Obits
Wisconsin Tree Disease Alert: Oak Wilt Confirmed in New Areas
Madison, WI – A destructive tree disease continues to threaten Wisconsin's oak population, with newly documented oak wilt detections in 2026 highlighting concerns about the disease's spread and the im
By Erin Vale · 2026-11-05T19:53:33.917Z
Madison, WI – A destructive tree disease continues to threaten Wisconsin's oak population, with newly documented oak wilt detections in 2026 highlighting concerns about the disease's spread and the importance of protecting healthy trees.
According to the Wisconsin Department of Natural Resources, an updated oak wilt detection map dated October 21, 2026, identifies new confirmed locations this year, alongside areas where the disease has already become established.
The map shows new detections in portions of northern and eastern Wisconsin, including areas around Oneida and Manitowoc counties.
Disease Can Kill Oak Trees and Spread Underground Oak wilt is a serious fungal disease that disrupts a tree's ability to transport water, potentially causing rapid decline and death.
The DNR explains that symptoms are often most noticeable during mid to late summer, when infected trees prematurely shed leaves or branches begin wilting.
Affected leaves frequently display a distinctive combination of green and bronze or brown coloring.
Once a tree becomes infected, the disease can spread to nearby oaks through connected underground root systems.
Over longer distances, beetles can carry the fungus to fresh wounds on otherwise healthy trees.
Wisconsin Residents Urged to Protect Oak Trees The DNR recommends avoiding oak tree pruning or unnecessary injuries from April through July, when the risk of infection is highest.
If an oak must be cut or becomes damaged during that period, exposed wounds should immediately be covered with a water based latex paint or pruning sealant.
Residents should also avoid transporting oak firewood long distances, keeping it near where it was cut for at least one year or until the bark naturally loosens.
Although treating underground spread can be difficult and expensive, early prevention remains an important way to protect Wisconsin's oak trees.
Residents noticing unusual leaf browning or premature leaf loss should seek guidance from a qualified tree professional or the Wisconsin DNR.