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On December 16, 2021, Robert Hawthorne of the Texas A&M Forest Service spoke to us about the presence of oak wilt in Royal Highlands. For those who did not attend that meeting, below is a summary of the information Mr. Hawthorne conveyed. 

What is oak wilt? A tree disease spread by a tiny beetle and/or through its root system. When a red oak contracts oak wilt, its branches begin to get infected. When the tree senses an infected limb, it cuts off nutrition to that limb as a defense mechanism. But there is a lag between the time the limbs become infected and the time the tree senses infection. Therefore, the tree ends up killing multiple limbs all at once, in essence choking itself to death.

How do beetles spread oak wilt? When a tree dies of oak wilt, a fungal mat grows under the bark, the bark pushes away from the tree, a smell is emitted that attracts beetles, beetles eat the fungal mat all the while picking up spores on their bellies, and then they fly away. Those same beetles are also attracted to the smell of the sap in wounded trees (trees that have been trimmed at the wrong time of year or have lost limbs in storms), so they fly to those trees and eat the sap, spreading the oak wilt spores on their bellies to the new tree.

How is oak wilt spread through the root system? As oak trees grow (after about 10 years of growth), they develop a shared root system with other oaks in the area. An oak tree infected with oak wilt can infect other oaks that share its root system up to approx. 75 feet away.

How can I tell if a tree has oak wilt? Examine its leaves for veinal necrosis—when the skeletal vein system of the leaf turns brown while the rest of the leaf remains green. Sometimes only the center rib of the leaf turns brown, sometimes the tips of the leaves turn brown, and sometimes both happens. A tree has oak wilt if the entire tree (not just one branch) has leaves with veinal necrosis, if the tree drops healthy green leaves in the spring or summer, or if the tree’s leaves turn a brown/bronze color but stay on the tree.

How can I treat oak wilt? The most effective treatment is by injecting it with a fungicide. If you treat an infected oak early, as soon as you start to see signs of infection, the survival rate is 75%-80%. (Note that even if the tree lives, it will not look healthy for a few years,) The A&M Forest Service recommends hiring an ISA-certified arborist to do a macro injection through root flare, which involves drilling into the base of the tree and using a pressurized tank to hold a fungicide solution against the roots but not so pressurized that it damages the root system. Even better, hire an ISA-certified arborist who is also oak wilt qualified. (See www.texasoakwilt.org for a list of recommended arborists. Most charge $13-$15 per diameter inch of tree.) Fungicide treatments last 2-3 years, so if after that there is still oak wilt ion nearby trees, the tree should be injected again.

When should I have my oak injected? The best time for fungicide injections is in the spring and summer, when the tree is actively growing. However, if you see signs of oak wilt, do not wait. The sooner you treat it, the better. 

Can I prevent my tree from getting oak wilt? Yes, with proper tree care and preventive fungicide treatment when needed. 

What is proper tree care? Stay on top of pruning your trees to reduce the likelihood of the tree sustaining damage in storms (so broken branches don’t attract beetles). The best time to prune is in the fall, or perhaps in the winter, but never prune them February through July. The worst time to prune is in the spring, when they are actively growing. Note you rarely need to fertilize trees, especially if you are already fertilizing your yard.

When should I consider doing a preventive fungicide treatment Trees have an even higher survival rate if the fungicide treatment is done before the tree is infected with oak wilt. If you notice oak wilt in any trees within 150 feet of your trees, the Forest Service recommends injecting your tree with fungicide as a preventive measure. This gives you a little leeway, since the disease typically can move a distance of 75 feet. If the nearest infected tree is more than 150 feet away, it is too soon to inject fungicide. 

What should I do if my tree dies of oak wilt? Cut it down ASAP to reduce the chance of infecting other trees. Be sure to grind the stump out. The best time to replant an oak is in the fall so the root system can get in place before the spring growing season. It is better to plant a different species from other oaks in your yard because a higher species diversity increases resilience against disturbances.

Is there currently oak wilt in Royal Highlands? Mr. Hawthorne said it looks like there is oak wilt in the area but we will not know for sure until the spring when we can examine the new leaves. Be on the lookout in March and April. As soon as you notice signs of oak wilt on your trees or on your nearby neighbors’ trees, hire an arborist to inject your trees with fungicide.