Planning & Zoning Administration
Forestry & Trees - Recommended Tree Species
If oak wilt is suspected, call 763-241-1170, Extension 3, for more information or to schedule an on-site inspection.
If oak wilt is diagnosed, landowners are encouraged to consider available options to control spread of disease such as oak wilt suppression work including vibratory plowing (severing the roots), infectious tree removal, and fungicide injections.
What is Oak Wilt?
Oak Wilt is a fungus that affects the vascular (water conducting) system of a tree. As the fungus enters the tree, the gums and resins produced by the tree plug the vascular system in an attempt to stop the fungus. With the vascular system being plugged, the tree wilts due to a lack of available moisture. Oak Wilt is the number one shade tree disease in Minnesota and kills thousands of Oak annually in Sherburne County alone.
How is Oak Wilt Diagnosed?
Oak Wilt affects all species of Oak in Minnesota. Red Oak and Northern Pin Oak are most susceptible with Bur Oak and White Oak being less susceptible. Once infected, a Northern Pin Oak can die in as few as seven days. An infected Bur Oak may die very quickly, or over a period of several years.
Symptoms to look for:
 | 1. Rapid premature leaf drop |
 | 2. Browning leaves from the outer margins of the tree |
| 3. Rapid browning of the crown from the top-down | |
 | 4. Stained wood in the vascular system |
 | 5. History of dying Oak in a circular pattern |
How is Oak Wilt Spread?
Oak Wilt is spread in two ways. The most common method of spread is through grafted or inter-connected roots between healthy and diseased trees. Roots from mature trees will typically extend out 50 feet or more.
Oak Wilt is also spread by insects called picnic beetles. Picnic beetles are fairly common and are attracted to sweet smelling odors. Trees that have recently died from Oak Wilt produce a spore that emits a citrus-like odor. When beetles feed on the fungus from the spore mat, and then travel to the fresh sap of a recently wounded tree, the Oak Wilt fungus can be carried on their bodies from a diseased firewood pile to a freshly injured tree.
Suppression of Oak Wilt
Oak Wilt Suppression involves two equally important steps.
- Severing the roots between healthy trees and diseased trees to isolate fungus
- Removing, disposing of, and/or treating diseased wood in a timely manner
Treatment recommendations and management strategies
- Do not cut actively wilting trees down until roots are severed--it may accelerate fungus growth
- Chipping, burning, or covering diseased wood by April 1st of the the Spring after they have died
- Splitting the wood immediately after they have died to allow wood to dry during the summer heat
- After root cutting work, remove all live trees within the primary control line (cut-to-the-line)
- An injection treatment for Oak Wilt is available.
- Consider a management or restoration plan in large acreage Oak Wilt sites
How can Oak Wilt be prevented?
Prune Oak trees only at recommended times
- High risk dates:
- No pruning is recommended between April 1 thru July1
- Cover all wounds immediately with tree paint
- Risk is greatest within 1/4 mile of active Oak Wilt sites
- Low risk dates:
- July thru October
- Covering wounds is optional
- Risks of infection is dependent on conditions
- Safe dates:
- November through March
- Covering wounds is not necessary
- This is the ideal time to prune Oak
Other Suggestions
- Install tree fencing around trees near construction sites
- Avoid exposing wounded roots when installing decks, septic system, wells and foundations
- Inform anyone who will be working around trees on your property during critical infection times (April thru July)
Sherburne County Govt Center
ATTN: Zoning Administration
13880 Business Center Dr NW
Elk River, MN 55330-1692
Office Location & Hours
| Phone: | 763-765-4450 800-438-0578 |
| Fax: | 763-765-4467 |
zoning@co.sherburne.mn.us