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1. What is Oak Wilt?

Oak wilt is one of the most destructive tree diseases in the United States. The disease has killed more than 1 million trees in 76 Central Texas counties. Oak wilt is an infectious vascular disease caused by the fungus Bretziella fagacearum. The fungus invades and disables the water conducting system in susceptible trees. All oaks can be infected with oak wilt, but some species of oak are more susceptible than others. Red oaks, particularly Spanish oak (Quercus buckleyi), are very susceptible to the fungus. White oaks, like post oak (Q. stellata) and bur oak (Q. macrocarpa), are resistant to the fungus and rarely die from the disease. Live oaks (Q. virginiana and Q. fusiformis) are intermediate in susceptibility to oak wilt. However, they are seriously impacted by the disease because of their tendency to form root sprouts that result in a vast interconnected root system allowing the disease to easily spread to adjacent trees.

2. Can My Trees Get Oak Wilt?

ALL OAKS CAN BE INFECTED BY THE FUNGUS THAT CAUSES OAK WILT! 

Oak trees in central Texas are placed into one of two groups – red oaks or white oaks. Red oaks are the most susceptible to oak wilt, will typically die within two to four weeks of symptom appearance, and can play a unique role in spreading the disease. Common red oaks in central Texas include: Spanish oak (Quercus buckleyi), Shumard oak (Q. shumardii), and blackjack oak (Q. marilandica).

 

Oaks in the white oak group are the most resistant of the disease, with variations among the group depending on species. Post oak (Q. stellata), bur oak (Q. marilandica), and Mexican white oak (Q. polymorpha) are very resistant of the disease. These species may exhibit some canopy loss, but rarely die when infected. White shin oak (Q. sinuata var. breviloba), chinquapin oak (Q. muehlenbergii), and Lacey oak (Q. laceyi) can grow in stands with interconnected root systems, enabling the fungus to infect adjacent trees. These species are more resistant of the disease than red or live oaks and usually survive infection with moderate to severe canopy loss, but they can die in large numbers from the disease.

 

Live oak (Q. fusiformis) is a member of the white oak group and is the most common and abundant oak in central Texas. While live oaks succumb to oak wilt in the greatest numbers, they are intermediate in susceptibility to the disease with a small percentage (< 20%) surviving infection. Live oaks share a common root system. All live oaks in a stand are likely connected to each other and other live oaks as far as 200 feet away. If oak wilt infects one of the trees in the stand, the disease spreads through the common root system to adjacent trees and an oak wilt infection center begins.

3. Can Oak Wilt Spread?

Oak wilt spreads to other oak trees in two ways – long distances with the aid of certain beetles or locally through common or grafted roots. Sap-feeding (nitidulid) beetles are believed to be responsible for much of the long distance spread of oak wilt. During the spring, the oak wilt fungus forms special spore-producing structures called fungal mats on red oaks.  Nitidulid beetles are small (about 1/8-inch long) and are attracted to oak wilt fungal mats because the mats have a sweet, “fruity” smell. Mats form underneath the bark of diseased red oaks and are not known to occur on live oak trees. The fungal mats apply pressure under the bark causing a tiny crack to form.

 

These mats can be found on the trunk and major branches of red oaks. When a nitidulid beetle feeds on an oak wilt fungal mat, spores of the oak wilt fungus will cling to the body of the beetle. Nitidulid beetles also feed on tree sap associated with fresh wounds. If a beetle contaminated with oak wilt spores lands on a fresh wound on a healthy oak, then that tree can become infected. Tree wounds can be made by man or nature, but nitidulid beetles are attracted to both.

 

Once established, the fungus moves from one tree to the next through common or grafted roots.

4. How Can I Prevent My Trees From Getting Oak Wilt?

Prevention plays an important role in the management of oak wilt. Landowners and homeowners can take an active role in oak wilt prevention by taking the following steps:

1. Avoid pruning or wounding oaks between February 1 and July 1. This is the time of year when oak wilt fungal mats are most likely to form and nitidulid beetles are active. If a nitidulid beetle carries oak wilt spores from a fungal mat to a fresh wound on an uninfected oak tree, the fungus could become established in the disease-free tree. The least hazardous periods for pruning are during the coldest days of midwinter or extended periods of hot weather in mid- to late summer.
2. Sterilize/Sanitize all pruning equipment between trees using denatured methyl alcohol (shellac thinner), isopropyl alcohol, or a general purpose household disinfectant such as Lysol, Listerine, Pine-Sol or related products. Using household bleach is NOT recommended as it can be corrosive to pruning tools as well as people.
3. Immediately paint all wounds on oaks to prevent contact with contaminated beetles. Wounds should be painted, regardless of the time of year they were made, with commercial tree wound dressing or latex paint (color doesn’t matter!). Wounds can be either man made or natural and include freshly-cut stumps and damaged surface roots.
4. Do not transport or buy unseasoned firewood. Fungal mats may form on unseasoned red oak firewood infected with oak wilt making it possible to spread oak wilt to uninfected areas. Seasoned firewood (dried for at least one year) should not present a threat of spreading oak wilt. Also, burning infected wood cannot transmit oak wilt.
5. Promptly remove and either burn or bury all red oaks that are dying or have been recently killed by oak wilt. Generally, this would be oak wilt-infected red oaks that die in the late summer or fall. This will prevent nitidulid beetles from spreading spores from fungal mats that may form on the trees in the fall or the following spring.

5. Does The City Have Cases of Oak Wilt Within City Limits?

Yes, the City has experienced cases of oak wilt within City limits.

6. Can Residents Receive Financial Assistance For Oak Wilt Abatement?

The City created a program to partially reimburse homeowners with oak wilt abatement expenses.

7. How Can I Help With Oak Wilt Abatement?

The City is encouraging residents to donate to the Oak Wilt Fund at First United Bank to help residents offset some of the oak wilt abatement costs.  If oak wilt spreads throughout the City, it will affect our beautiful trees and property values. 

8. Where Can I Learn More About Oak Wilt?

There are education materials on the City website and at City Hall to help with identifying oak wilt and some precautions you can take to avoid oak wilt damage.

More about the Oak Wilt in Texas and the Texas Oak Wilt Suppression Project:

• Read more about the oakwilt suppression project of 2013 (PDF, 9MB).
• Download an information sheet about identification and management of oak wilt (PDF, 654 KB)
• Visit the Oak Wilt Partnership website at http://texasoakwilt.org/