Oak wilt is a disease caused by Bretziella fagacearum, a fungus that develops in the xylem, the water-carrying cells of trees. All oaks are susceptible to the fungus, but trees in the red oak group (with pointed leaf tips) often die much faster than the white oak group (rounded leaf tips).
Description
The oak wilt fungus blocks the flow of water and nutrients from the roots to the crown, causing the leaves to wilt and fall off, usually killing the tree. Trees in the red oak group (such as northern red oak, scarlet oak, pin oak, and black oak) can die within a few weeks to six months, and the disease can spread quickly from tree to tree. Trees in the white oak group (such as white oak, bur oak, chestnut oak, and swamp white oak), often take years to die and the disease usually does not spread to additional trees.
Symptoms of oak wilt are often very noticeable in red oaks. In white oaks, symptoms only affect a few branches each year, and progress slowly over multiple years.
Common oak wilt symptoms:
- Leaves suddenly wilt in early July through the end of August, and may fall from the tree while there is still some green on them. Most infected red oaks will lose over half their leaves within a few weeks.
- Brown coloration develops on leaves starting at the outer edge and progressing inward toward the mid-vein of the leaf.
- Branch dieback typically starts at the top of the tree’s canopy and progresses downward.
- Mainly in red oaks:
- Fungal spore mats may develop under the bark of infected trees the spring after the tree dies.
- Dark streaking may be visible in sapwood, the layer of living tissue right below the bark.
Early leaf drop is the most distinctive characteristic of oak wilt. If a tree displays other symptoms, but does not lose its leaves, it most likely does not have oak wilt.
Spread
There are two main ways oak wilt is spread: above ground by beetles and below ground through tree roots.
Spread by Beetles
Fungal spore mats form under the bark of infected red oaks the spring after they have died from the disease. During the warmer months, these spore mats emit a sweet odor that attracts sap-feeding beetles (Nitidulidae) and bark beetles (Scolytinae), which can pick up fungal spores as they crawl around. The beetles are also highly attracted to fresh wounds in trees, including those from pruning. In this way, they spread the fungus from infected trees to healthy trees sometimes miles away. Infected firewood and other wood materials also pose a threat because they can harbor the fungus and/or beetles that can spread the disease.
Spread by Tree Roots
Spread underground occurs when roots of nearby red oaks graft to each other (fuse together), creating a connection through which nutrients and the disease can move. In the Midwest U.S., large blocks of red oak forests have died from the disease in a single season due to their vast network of interconnected roots. In contrast, white oaks are much less likely to create root grafts and spore mats rarely form under their bark, significantly reducing the chance of spread from these trees.
Impacts
Loss of oak trees in New York State would cause economic damage, alter forest ecosystems, and deprive native wildlife of food and shelter. In New York, oak provides $33 million of revenue for private landowners annually. Oak is the second most abundant tree species in NY timberland by sawtimber volume and accounts for 9.4% of the state’s log production. Oak/hickory is the second most abundant forest type in the state, and oak is also a component of the most abundant maple/beech/birch type that occupies over half of New York's forest land. Oaks also produce acorns, a high-value food source for wildlife such as squirrels, turkeys, deer, and bears, and act as a host for many species of caterpillars. Like many other tree species, oaks are also valuable for carbon storage, water filtration, and as landscape trees.
Distribution
History
Oak wilt was first detected in North America in Wisconsin in 1944. The fungus was most likely introduced from Central or South America. Since its initial detection in North America, oak wilt has spread throughout the Midwest and Texas and has killed tens of thousands of trees. Oak wilt was first detected in New York State in 2008. Since oak wilt infections in New York have remained isolated, the disease is not considered to be widespread.
In 2023, oak wilt was found near the Western New York border in Ontario, Canada. To date, no evidence of spread from Canada into New York has been observed. Residents of this area, as well as other areas with oak wilt across the state, are encouraged to watch for oak wilt symptoms and report if seen.
Quarantine Districts
An oak wilt quarantine district is a restricted area put in place around a neighborhood, town or county, after oak wilt is confirmed there. The goal of an oak wilt quarantine district is to prevent the spread of the disease by prohibiting the movement of potentially infected oak wood.
Oak wilt quarantine districts have been established in the towns of Middlesex, Bristol, South Bristol, Italy, and Glenville.
View a map showing current quarantine districts in New York State (PDF).
Prohibited from leaving the quarantine districts:
- Oak logs or branches
- Wood pieces less than 29 inches long, no matter the species
Allowed to leave the quarantine districts:
- Chipped wood
- Wood pieces 29 inches long or greater from trees other than oak.
View the oak wilt quarantine district fact sheet (English version PDF) (Spanish version PDF) for more information.
View the emergency orders that establish Protective Zones and Quarantine Districts around the infections and prohibit the movement of oak and firewood out of the infected areas:
- 2023 Middlesex - Italy Commissioner Order (PDF)
- 2023 Bristol - South Bristol Commissioner Order (PDF)
Management
- During the growing season, DEC conducts aerial surveys and takes samples from oak trees around infection sites to determine the extent of the disease.
- These areas will continue to be monitored for at least five years using aerial and ground surveys.
- Established quarantine districts prohibit the movement of potentially diseased oak wood including firewood.
- DEC is working to eradicate oak wilt in New York State. This includes using different management methods to meet the needs of each infected site.
- At all sites, infected trees are removed and destroyed, and diseased stumps are treated with herbicides.
- Additional methods may include removing nearby oak trees or digging a trench to break root connections between trees, lowering the chance of spreading oak wilt through root grafting.
Most Recent Annual Report
How You Can Help
- Learn to recognize the symptoms of oak wilt, including leaf drop during the summer, leaf discoloration, branch dieback, and fungal spore mats. Check out this helpful video for homeowners: Oak Wilt and the Homeowner.
- Avoid pruning or wounding oak trees in March-September, when spore mats are present and beetles are the most active. If an oak wound occurs during spring or summer, it should be sealed immediately with water-based spray paint or wound dressing. This will slow wound recovery, but also deter beetles from landing on those areas, which will reduce the risk of oak wilt spreading.
- To learn more about the benefits of pruning oaks in the dormant season, read the "Protect Your Oaks" card (PDF) or view DEC's "Winter Pruning for Oak Wilt Detection" video.
- Consider hiring tree care professionals to prune your oaks. Read more about how to select an arborist or tree service.
- If you prune oaks yourself, learn how to do it properly (PDF).
- Arborists and other tree care professionals can read and share our "Protecting Against Oak Wilt: Tips for Tree Care Professionals" booklet (PDF).
- Do not plant oak trees within 150 feet of current or previous oak wilt infections. Learn more about how to plant a tree and choosing the right tree for the right place.
- Follow the NYS firewood regulation, which limits firewood movement to no more than 50 miles, and obey the rules of the Quarantine Districts, which prohibit firewood or oak wood from leaving those areas.
What to Do if You Have Seen Oak Wilt
If you think you have seen signs of oak wilt:
- Take photos of the fallen leaves, the base of the tree, and the whole tree.
- Submit a report through DEC’s Forest Health Reporting Form.
Photos are very important for identifying this disease. DEC staff will analyze the photos and get in touch with you to determine if it is oak wilt. You may also call DEC's Forest Health Information Line at 1-866-640-0652 or email [email protected].
