MINNEAPOLIS— This winter’s record warmth could continue to cause problems for oak trees in the spring and summer.
Oak blight, which has been in Minnesota for 70 years, continues to spread. Arborists like James Ostlie say the risk is even greater this year.
“It’s kind of worked its way up from the southeastern corner of the state. It’s now quite prevalent in the metro area,” Ostlie said, adding that the northern metro is being particularly hard hit.
Most damage is caused underground: by a fungus that attacks the roots of the tree and cuts off the water supply.
“The back-to-back summer droughts have made them stressed and they haven’t really gotten proper winter rest this year. I expect them to be stressed overall,” Ostlie said.
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The warm winter also killed fewer insects, which can also help spread the disease.
Just this week, the U of M Extension Office raised the risk level for oak wilt to high.
“Don’t prune your trees until the fall would be my easiest recommendation for you. We’re just creating a lot of artificial wounds, which increases the chances of your tree getting sick. If you see any kind of spontaneous brown leaves popping up, especially a whole branch that you’ve never noticed before, I would have it checked out,” Ostlie said.
Our oaks are normally considered a sturdy tree, but are becoming more vulnerable to a growing number of pests.
“They’re great for our landscape. They’ve been around for a long time. Some can live up to 150 years, even in an urban environment. That’s a really long time. So they’re fantastic, useful trees that I think we need to protect Ostlie said.
He said wilt can spread much more quickly in red oaks – and when the trees are close together.
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