Power of Prevention: Oak Wilt

Sarah Topp Sarah Topp
Of all the trees in the Midwest, red oak species are the most significant to me. Their sturdy limbs have provided many sanctuaries for me; whether it was the perfect hiding spot while playing hide-and-seek with my siblings as a kid, the rope swing I took my first plunge into the inviting waters of a Northern Michigan sinkhole lake from, or the spot I eagerly waited for that big trophy buck each early bow season. However, due to oak wilt, my very favorite tree species is at risk!
Red oak leaves showing oak wilt symptoms Red oak leaves showing oak wilt symptoms
Oak wilt is a tree disease caused by a fungus that plugs the water-conducting system of oak trees. To block the spread of the fungus, the trees produce gums and resins which further plug the system, causing infected trees to die within just a couple of weeks. Oak wilt is mainly a problem of red oak varieties including northern red oak, black oak, and pin oak. White oaks can be infected also, but are more resistant and the disease progresses more slowly.
A critical period for oak wilt susceptibility in red oak trees is between April 15th and July 15th. Wounding trees may be accidental (lawnmowers, disc golf, etc.) or intentional (pruning). Sap-feeding insects are only attracted to the sap exposed from wounds several hours after occurrence, but the beetles are numerous and widespread during this critical period creating a high risk of oak wilt.
Oak wilt fungus fruiting bodies under bark Oak wilt fungus; fruiting bodies under bark
Like most diseases, prevention of oak wilt is much easier than elimination once it becomes established. It’s easy; don’t injure or prune trees between mid-April and mid-July!! Oak wilt spreads by passing through root grafts to adjacent healthy trees. The fungus can also be carried to new areas by sap-feeding beetles that move spores from infected trees to freshly wounded healthy trees. It can also be moved in firewood, forming spore-producing pads under the bark which attracts the sap-feeding beetles and they will then move the spores up to several miles away. Attempts to control the spread of oak wilt can be made, but are complex and expensive in practice, utilizing large plow equipment and pesticides. The trick is to stop the movement of the fungus by severing root grafts between healthy and infected trees. Simply removing the infected tree without severing the root grafts first is not effective because the fungus can still thrive in the root system and spread; the infection process can actually speed up as a result.
I’m not the only one that holds these trees to such high value. Northern red oak provides good cover and nesting sites (including cavities) for a wide variety of birds and mammals. Deer, elk, moose, and rabbits commonly browse the leaves and acorns produced as well as the young seedlings of these trees. You can help prevent this disease from expanding to keep our wildlife habitat abundant with these essential mast producing trees!

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