Our Strong, Resilient Nature

Understanding and Combating Oak Wilt in the Texas Hill Country

Article by Daniel Gertson

Photography by Daniel Gertson, Kevin Belter

Originally published in Boerne Lifestyle

Oak trees stand tall in the hills around us. Their majestic canopies are iconic in these parts, with mighty trunks and branches admired for their strength and resilience—traits shared by the people who live among them. But they face a dangerous pestilence, one that seems to strike like lightning and spread as fast as a summer wildfire. Oak Wilt: a disease always poised to devastate the region's cherished oaks.

All hope is not lost, however, according to two local experts. David Touchon is the Land Manager at Cibolo Center for Conservation, and Kevin Belter is a Board-Certified Master Arborist and president of Arbor Care and Consulting. These two men began combatting the scourge of Oak Wilt via different paths, but their passion for preserving the natural beauty of our landscapes is very much the same. 

Belter says diversity is vital. “We need to plant non-oaks. All oaks are susceptible, so diversification of tree species on a property will increase the value of that property.” Or as Touchon puts it, “I always say the wilder and the woolier, the better.”

Oak Wilt takes hold when trees are stressed and vulnerable. The fungus Bretziella fagacearum lives in the vascular tissue of the trees and invades when living tissue is exposed, often by pruning, a beetle feeding on sap, or a deer rubbing against the trunk. Once inside, the fungus disrupts the tree's water-conducting vessels, leading to wilting and eventually death.

The Texas Hill Country's warm and arid climate creates favorable conditions for Oak Wilt development. Prolonged drought and sudden freezing can weaken trees, making them more susceptible to infection. 

Recognizing the symptoms of Oak Wilt is crucial for early intervention. Infected trees often exhibit wilting or browning of leaves, starting at the top of the canopy and progressing downward. A distinct characteristic is the rapid discoloration of leaf veins, resulting in a browning pattern that resembles a lightning strike (see Belter’s website for a gallery of Oak Wilt images). As the disease advances, affected trees may shed their leaves prematurely, compounding the threat to the oak population.

Touchon says it can sometimes be difficult to conclusively identify Oak Wilt on your own, so you should always enlist the help of a professional before taking action. He says the “spline test” can help you know if a tree is dead or just dormant, “You get a branch and bend it down about three inches. If it cleanly breaks, snaps, dead. But just a bit of moisture… and then if it springs back, there's still moisture in there.” This test can’t tell you why a branch may be dead, so talk to a professional if you’re concerned about infection. Once it has been positively diagnosed, prevention and management become essential strategies because there is no cure.

Prevention and Treatment
Preventing the spread of Oak Wilt involves a combination of proactive measures. One primary strategy that Touchon advocates is to avoid pruning oak trees during the growing season, typically from February to June, when the beetles that transmit the fungus are most active. If pruning is necessary, it should be done during the dormant season, from July to January, to minimize infection risk.

But pruning practices can’t prevent all infections. “People talk about a lot about paint,” Belter says. “The massive problem with that is all the non-man-made wounds that will never get painted.” He says it’s important to eliminate spore-producing oaks prior to fungal mat formation. Fungicide injections can be effective in protecting valuable, healthy trees. However, the use of fungicides is not a one-size-fits-all solution and must be approached with careful consideration. Touchon says that some natural options—like sprinkling dried molasses around the base of a tree—can be helpful by improving the diversity of organisms in the soil, which helps the trees maintain overall health.

Ultimately, a united community effort is vital for effective Oak Wilt management. Local authorities, arborists, and residents must collaborate to raise awareness and implement preventive measures. Community workshops and educational programs can empower residents to identify symptoms, report potential cases, and implement best practices in Oak Wilt prevention. City- and state-run programs can help homeowners understand the best strategies to protect their land, and some will help offset the cost of removing highly susceptible trees from people’s property.

Touchon believes that nurturing a healthy, robust, native ecosystem will go a long way toward reducing the threat of Oak Wilt in the future. He and Belter agree that keeping various plants in and among our oaks will lead to a more robust, more beautiful Hill Country in the long run. As Touchon says, “Stop clearing so much. Leave some green on the ground and above you. You always say health through a nice mosaic.” | 210-279-6969 | 830-249-4616

“I always say the wilder and the woolier, the better.”

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