Oak Wilt is a contagious fungal disease that can kill most species within just a few months. While an outbreak often starts with sap-seeking beetles which carry fungal spores from an infected tree to an open wound or fresh cut of a healthy tree, the disease then quickly spreads to nearby oaks via interconnected root systems at a rate of approximately 75 ft per year. Drought can slow progression, while frequent rainfall and mild temperatures may accelerate it.

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Once an outbreak starts it's nearly impossible to contain. Fungicide injections can avert death of most oak species, but the mortality rate without properly timed and administered treatment averages 90% for Live Oaks. Fungicide treatment is typically 4x less expensive than removing a dead tree as mandated by both local ordinances and subdivision covenants, therefore WOHA encourages at-risk homeowners to be proactive and prepared.

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The disease has ravaged the subdivision's east side for two decades and could jump to the west side within a few years. The map below provides the latest subdivision status and identifies properties at varying degrees of risk.

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Selecting an Arborist. ​When risk is elevated, consulting a specially trained arborist is strongly recommended. While most licensed arborists posses the standard ISA certification, only a handful serving Bexar County have also been certified by Texas A&M Forest Service to properly administer Oak Wilt fungicide. Click to view a partial list of such firms.

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Fungicide Options. Fungicide is the only protocol scientifically verified by experts. ​Local arborists typically administer Propiconazole, which is recommended by Texas A&M Forest Service. This viscous formula is injected into the root flare via pressurized tanks. Some Whispering Oaks residents have experienced varying results with Propiconazole in recent years, even when administered professionally and within sufficient lead time.

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When this occurs, some arborists may be willing to follow up with Tebuconazole which is an alternative formulation commonly used in other states. It is less viscous and may be easier for an infected tree to digest. And while any follow up regimen should ideally be timed at least 12 months after the initial, experts advise the risk of adverse reaction from additional fungicide is low and may be the only strategy to save a symptomatic oak likely to die within months.

 

​​​Preparation and Planning. Timing is critical. The goal is to treat at-risk trees before becoming symptomatic which indicates damage to the vascular system needed to effectively circulate fungicide. Survival rates are significantly lower for oaks allowed to become symptomatic. Vigilant monitoring of nearby properties and gathering feedback from neighbors is the best method estimate disease proximity. The active ingredient will dissipate after approximately 12 months, so while treating prematurely poses little risk, it may provide little benefit. When in doubt, be proactive to safeguard high value trees.

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Spring and Fall are the ideal time to administer fungicide because an oak's vascular system is most active in warm weather, but may then go dormant in a hot summer or cold winter. Experts recommend slow, steady root watering via soaker hoses well in advance of application to ensure the tree is sufficiently hydrated and primed to circulate the fungicide. A second application may be wise within 12 to 24 months following depending upon the threat's surrounding longevity and the tree's response.

 

Remember, the disease can travel in-ground a significant distance annually and kills healthy oaks quickly. Monitor nearby properties to identify symptomatic trees and query neighbors because nearby treated trees may not show symptoms even while transferring the fungus to oaks closer to your property. If symptoms do appear, contact a qualified arborist immediately to avert tree damage and death.

 

Homeowner Responsibilities. ​​In 2025, most Units within Whispering Oaks ratified amendments to the Community Covenants establishing a common sense mitigation policy:

 

• Non-emergency pruning is prohibited during the risk high period of February through June. Removal of the entire tree may be conducted at any time.

• All cuts must be sealed within 30 minutes. Homeowners are responsible to properly supervise their contractors.

• Homeowners must promptly alert adjoining properties if the disease is discovered.

• Dead or dying trees pose a safety risk and must be removed in a timely manner. Stumps visible from the street must be ground to soil level.