MINNEAPOLIS (WCCO) — Experts say don’t prune your ash tree yet or it could make it more vulnerable to the emerald ash borer.

The active ash borer season is extended until Oct. 1 this year, according to the U.S. government. The beetle is typically inactive from Labor Day through May 1, but this summer it was unusually warmer.

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The beetle, which has attacked and killed millions of trees in 15 states, has been very destructive.

Minneapolis said that 20 percent of the tree canopy is made up of ash trees in the city.

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The Minnesota Department of Agriculture said that ash tree pruning should only be done during dormant times so the borers won’t spread from tree to tree. They’ve also issued a state quarantine on firewood, ash trees, and ash tree products to stop the spread.

More Information on emerald ash borer and ash trees:

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MDA: Pest Management
MN Dept. Of Ag: Save Our Ash
Mpls. Park Board