The Threat of Oak Wilt

Oak Wilt is a contagious fungal disease that can kill many species within just a few months. It often starts with sap-seeking beetles that transmit the disease to an open wound or unpainted cut, but it can then spread to nearby trees through shared root systems.

The East side of Whispering Oaks has battled an outbreak for several years with some success (details here).

Unfortunately, the disease is still progressing and some residents have been caught off guard recently, resulting in costly tree removal which can undermine a property's appeal and value.

WOHA has partnered with Texas A&M Forest Service to provide answers some of the most common questions about the disease and enable access to properly certified arborists. Helpful information can be found on its website.

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Frequently Asked Questions 


What is Oak Wilt?  Ceratocystis fagacearum is a fungal disease that affects the vascular function of Oak trees. It is contagious and can kill some species in just a few months. Many communities in Texas have been ravaged by outbreaks in recent years and Whispering Oaks is one of them.


How is it spread?  An infected Oak can pass the disease to others nearby via interconnected root systems. Live Oaks, which are common in Whispering Oaks, are particularly vulnerable to root transmission which is the driving factor behind of our outbreak’s expansion. Separately, tools from careless and inexperienced tree trimming workers can also spread the fungus between trees. Some varieties of sap-seeking beetles also carry fungal spores which can be transmitted to a fresh cut or wound that was not sealed immediately. Outbreaks often start with a beetle, but spread via roots.


Which Oaks are susceptible?  All Oaks are vulnerable in varying degrees. The two types of Oaks in Texas (Red and White) are affected differently. Those in the Red grouping are the most susceptible to the disease, deteriorate quickly, and are the least responsive to treatment once infected. Oaks in the White grouping are also at risk, particularly the prevalent Live Oaks which deteriorate somewhat more slowly and respond better to treatment if caught early.

How lethal is this threat?  Trees in Red Oak grouping have a 0% survival rate once infected. Infected Live Oaks have a 10% survival rate if left untreated, but the survivors are permanently damaged and often disfigured. Other species within the White Oak grouping have some natural resistance, however these trees are far less common in our area.


How can I tell if which type of Oak tree is on my property?  Compare leaves to books or web sites such as Texas A&M’s which provides helpful illustrations. When in doubt, contact a licensed arborist.


Why is the Whispering Oaks outbreak spreading?  Total containment of Oak Wilt is difficult in suburban settings where Live Oaks are plentiful because the fungus is transmitted among root systems. Experts advise a typical outbreak spreads approximately 75 feet per year. The best strategy is to maintain a prevention regimen until the threat from nearby trees has dissipated.


If the disease hasn’t reached my property yet, when should I take action?  Because Oak roots can extend 2-3 times the height of the tree, healthy high-value trees within 100 feet of an infected tree merit protective action. Prevention timing is critical, since not all Oak species can be saved once infected.


How can I protect my trees from Oak Wilt?  Injection of the fungicide AlamoTM is currently the most reliable and cost effective prevention for trees at immediate risk of contamination. All Oak species can benefit from well-timed preventative treatment. A qualified arborist inserts a medicinal drip into the tree base which permeates both limbs and roots within 3 days to inhibit infection if contact with the fungus occurs. Preventative treatment typically protects for over a year and should be repeated in 18 months if a threat remains within a 100 ft radius. Spring is the best time to enact a fungicide regimen. Only trust a licensed arborist to treat your trees. If your trees are already infected, see below.


How much does fungicide treatment cost?  Fungicide treatment cost varies by the size of the tree. Larger trees require larger dosages. Pricing is typically determined per diameter inch when measuring the trunk 48” above ground. Timely treatment is almost always far less costly than removal of a dead tree.


What about trenching?  Trenching severs tree roots to inhibit cross contamination. This technique is costly, disruptive and simply not feasible for all sites. Several years ago, Whispering Oaks used trenching on the Eastern side, and although this effort may have slowed the spread of the disease, it appears full containment was not achieved. Other nearby communities have found similar results. Trenching is now rarely recommended by Texas A&M Forest Service.

How can I tell if a tree on my property is already infected?  Live Oaks typically show yellow or brown veins in their leaves when infection has taken hold. Dry leaf tips and edges may also be a symptom. Species within the Red Oak grouping can be more difficult to detect. Contact a licensed arborist if your Oak’s leaves turn dull green or bronze, or appear water-soaked and wilt in the spring. In later stages, leaves curl around the midrib and are shed at branch tips. In the final stages, both green and symptomatic leaves throughout the crown will drop




What are treatment options for trees already infected?  The same fungicide regimen described above can be effective on many species, including Live Oaks, whose crown is less than 30% symptomatic. Early detection and treatment is critical because advanced infection hampers the tree’s vascular system and inhibits circulation of the fungicide. Treatment does not fully eradicate Oak Wilt from the tree, but it can significantly reduce its effects and prolong life.  Unfortunately, infected species within the Red Oak grouping typically do not merit treatment because by the time the tree is symptomatic, it’s often too late.


Can every Oak be saved?  No. Prevention can be costly and treatment won’t be effective in all cases. Individual property owners will need to determine which trees are worth saving. Some residents will prioritize larger trees or those that provide a strategic benefit such as home shading or curb appeal.


Should I consider removing Oaks as prevention?  This is strategy is controversial. Removing healthy trees may slow the inevitable spread of the disease within our community, but it also makes it more difficult to track the course of the outbreak. Property owners that only intend to apply preventative treatment to some, but not all, of their vulnerable trees may decide to remove less critical trees but still leave one or two sacrificial trees to announce the arrival of the disease within their property and closely monitor its impact. Consult an arborist before removing a tree.


If my neighbor pre-treated his trees, will this create a buffer zone for mine?  No. Even trees that are properly pre-treated with fungicide can still transmit the fungus to nearby trees via their root systems.


If I remove an infected tree, is it safe to keep the fire wood?  This is discouraged because the fungus can survive on unseasoned cut wood. Never store this wood from an infected tree near a healthy Oak.


Are moss balls a sign of trouble?  No. Moss balls commonly found on Oaks are not a sign of Oak Wilt infection and are non-parasitic organisms that do not pose any serious health risk to the tree. In fact, removing moss balls, particularly during the high risk February-June period can open wounds and attract beetles which may carry the fungus.


Should I take action now?  Yes. Look for signs of Oak Wilt nearby and talk to your neighbors on all sides to determine the level of risk to your property. Or contact a certified arborist who can identify threats within 100 ft and implement a prevention regimen if warranted.


Does the treatment pose a risk to my trees?  Yes. A small percentage of trees will react negatively to treatment which may result in lasting damage or death. Consult a certified arborist for more information.


Are there other treatment options?  There are alternatives to fungicide, however WOHA is currently advocating only treatment options recommended by the experts at Texas A&M Forest Service.


Why is protecting my Oak trees so important?  Trees are an important factor in your property’s value and also the namesake of Whispering Oaks. Experts warn that loss of prominent, mature trees can reduce a property’s value by up to 20%. Additionally, the cost of prevention is a fraction of dead tree removal costs. Be advised that San Antonio Municipal Code may mandate the removal of dead trees for safety reasons. Remember, 100% of Red Oaks and approximately 90% of infected Live Oaks will die once infected, and any survivors remain permanently damaged.