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Informed tree owners the best defence again oak wilt, city says

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Pam Wright

Sarnia officials are hoping homeowners will “get out in front” of a beetle-borne disease threatening the city’s oak trees.

The invasive fungus “oak wilt” has reached Belle Isle near Detroit and across the border in St. Clair County, Mich.

“It’s inevitable, it’s coming,” said Patti Ross, city’s parks and forestry manager. “I hoping we can mitigate it and stall its progress.”

The virus affects the vascular system of oak trees by choking off the flow of water and nutrients. Once infected through a fresh cut or “wound,” the disease usually kills a tree in 30 to 60 days.

“There’s no saving it at that point, if it’s infected,” said Ross, who estimates 2,500 municipal oaks are at risk, including 700 on boulevards and the rest in parks and public lands.

Within the oak family, red oaks are the most susceptible.

Not only do tree losses hurt the environment, Ross said, they can significantly impact a property’s esthetic and financial value, including the expense of removing dead trees.

The arrival of oak wilt in Canada will be another blow after the devastation wrought by the invasive Emerald Ash Borer, Ross said.

To prevent the spread of oak wilt, city tree owners are being asked not to prune oak trees between April 15 and July 15. That’s when sap-eating “picnic beetles” actively carry fungus spores between trees and can transfer them to those with an open wound.

Likewise, storm damage and construction injuries leave trees vulnerable.

Firewood can also harbour the fungus and so it shouldn’t be moved, Ross said.

And finally, oak wilt is spread through interlinked roots, which should be severed by ‘trenching’ when a tree becomes infected.

A March 28 public information session is planned for council chambers at City Hall, from 10:30 a.m. to 12:30 p.m.

Richard Wilson, from Ontario’s Ministry of Natural Resources and Forestry, will offer tips on identifying and deterring the disease. And Philip Kurzeja, an oak wilt specialist from Michigan, will discuss scientific aspects of the blight.

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