Oak Wilt Update

Trees rarely make headline news. When they finally do, it can inspire action and lead to positive outcomes.

In October 2025, the Milwaukee Journal Sentinel reported Oak wilt had been confirmed in Whitnall Park. The story struck a nerve across Southeastern Wisconsin. Many residents began paying attention to their trees and searching for resources. This response reveals how deeply our natural heritage compels us to protect trees and forests.

Milwaukee County Parks acted quickly. Nearly 30 Oaks were removed after showing symptoms of Oak wilt. Oak wilt rapidly kills trees by blocking water flow, spreads through root grafts, and requires complete removal plus trenching to prevent infection of nearby trees. This work is costly and difficult. Still, the alternative—a world without mature oaks—is unacceptable.
Oak wilt has spread across Wisconsin since the 1940s. The disease can be devastating for tree owners and arborists. Here are some of the biggest challenges:

• Detection is tricky. False negatives are common since isolating the fungus from dying branches is difficult, so visual symptoms must also be considered alongside lab tests.
• Fungus can survive in wood for years; infected wood should be split and tarped quickly to stop spore spread.
• Information on how Oak wilt transfers to regenerated stands of Oak after removal is limited, making long term re-growth plans largely experimental.
While much about the disease remains uncertain, this much is known:
• Oak wilt can be spread two ways: through root grafts underground and sap-feeding beetles drawn to fresh wounds.
• A mature Red oak can die within a month of infection.
• Outbreaks are increasing, especially in Southern Wisconsin.
• Warmer springs are shifting the infection window.
• Preventative fungicide injections are effective against root graft transmission, but not once infection is established.
• Nearby Oaks of the same species can be infected through root system connections below ground. Cutting these connections is often the first step to protecting healthy oaks from infected trees.

Most tree owners choose preventative trunk injections of propiconazole every 2–years for 6–9 years. This option is not for every tree but should be discussed with your Wachtel Tree Science arborist.

Technology is also advancing. The University of Wisconsin–Madison Extension created a thermal mapping system. This online tool helps foresters, municipalities, arborists, and homeowners assess risk based on date and location.

I remain hopeful that more tools and management methods will emerge to protect our Oaks. Continued reporting from the DNR, Journal Sentinel, and other outlets will be vital. Public awareness and action are our strongest defense against Oak wilt.