Texas has the highest concentration of oak trees in the United States. Oak wilt is a serious threat to our North Texas urban forest, infection centers among live oaks specifically expand at an average rate of 75 ft per year in Texas. What can Texans do?  

How to Identify Oak Wilt 

• Dead wood or defoliation in oaks
• Production of small leaves on trunks and large limbs after dieback
• Leaves with browning at edges (red oaks) or along veins (live oaks)
• Fungal mats forming on surface of wood, starting out gray- or buff-colored and turning black as they age
• Cracking and peeling bark
• Visible insect activity

While these signs do not necessarily indicate Oak Wilt, presence of one or more of them may indicate possible infection. A visit from a Tree Expert or Certified Arborist can help you to understand the health of your trees and plan out your next steps.

What Kind of Disease is Oak Wilt?

Oak wilt is an infectious disease caused by a fungus (Bretziella fagacearum*). All oaks (genus Quercus) are susceptible to oak wilt, but different species may react differently to the fungus. Oak wilt is a vascular disease, and infects the whole tree, even if only one part is symptomatic. As the fungus spread through the tree, it blocks the transmission of nutrients to the canopy, causing the characteristic “wilt,” or dieback.

In live oaks, infected leaves often show yellow-brown veins, even while still on the tree. In red oaks, leaves may simply wilt and brown. This process can lead to an autumn-like coloration during the summer. Additionally, fungal mats may form underneath the bark of red oaks, leading to cracking, peeling bark and a rotting smell.

While visual inspection is a strong indicator of the presence of the oak wilt fungus, laboratory confirmation may be required. The Texas Plant Disease Diagnostic Laboratory offers testing for oak wilt and many other diseases.

How do Trees get Oak Wilt?

The most common ways for the oak wilt fungus to be transmitted are by insect activity and root grafting. Insects can infect a tree through any exposed wood (not covered by bark) or open wound (such as a pruning cut, broken limb, or where branches rub against each other). In situations with oaks planted in close proximity, the fungus can be transmitted from one tree to another via underground root grafting. As roots make contact with other roots, they grow together and share pathogens.

Different species of oak can contract and spread oak wilt by different methods.

Red Oaks

Red oaks (Texas, Shumard, blackjack, water) are extremely susceptible to infection through insect activity. Red oaks are often the primary mode by which oak wilt gains a foothold in a new area. The oak wilt fungus thrives in red oaks and creates visible fungal mats underneath the bark. These spore mats attract insects; sap beetles of the Nitidulidae family are the most common type. Beetles feed in the infected area and become covered with particles from the spore mats. Drawn to exposed wood on healthy trees, the beetles transfer the fungal spores, spreading the infection.

Live Oaks

In contrast to red oaks, live oaks are susceptible to oak wilt primarily through their root systems. In nature, live oaks often grow in groups, sometimes called motts. Underneath the mott, the root systems of the individual trees become interconnected. This grafting allows not only nutrients to be shared, but pathogens as well. Once a member of the mott has contracted the oak wilt fungus, the infection quickly spreads.

White Oaks

White oaks (post, bur, chinkapin) are more resistant to oak wilt than other species, but are still at risk. Transmission generally occurs through spore transfer by insects, or by human activity.

Can you Prevent Oak Wilt?

Oak wilt is an epidemic. Because of the concentration and susceptibility of oaks in Texas, especially red oaks, it can be difficult to isolate centers of infection and prevent further spread. The Texas A&M Forest Service and the Forest Health Protection branch of the U.S. Department of Agriculture have issued some guidelines to help prevent further tree death.

• Remove and properly dispose of diseased red oaks immediately
• Do not transport unseasoned firewood
• Do not store unseasoned oak firewood uncovered
• Late winter or early spring is often deemed the best time for significant pruning work to reduce the risk of infection

If you have healthy oak trees in an area with infected trees, preventative treatment may be effective in slowing transmission. As oak wilt is a systemic, vascular disease, the most effective treatment and only scientifically backed one consists of injecting the infected trees with a fungicidal chemical. The only currently recommended fungicide is Alamo®, a formulation of the fungicide propiconazole. The fungicide is administered through holes drilled in the root flare of the infected tree and should only be applied by Texas Department of Agriculture Licensed Applicators.

For large stands of oak trees, especially live oaks, trenching around the area and severing root connections can limit disease spread, as well.

Can you Treat Oak Wilt?

There is no known cure for oak wilt.  If you have a tree that is infected with oak wilt, be sure to consult a Texas Oak Wilt Qualified arborist or your local Texas A&M Agrilife Extension agent to discuss treatment options.

• Red oaks usually defoliate and die one to six months after becoming symptomatic.
• Live oaks may last up to a few years before total necrosis.
• White oaks show the most resistance to oak wilt and may survive several years after infection.

The only scientifically backed treatment for Oak Wilt is a fungicidal treatment that may prolong the life of infected trees, but cannot eradicate the disease.

However, systemic fungicides are most effective if a tree has not lost more than 30% of the crown. Contact a certified arborist to see if your tree may be a good candidate for treatment.

What Areas Have Oak Wilt?

In North Texas, there are many centers of infection. At Texas Tree Surgeons, we take oak wilt precautions throughout our service area. Still, there are a few neighborhoods in which we have seen particularly bad oak wilt activity:

• Preston Hollow, Dallas
• Lakewood, Dallas
• Walnut Hill and Abrams, Dallas
• Coit and Campbell, Richardson
• President George Bush Turnpike and the Tollway, North Dallas
• Park and US 75 in Plano
• Highland Park
• University Park

If you live in one of these areas, or suspect oak wilt activity in your neighborhood, contact your arborist to see what specific preventative steps are recommended for your trees.

What to Do if There is Oak Wilt Activity in Your Area 

• Protect all trees, and especially oaks, against insects
• Be aware of dead and dying trees and advise neighbors to remove dead wood from their property
• Connect with neighbors to help improve awareness
• If Oak Wilt is within 100 feet of your trees, consider preventative treatments

Oak wilt is one of the greatest threats to trees in Texas, approximately 50% of our urban forest are oaks.

Education, awareness, and prevention are the best tools we have to protect our urban forest from devastation. If you want to learn more about oak wilt, visit TexasOakWilt.org.