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Protect our trees by holding off on pruning oaks
Published: 4/28/2020
Novi residents can help protect the City’s trees from the deadly oak wilt disease by simply holding off on pruning oaks until late fall or winter.

Oak wilt is an exotic vascular disease which can quickly kill otherwise healthy oak trees — within just a matter of weeks. The disease is caused by a fungus, Bretziella fagacearum, which clogs the water-conducting vessels of oak trees causing them to wilt and eventually die.

The fungus is spread in two ways: overland by sap beetles that carry fungal spores on their bodies and underground through the interconnected root systems of multiple oak trees. Because roots from different trees often times graft into one another, a single infected tree can infect an entire forest of interconnected oaks.

Novi property owners can unknowingly spread oak wilt to healthy trees. By pruning oak trees, people are inducing wounds on the tree. When that pruning occurs during the sap beetles’ active season from March to October, the insects are attracted to the fresh wounds while oak wilt fungal spores hitch a ride on their backs, thus infecting the tree. Moving diseased firewood or other woody debris also helps oak wilt spread.

The Michigan DNR recommends that individuals not prune oak trees at all from April 15 – July 15 and to limit pruning of oak trees unless absolutely necessary through the rest of the growing season in spring, summer and early fall. However, these ranges are only approximations and do vary based on weather conditions. If oak trees must be pruned during elevated risk periods, the wounds should immediately be painted with tree wound paint or latex paint. If oaks must be removed during the elevated risk period the stumps should also be immediately ground.

As the name implies, oak wilt symptoms may manifest as leaves wilting or dropping off the tree rapidly during the summer. Discoloration and wilting generally start at the top of the tree first, and then quickly move downward as leaves bronze and then rapidly fall from the tree out of season. Species in both the red oak group and white oak group are susceptible to the disease, though species in the red oak group may die in as little as three weeks while white oak species can suffer through oak wilt for years before dying.

In Oakland County, oak wilt has been confirmed at 22 sites, reported at 11 additional unconfirmed sites and treated at one site, according to the Michigan DNR’s oak wilt viewer map as of March 23, 2020. The confirmed report of oak wilt nearest to Novi is in Farmington Hills near the corner of 11 Mile Rd & Halsted Rd, which is less than 1.5 miles from Novi’s eastern border.

For more information on oak wilt or to find a local Oak Wilt Qualified arborist, visit MichiganOakWilt.org.

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