A view of two pockets of oak wilt treatment areas using the girdle-herbicide treatment, one from the previous year (bottom, yellow circle) and one from the current year (top, blue circle), captured from an airplane. / Photo Credit: Wisconsin DNR

By Alex Hornung, Forest Health Specialist, Plover
Alexandra.Hornung@wisconsin.gov

An aerial survey was conducted in late August over parts of Lincoln and Taylor counties, primarily looking for new oak wilt infection centers.

A rare glimpse of what oak wilt control can look like was captured from the vantage point of the airplane. The photo below shows a girdle-herbicide oak wilt control treatment from this year, with trees dying; and another from last year, with dead trees standing.

When performing oak wilt control work to stop a pocket from spreading, oak trees that are actively wilting and those that are likely root-grafted to the wilting trees are girdled using a chainsaw, with the cuts going into the wood just an inch. Those girdles (cuts) are sprayed with an herbicide to kill the tree and the root system.

A close-up of what the girdle-herbicide method looks like on a tree in an oak wilt pocket. / Photo Credit: Wisconsin DNR

The idea is that the herbicide will be taken in by the roots, both killing the roots and preventing the fungus from moving through the dead root system to nearby trees that have been root-grafted to the wilting trees. The result is often a circular patch of dead trees that rarely is seen from above.

The herbicided trees are left to die for a minimum of a month. Oak wilt is not a decay fungus, so the standing dead trees can be harvested and utilized.

The girdle-herbicide method is one of a few different options woodland owners can use to control oak wilt on their properties. The Wisconsin Department of Natural Resources Forest Health Team has developed an Oak Wilt Management Fact Sheet that details many of the commonly used techniques that are recommended in Wisconsin. For oak wilt diagnostics or questions in woodlots, please reach out to your Forest Health Specialist.