Minnesota's warm winter could mean problems for oak trees across the state

MINNEAPOLIS — The record warmth this winter could continue to cause problems through the spring and summer for oak trees.

Oak wilt, which has been in Minnesota for 70 years now, continues to spread. Arborists like James Ostlie say the risk is even greater this year. 

"It's kinda been working its way up from the southeast corner of the state. It's pretty prevalent in the metro area now," Ostlie said, adding the north metro is getting hit especially hard.

Most of the damage is done underground — by a fungus that attacks the tree's roots, cutting off its water supply. 

"The consecutive summer droughts put them on edge and they didn't really get their proper winter's rest this year. I expect they're going to be stressed overall," said Ostlie.

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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 increased 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 that you could just increase the odds of your tree getting sick. If you see any sort of spontaneous brown leaves popping up, especially an entire branch that you've never noticed before, I'd get it checked out," said Ostlie.

Normally considered a hearty tree, our oaks are becoming more fragile with a growing number of pests.

"They're great for our landscapes. They've been around for a long time. Some of them can live up to 150 years, even in an urban site. That's really, really long. So they're fantastic, beneficial trees that I think we should protect," said Ostlie.

He said wilt can spread much quicker in red oaks -- and when the trees are grouped closely together.

If you're curious about getting your trees diagnosed, click here.