Click below to listen to my 2 min. Garden Bite radio show: Oak wilt
Last year, a friend of mine had, what used to be, a gorgeous old oak tree. Sadly it developed Oak wilt. It won’t survive. Oak Wilt is caused by a non-native, invasive fungus Ceratocystis fagacearum. (now you know why I didn’t even try to pronounce it on my radio show!)
And now, Oak will has traveled further north, for the first time showing up in Crow Wing County, Minnesota. Wisconsin also has the disease.
Oak wilt fungus deprives the tree of water. The fungus isn’t visible, but the symptoms are obvious: the tree’s leaves wilt from lack of water and die.
As the disease advances – sometimes quickly – the whole tree, or a cluster of trees, will show symptoms and begin to die.
While the oak wilt pathogen can infect all species of oak, those in the red oak group (leaves with pointed lobes) die about two months after infections. Bur oaks die between one and seven years after infection, while white oaks die anywhere from one to over 20 years.
Oak wilt infection spreads in two ways: above ground by sap beetles, and below ground through roots that have grown together, called root grafts.
The sap beetles are why we do NOT prune oak from April to July, even safer, into October.
THIS year, with drought, it’s even more important not to prune. The pruning attracts the beetle. Wisconsin is seeing it in about three quarters of the state.
Wilting usually starts at the top or outer portions of the tree crown and quickly progresses downward.
Resources:
Oak Wilt in MN [UofMN] There is a LOT of great info here on this site.
Oak Wilt [MN DNR]
Oak wilt [USDA]
Oak wilt was first discovered in Minnesota around 1950. Today oak wilt is widespread in the southern half of Minnesota and continues to expand its range northward. To date, oak wilt covers about one-third of the area where Minnesota oaks grow.
If you suspect your oak has oak wilt, get a professional opinion before doing any kind of possible treatment. Hire an experienced tree care professional or consult the University of Minnesota’s Plant Disease Clinic.
Note: there have been “some” confirmations of oak wilt in western South Dakota.
