Oak wilt, a lethal disease of oak trees, is spreading in our town.
The Town of Washington now has thirteen confirmed cases of oak wilt – a devastating disease, killing trees rapidly in a single season. There probably are unreported cases, but these are the ones the DNR has documented.
Linda Williams, WDNR Forest Health Specialist, commented that last year was a “big” year for new oak wilt infections in Vilas County because of the spring storms that broke branches. Oak wilt continues to increase in Vilas County.
According to Ted Foley, a certified arborist with Foley Tree Service, there are certainly more than this number of cases, and it will continue to spread and get worse. He stated oak wilt is becoming very prevalent.
Oak wilt is a fatal fungal disease that causes wilting and eventual death of oak trees.
Trees are initially infected by sap-feeding beetles. Wounds created by storms or pruning serve as a feeding site for these beetles and as an entry point for the fungus. The beetles pick up fungal spores from infected trees, then fly to healthy oaks to feed on sap flowing from fresh wounds, thus infecting new trees.
Once the tree has been infected, the fungus moves through grafted roots to healthy trees nearby. In this way, the disease will kill more and more oaks each year if it is not stopped. As the tree dies, the fungus reproduces. The fruity smell of fungal mats attracts beetles, which carry fungal spores to fresh wounds.
Any injury or wounding to an oak tree can leave it vulnerable to oak wilt, whether it be storm damage, pruning, or trimming. Wounding includes not only areas where bark is scraped/scuffed off, but also broken branches, and even root damage can be an entry point for oak wilt.
Oak wilt also spreads when firewood or logs from infected trees with fungal mats are moved.
Initially, single branches on infected trees wilt and die. Leaves on these branches often turn tan or dull green, starting at the tips or outer margins. Leaves may also droop, curl, or fall from the tree. Infected trees die. OAK WILT CAN KILL OAKS IN LESS THAN ONE MONTH.
To prevent infection, avoid wounding trees from April 15 through July 15 when beetles are active. Best to prune when trees are dormant.
If trees are wounded during these months, prevent beetles from interacting with fresh wounds by applying water-based wound sealer immediately.
Fungicides have been developed that may be effective in preventing oak wilt when injected into living oak trees without active symptoms. A single treatment can protect red oaks from developing symptoms for 2 years following injection. Treatment is less expensive than removing a dead tree!
For help with identifying, preventing, and managing oak wilt infections, contact WDNR Forest Health Specialist, Linda Williams, at Linda.Williams@wisconsin.gov or a certified arborist
