Oak wilt

What can I do?

 

1. Prevent new infections

Current oak wilt status in Minnesota

The most efficient and cost-effective means of control is prevention. To prevent the introduction of oak wilt, avoid wounding trees during the infection period. Don't prune oaks during April, May, or June!! If at all possible, don't do construction work around oak trees during those months. If work cannot be avoided, carry a can of pruning paint and immediate paint each wound created, including those on exposed roots. Even 15 minutes can mean the difference between prevention and disease.

Further reading about oak wilt protection, prevention, and treatment:

2. Diagnose infected trees

  • Become familiar with the signs of oak wilt and methods for detecting and reporting suspected oak wilt–infected trees. See the USDA Forest Service publicationexternal linkand the University of Minnesota. external link
  • Learn how your community is dealing with the disease. Call your city, township, or county and speak with the tree inspector about possible inspection and treatment programs.
  • If your community does not have an oak wilt program, contact a certified arborist to work with you in managing the disease, or look for disease control under the list of services provided by arborists working in your area.
  • You can also take a sample yourself and send it in for culturing.

3. Control existing infection areas

Vibratory plow

If oak wilt has been diagnosed on your property, a forest pest specialist, forester, or consultant trained in oak wilt management should work with you to assess the need and benefit of root graft interruption before removing infected trees. If there are healthy trees nearby that might share root grafts with an infected tree, vibratory plowing is highly recommended. The machine cuts a narrow, 54-inch-deep slit into the soil to sever the grafts. No soil is excavated from the slit, and site disturbance is usually minimal. No chemicals or barriers are inserted in the slit. This process is a purely a mechanical interruption of interconnected roots.

graphic showing treatment and trencher photograph from Forestry images.org

Removal of diseased wood

To prevent above ground spread, it is important to remove infected trees and properly dispose of the wood. If you want to keep the wood for firewood, follow these steps. All wood from the infected tree that is 4 inches or greater in diameter must be chipped (wood chips from infected trees do not harbor the beetles) burned, debarked, buried, or covered and sealed to the ground with 4-mil plastic sheeting as follows:

  1. Stack or pile infected wood 4 inches in diameter or greater. The size of the pile does not matter, but it should be stable enough to not collapse. Trim branches that may poke holes through the plastic.
  2. Dig a 4-inch deep trench completely around the woodpile.
  3. Completely cover the woodpile with a single sheet of heavy (4 mil or thicker) plastic sheeting (black plastic will absorb heat better, aiding in the process), laying the sheet edges in the trench.
  4. Fill the trench with soil to COMPLETELY SEAL the woodpile from beetles.
  5. Keep the pile sealed until after July 1 of the following year. Then uncover to let the wood finish drying for use during subsequent winters.

Fungicide treatmentphotograph of fungicide from Forestry images.org

Where high-value healthy red oaks occur within the plow line, it may be feasible to inject them with a fungicide to protect them from developing oak wilt. A forest pest specialist, forester, or consultant trained in oak wilt management should work with you to assess the need and benefit of fungicide treatment. Systemic fungicide treatments can also be used to protect high-value red oaks in situations where plow lines cannot be installed. Treating infected red oaks that are already wilting is not recommended and is rarely effective. The fungicide propiconizole is the most widely used product. The chemical is available under several brand names and has been shown to provide disease protection for up to two years. Because the fungicide only stops the fungus from killing the tree and does not prevent root graft infections from occurring, applications may be necessary every two years for continued protection. Fungicides can be effective in preventing and in some cases curing oak wilt in bur and white oaks.

 

4. Replant

Replant with the right tree. Oaks are often found in virtually pure stands. When replanting, be sure to select a species that meets site needs and sustains diversity. For information on selecting trees, check with your city forester. Then see the University of Minnesota Extension external linkinformation for sources of nursey stock in Minnesota.