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 the red oak group (with pointed leaf tips) often die much faster than white oaks (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. Red oaks (scarlet oak, pin oak, black oak, etc.) can die within a few weeks to six months, and the disease spreads quickly from tree to tree. White oaks (bur oak, chestnut oak, etc.), often take years to die and the disease usually cannot spread to additional trees.
Symptoms of oak wilt infection are often very noticeable in red oak species, but aren't easily seen in white oaks.
- Brown coloration develops on leaves starting at the outer edge and progressing inward toward the mid-vein of the leaf.
- Branch dieback starts at the top of the tree's canopy and progresses downward.
- Leaves suddenly wilt in the spring and summer and individuals may fall from the tree, typically while there is still some green on them. Most infected trees will lose over half of their leaves.
- Fungal spore mats may develop under the bark of infected trees after the tree dies.
Distribution and Habitat
History
Oak wilt was first discovered in Wisconsin in 1944, but where it originated is still unknown. It has spread throughout the Midwest and Texas and has killed tens of thousands of trees in the U.S. However, in New York State, oak wilt infections have been isolated to smaller trees and is not widespread. Oak wilt was first in New York in 2008.
Impacts
In New York, oak is associated with $55 million of revenue for private landowners annually. Oak is the fourth most abundant tree species in NY timberland by sawtimber volume and has increased by over 20% since 2007. 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 NY's forest land. Oaks are valuable as landscape trees, for carbon storage, for water quality, and as a mast-producing species for wildlife such as squirrels, turkeys, and deer.
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 just under the bark of infected red oaks after they have died from the disease. During the warmer months, these spore mats emit a sweet odor that attracts sap-feeding beetles and bark beetles, which can pick up fungal spores as they crawl around. The beetles are also highly attracted to fresh wounds in other trees-often caused by 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, 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.
Quarantine Districts
An oak wilt quarantine district is a quarantine 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 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 attempting to eradicate the disease in Middlesex, South Bristol, Canandaigua, Brooklyn, and Glenville using methods similar to those originally used in Glenville.
- Oak-free zones will be established where infected and surrounding oak trees will be removed.
- Where possible, root disruption will be used to break root connections to lower the chance of spread.
- In Suffolk County, DEC will only attempt to contain the disease due to the number of infection sites and distribution across Long Island. Only infected trees will be removed. To ensure that infected trees do not continue to spread the disease, they will be chipped and incinerated.
Management Plans
Most Recent Annual Report
Future Oak Plantings
Oak should not be planted within 150 feet of known oak wilt infections. DEC recommends planting a variety of tree types. Oaks are an important part of community forests, and they should be planted when site conditions are suitable for them. Learn more about how to plant a tree and choosing the right tree for the right site.
How You Can Help
- Learn to recognize the symptoms of oak wilt including 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 the spring and summer, 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) Use tree care professionals. Read more about how to select an arborist or tree service.
- Arborists and other tree care professionals can read and share our "Protecting Against Oak Wilt: Tips for Tree Care Professionals" booklet (PDF).
- If you prune, learn how to do it properly (PDF).
- View DEC's "Winter Pruning for Oak Wilt Detection" video to learn how to help prevent the spread of oak wilt.
- Follow the NYS firewood regulation which limits firewood movement to no more than 50 miles and obey the rules of the Quarantine Districts, which prevent firewood or oak wood from leaving those areas.
What to Do if You Have Seen Oak Wilt
After reviewing the identification material on this website, if you think you have seen signs of oak wilt:
- Take photos of the symptoms, as well as the tree's leaves, bark, and the entire tree.
- Email photos and location information to us at [email protected].
DEC staff will analyze the photos and get in touch with you to determine if it is oak wilt. Photos are very important for identifying this disease. You may also call DEC's Forest Health information line at 1-866-640-0652.
Additional Resources
- Arborists and other tree care professionals can read and share our "Protecting Against Oak Wilt: Tips for Tree Care Professionals" booklet (PDF).
- View DEC's "Winter Pruning for Oak Wilt Detection" video to learn how to help prevent the spread of oak wilt.
- How to Identify, Prevent and Control Oak Wilt (PDF) - a US Forest Service publication
- View DEC's Nitidulidae: Sap-Feeding Beetles poster (PDF)
