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Last Chance to Prune Oaks

M. Grabowski, UMN Extension Educator

Fresh pruning cuts on an oak tree.
M.Grabowski, UMN Extension 
If you have oaks in your landscape that need pruning and you live in an area of Minnesota where oak wilt occurs, pruning must be done before the oak wilt fungus and it's insect vector become active. Oak wilt is a fatal disease of oak trees that can be found in some counties of Minnesota. If you live in an area where oak wilt occurs, it is critical to prune oak trees before the high risk infection period begins in April. The risk status for oak wilt is updated as weather conditions change, but in a normal year high risk of oak wilt infection occurs in April, May, and June. Check in with My MN Woods to find the current oak wilt risk status before you prune.

Oak wilt has been found within
20 miles of all areas colored pink
MN DNR 
Oak wilt is caused by a fungal plant pathogen. Spores of the oak wilt fungus are carried by sap feeding beetles in the Nitidulidae family. These small beetles are attracted to wounds and fresh cuts on oak trees. When they arrive at the cut branch, spores of the oak wilt fungus are knocked off and can infect the open wound.

Red oak trees are highly susceptible to oak wilt and can wilt and die in as little as 4 weeks after infection. Once infected with oak wilt, there is no way to save a red oak tree. White and bur oaks can also become infected with oak wilt. These trees are able to slow the infection but will eventually succumb to the disease in a few years. Some treatment options are available for white and bur oak trees if the disease is identified at the early stages.

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