What is Oak Wilt?
What is Oak Wilt?
At Texas Tree Surgeons, we love trees and we love our customers, and we have created a series of articles covering tree basics. If you have a specific tree question, let us know!
Oak wilt, and the precautions that need to be taken to help prevent the spread of this fungal disease, may be the most often talked-about aspect of tree health care in Texas. Throughout the state, tree owners and communities are challenged by the potential devastation to all species of oak tree. In some areas, there are ordinances in place that restrict oak trimming in order to prevent the spread of the disease. Other areas have no formal regulation, and this can lead to a lack of awareness and a potential for widespread infection.
While oak wilt is a serious threat to our North Texas urban forest, there are simple steps that everyone can take to lessen its impact.
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. For more information on how to submit a sample, see this post or contact your arborist.
Live oak leaves showing the venal necrosis characteristic of oak wilt
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
- Chip or bury all tree material
- Do not transport unseasoned firewood
- Firewood should be dry, splitting, and the bark should be peeling off
- Do not store unseasoned oak firewood uncovered
- Cover tightly with heavy, clear plastic and bury the edges to restrict insect access
- Do not prune or otherwise wound oak trees from February 1 to July 1
- The best time to trim is in the fall and winter
- When infection is a risk, take proper precautions
- Sterilize tools and paint cuts
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 treatments consist 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.
A typical system for fungicidal injection; each green port is inserted into the living tissue of the tree.
Can you cure Oak Wilt?
There is no known cure for oak wilt. Reported home remedies or substances applied to the exterior of the tree have not be proven to have any remedial effect. 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.
Fungicidal treatment 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.
Oak wilt is one of the greatest threats to trees in Texas. 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.
At Texas Tree Surgeons, we love trees and we love our customers, and we believe that the more people learn about their trees, the better we can serve our community. We have several Oak Wilt Qualified arborists on staff; please let us know if you have any questions about oak wilt or any other tree question. We are always happy to help!
This is the contact info for the person actually sending in the form and sample. Make sure to indicate that you are the “Homeowner” or other category at the bottom.
For most tree owners, this will be the same as the Submitter Information. It is extremely important to make sure that the address under this section is where the tree or plant is actually located. An accurate location is essential for disesase tracking.
We recommend receiving results via email, as this is the quickest method. If there is a third party, such as your arborist, to whom you would like the results sent, indicate that here.
This can be one of the most daunting parts of filling out the form. You may not know all the information about your sample. It is important to fill in as much as you do know, so that proper recommendations can be made by the TPDDL.
If you are submitting a sample on your own, you may not have a specific disease in mind, and just want to know what’s wrong with your tree. However, you may have information from an arobirst or other plant health care professional who recommended sample submission. If you are not sure what to select, leave everything blank, and the TPDDL will perform a basic test. If they determine that further testing is required, they will conduct those as well. If you have been instructed by your arborist to get a test for a specific disease, indicate that here.
The TPDDL is supported by state of Texas funds, but does charge a fee for its services. The stardard diagnosis charge (as of December 2018) is $35 per specimen (individual plant/tree). Additional tests carry additional charges (see above). Make sure to include payment for the basic diagnosis and any opther services selected. If further testing is needed, the TPDDL will send a bill for any additional charges. If you do not wish to have any further testing done beyond the basic diagnosis, indicate that in the Comments or on the back of the form. However, an accurate diagnosis and management recommendations may not be possible without more specific tests.
This is the lab-assigned number for each specimen submitted. This number should be used in any correspondence to the TPDDL about your submission.
Here, the TPDDL will confirm the submitter information and provide any general notes about the sample.
long with the dates the sample was received and processed, this section will indicate the TPDDL employeee responsible for your testing (diagnostician) as well as what types of tests were perfomed.
This is the most important section of the lab report. Here, the diagnostician will list one or multiple diagnoses for the problems observed on the samples submitted. This information should be passed on to your arborist.