Oak Wilt: Harvest Guidelines for Reducing the Risk of Introduction and Spread in a Forest Setting¹

This guide is designed to provide information for landowners, managers and loggers on the relationship between the risk of introduction of oak wilt (caused by the fungus Ceratocystis fagacearum) and the timing of any activities that may wound oaks or leave oak stumps. This guide also provides information on the relationship between various site and stand factors and the expected level of disease impact (based on root-graft spread). Information on the biology and management of oak wilt may be found in UW Extension Publication # G3590, Oak Wilt Management: what are the options?(exit DNR).

When should I use this guide?

• When your management plan includes retaining oak as part of the timber type
• AND, When your oak type includes any of the following red oak-group species (northern red, Quercus rubra; black, Q. velutina; and northern pin oak, Q. ellipsoidalis) alone or mixed with white oak-group species (white oak, Q. alba; bur, Q. macrocarpa; and swamp white oak , Q. bicolor). The risk of spread will decrease as the component of white oak-group trees increases because root grafting is rare between white and red oaks.
  

Am I required to use this guide?

• If your property is part of the Managed Forest Law (MFL) program, the guide should be used to help make decisions about when harvesting may occur. Other factors that influence the timing of harvest (such as site factors, soil moisture) that are not related to oak wilt must also be considered.
• If you desire to follow generally accepted practices that minimize the impact and risk of introducing oak wilt, you should follow the guide.

When is it not necessary to use this guide?

• If you are converting to a non-oak type or if oak is not considered to be an important part of the stand’s future.
• Consideration:
  If you choose not to use the guide or if you make decisions that could introduce oak wilt, be aware of the potential impact of introducing oak wilt from your property onto adjacent properties through root-graft transmission.

If I follow this guide, will all risk of introduction and spread be eliminated?

• It is impossible to eliminate all risk of introducing oak wilt into a forest stand. Use of this guide is not intended to eliminate risk but to provide information on the levels of risk of introduction and spread so you may make informed decisions to greatly reduce risk.

What forms the scientific basis of this guide?

• Climate data and research on vector activity and fungal mat formation have shown that the risk for overland spread through fresh wounds increases significantly around April 1 south of the tension zone and April 15 north of the tension zone. The risk of overland infection decreases significantly after July 15 statewide. A three-year study (2006-2008) is examining the risk of introduction July 15 - October 15. Data from this study will provide further information related risk during the summer and early fall.
• Additional research has shown that root grafts, which facilitate underground spread, are more common in light textured soils and less common in heavy soils. Observations in varying terrain has revealed that root grafts are more common in areas that are flat or rolling (0-12% slope) and less common in terrain that has steep hills and deep valleys (>12% slope).

Under what circumstances might it be appropriate to vary from the guidelines?

• Your stand is in an area where oak wilt is rare and locations are well documented (contact your DNR regional forest health specialist for location information). If there is no oak wilt within 6 miles of your stand, and you wish to harvest oak during the high risk time period, the risk of introduction will be reduced, thus cutting during high risk time periods (April 1 (south) or April 15 (north) to July 15) may be acceptable. In general, oak wilt is so common in the southern two-thirds of Wisconsin that it would be unusual to have an area that is oak-wilt free for 6 miles in all directions.
• If multiple forest health issues are affecting your stand and unusual circumstances prohibit harvesting during low-risk time periods, varying from the guidelines may be appropriate.

What should I do if I want to vary from the guidelines?

• If the land with the stand is enrolled in the managed forest law (MFL) program, county forestry program or is state land: 1) Contact your regional forest health specialist to discuss whether or not varying from the guidelines is appropriate and 2) If determined to be appropriate by the DNR Regional forest health specialist, document justification for varying from the guidelines and include the documentation or a reference to it into your normal approval process for harvesting i.e. on form 2460-001 (timber sale and cutting report) for public lands and on form 2450-032 (cutting notice) for MFL lands. Documentation is the responsibility of the landowner.

How does the “stump treatment” option work?

Apply tree wound dressing to the last 3 growth rings.

• Treatment of stumps is recommended as an option only for stands that have a basal area of oak <15 square feet/acre, if you are cutting in the spring and are in a county with oak wilt. To treat stumps apply a tree wound dressing product (available at most hardware stores) to the last 3 growth rings. Only one treatment is necessary but this must be done each day to the stumps that were created that same day.

Are there other ways I can minimize the overland spread of oak wilt?

• Yes. Trees that wilt during the summer and early fall will produce small mats of the fungus under the bark the following spring and early summer. If you are moving oak firewood or logs that were killed by oak wilt, utilizing the material [see Dealing with Diseased Wood] before April 1 will minimize the risk of the fungus spreading overland via sap-feeding beetles. Wood is no longer infectious once the bark has fallen off.

¹Dr. Jennifer Juzwik, USDA Forest Service research scientist led this team effort. The team included consulting, industrial, county and DNR foresters, forest health specialists and a forest ecologist.