiled fruit.

Oak wilt prevention

Knowing the signs can help you identify if the disease is anywhere near your home. It's always a good idea to reach out to a professional if you have oak wilt in your neighborhood. They can help you and your neighbors take preventative steps to preventing your trees from becoming infected.

Tree care professionals are also aware of tree disease hot spots, and can help determine if your trees and neighborhood are at risk.

Only prune oak trees during the cooler months. This will help reduce the risk of attracting the fungus-carrying beetles to the open wounds. They're mainly active during warm months. Use wound paint or pruning spray immediately after pruning as well. The paint prevents spores from entering the tree’s sap and deters the insect from visiting the wound.

Firewood can transport the fungal spores. It’s a good idea to burn all the firewood you've stacked at your home by the end of winter. Because firewood can contain the fungus, it has been responsible for introducing the disease to oaks in different parts of town, or even in different parts of the state. In fact, transporting firewood around the state has been a major reason the tree disease has spread so rapidly.

Planting oaks other than live oaks and red oaks will also slow down the spread of this nasty tree fungus.

Finally, educate your neighbors about the devastating effects of oak wilt and what you can do to help prevent it from spreading to and through your neighborhood.

Oak wilt treatment

A professional arborist can help you manage the disease and save your trees. Oak wilt can often be managed so that infected trees survive and further spread is prevented.

Professionals use techniques such as trenching between trees to keep the disease from spreading through roots.

Oak Wilt Treatment

If used soon after infection, a fungicide can prevent the disease from infecting healthy trees and it can save infected trees. The fungicide is injected into the tree’s water-conducting vascular system through small holes drilled into the base of the tree. Treatment success depends on the health of your tree, the amount of fungicide applied, and the injection technique. Only trained applicators should apply the fungicide.

Oak wilt Texas: What you can do about it

1. Education

Learning about oak wilt disease and how to identify it is the first step in preventing it. You'll also want to stay in the know about infected neighborhoods around you.

2. Neighborhood Cooperation

Since oak wilt is so contagious and deadly, it's not only important to educate yourself, but you'll also want to educate your neighbors. Oak wilt doesn't care about fences. It doesn't care about property lines. If you want to prevent your trees from contracting it, the best way is to keep your neighbors' trees from contracting it.

Neighbors coming together and joining forces to stop the spread of oak wilt is not only an effective means of prevention—it's pretty cool, too :)