Oak wilt is a fungal disease that kills thousands of oak trees annually. Oak wilt spreads in two ways: through root grafts between similar species, radiating outward from a centrally infected tree; and over land, by oak sap beetles carrying fungal spores from tree to tree.
The oak wilt status system uses three "risk" description periods: High Risk, Low Risk and Safe.
- High Risk – usually occurs during April, May, and June.
- Low Risk – typically occurs during July, August, September, and October
- Safe or No Risk – November, December, January, February, and March.
Management activities including pruning and tree removal should be avoided during High and Low risk periods to minimize the spread of oak wilt to susceptible trees. Click link below to confirm the current oak wilt status.
These three probabilities of risk are based on the following:
- First, is the fungus that actually causes the disease active?
- Second, is the beetle that carries the fungus to the oak tree active?
- Third, is there oak wilt disease in the area?
If all three criteria are met, then the transmission of oak wilt from one area to another is very likely.
For additional oak wilt resources and information, visit the websites below:
The overland spread of oak wilt can be controlled by avoiding wounding or pruning oaks from April – October. If trees are accidentally wounded or pruning is unavoidable, cover the wounds immediately (within minutes) with a non-toxic wound dressing. Remember: The only safe period for pruning oak trees is from November – March.
Please do not move logs or firewood from recently wilted oak trees to areas where oak wilt is not present. Oak wilt spore mats may form on these logs. Long distance movement of firewood has resulted in the establishment of oak wilt in distant areas that previously had been unaffected by the disease.
Oak wilt management activities may include the following:
Macro-Injection of a Fungicide – Injecting a fungicide into adjacent, healthy, “at-risk,” red oak or currently infected white and bur oak trees.
A licensed tree contractor hired by the homeowner will inject the fungicide propiconazole below-grade via the macro-infusion process into the root flares of healthy red oaks that are “at-risk” for infection. This process can also be used therapeutically to save white and bur oaks that are currently infected with oak wilt.
Mechanical Root Graft Disruption – Severing grafted root systems to prevent the underground spread of the oak wilt fungus.
To slow the underground spread of oak wilt disease on flat terrain, a qualified, licensed contractor hired by the homeowner will use a vibratory plow or trencher to sever the grafted roots of oak trees. The root graft cuts must be five feet deep for effective control. Barriers must be installed in accordance with the approved Minnesota DNR guidelines.
Potential Spore Producer (PSP) Tree Removal and Disposal – Removal, proper disposal and stump-grinding of PSP red oak trees.
The City of Eagan Forestry Staff will re-inspect the oak wilt infected red oak trees in late November. The red oak trees that are PSP trees are identified and clearly marked with a painted yellow “X” on the trunk. Property owners are notified via mail the PSP status of their infected red oak tree(s). The only oak wilt infected trees that are required to be removed by the City are those determined to be PSP trees. Not all red oaks are PSP trees. PSP trees are required to be removed by next February 15th. The City of Eagan does not require the removal of non-PSP trees.
These expenses incurred by the homeowner are eligible for reimbursement. All oak wilt management expenses require the use a City of Eagan licensed tree contractor. Access the list of licensed tree contractors.
If an oak wilt infected tree is identified
If the City of Eagan Forestry staff identifies oak wilt-infected trees on your property, the trees will be clearly marked and numbered with yellow paint. An oak wilt notification packet will be mailed to you containing the following documents:
- An official Notification Letter
- An aerial photograph identifying the location of the infected tree(s) on the property
- A copy of Eagan City Code 10.20 – "Shade Tree Disease Control and Prevention"
- A copy Minnesota Statute 18G.13 – "Local Pest Control"
Removing Infectious Oaks
Red oak trees infected with oak wilt this year may spread the oak wilt fungus overland to adjacent, vulnerable red oaks next spring. These trees have the potential to produce spore mats that contain oak wilt fungal spores. Sap beetles visit the spore mats and transport the fungus to adjacent trees. A tree that has the potential to produce spore mats is called a potential spore producer (PSP). Not all oak wilt infected red oaks are PSP trees. A standing PSP tree or uncovered wood, in a woodpile from a felled PSP tree, poses a threat to adjacent, healthy, red oaks next spring. All red oaks that were marked with a number and a yellow ring, June – September, will be re-inspected in late November by City of Eagan Forestry staff to determine the PSP status.
Proper disposal of a PSP tree:
- Cut the entire tree down in late autumn or winter leaving no more than a 2 – 4-inch high stump.
- All wood from the PSP oak tree must be promptly transported to an approved wood waste use site, kiln-dried or processed into lumber. The homeowner may burn infected wood on site. If the firewood is not used by the following spring, it must be completely covered and sealed to the ground with 4 – 6-mil thick plastic sheeting until the end of September of the following year while being stored on site.
The following steps are recommended for covering infected wood:
- Stack or pile all infected wood 3 inches in diameter or greater. The size of the pile does not matter, but it should be stable and not collapse. Trim branches that may poke holes through the plastic.
- Dig a 4-inch deep trench completely around the woodpile. If you cut down the tree and cover the wood during winter months, when the ground is frozen, seal the plastic to the ground by piling heavy objects around the base of the pile, then return when the ground is thawed to dig a trench and bury the plastic into the ground.
- Cover the woodpile completely with a single sheet of heavy (4 mil or thicker) plastic sheeting and lay the sheet edges in the trench. (Clear plastic is preferable.)
- Fill the trench with soil to COMPLETELY SEAL the woodpile.
- Keep the woodpile sealed until the end of September of the following year. At that time you may uncover the wood to complete drying.
Oak Wilt Management Activities Reimbursement
The City of Eagan offers monetary incentives to residents to control and slow the spread of Oak Wilt disease on private property. The availability of funds is limited and will be dispersed in the order in which management activity invoices are received.
Reimbursement Request Procedure
Residents should submit a copy of a paid, itemized, invoice for any or all of the Oak Wilt management activities covered in the cost-share program to the City of Eagan Forestry Staff as soon as possible following the completion of the activity.
Submit by mail or e-mail to:
3501 Coachman Point
Eagan, MN 55122
We encourage you to contact us with questions or comments by e-mail to the
Licensed Tree Contractors
We encourage residents to hire licensed tree contractors to safely remove and dispose oak wilt infected tress and debris. Visit the Licensed Tree Contractor page listing companies offering these services.