The Lake Where You Live

We’ve seen the beetles decimate the American elms and the emerald borers destroy the ash trees. Now another important tree species is under threat.

Red oaks and pin oaks are essential to the scenery around our lakes and on our properties. And a fungus-carrying beetle is coming for them with a disease called oak wilt. It’s prevalent mostly in the south and central parts of Wisconsin, but pests of this kind have a way of spreading, and oak wilt is slowly marching north. 

On the plus side, oak wilt is easier to prevent than the predations of Dutch elm disease and the ash borers. There are specific guidelines that any of us can follow to help keep the disease in check. But first, a few words about the malady.  

Oak wilt is spread by species of sap-feeding beetles that carry the fungal spores to fresh wounds in the trees. The fungus grows through the water-conducting system (xylem) of the tree, causing it to wilt and die. Fungus mats develop under the bark in fall or spring after the tree succumbs. 

The disease progresses quite rapidly. The symptoms appear from June to September, mostly in July and August, according to the DNR. The leaves of infected trees appear dull green or bronze and fall off while still partly green. The leaves first wilt and drop from the upper canopy, and then the lower leaves follow.   

Prevention is the best remedy; once oak wilt enters a stand of trees, it is difficult to control. The oaks are most at risk in the spring and early summer (April through July), when the spore-carrying insects are abundant and fungal mats are fresh.

A tree is at risk when it is pruned, when a storm breaks off limbs, or when other nearby trees are cut down for harvest. The DNR offers guidelines on harvesting oaks; the specifics depend on the time of year and the location. 

In general, oaks pruned between April and July should be sprayed or painted with a tree wound sealer immediately afterward. This sealer keeps spores from being introduced to the tree’s circulatory system. 

Harvesting should be restricted in the northern part of the state from April 15 to July 15, and in the southern part from April 1 to July 15. The DNR recommends harvesting only outside the restricted period if the stand of oaks is in a county where oak wilt exists or is within six miles of a county with oak wilt. 

In counties that do not have oak wilt and are not within six miles of a county that does, harvest can be considered at any time of year. “However,” the DNR cautions, “it is possible that oak wilt is present in areas where the disease has not been confirmed.” If harvesting during the restricted period, landowners should consider possible impact to adjoining stands.

Oaks are an essential part of the scenic values around our lakes. Although oak wilt may not yet be present where we live, it’s worthwhile to understand the threat and to be well informed and ready to take action. An ounce of prevention truly is worth a pound of cure.

Ted Rulseh, a writer, author and advocate for lake protection, lives on Birch Lake in Oneida County. Visit him and his blog at https://thelakeguy.net.