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Denver’s Ash Trees Ready for Second Treatment

If you were out and about in Denver in 2016, you likely saw hundreds of ash trees wrapped in plastic that said, “Be A Smart Ash.” Denver Parks & Recreation’s Office of the City Forester treated public right-of-way ash trees adjacent to private properties throughout the city to prevent an Emerald Ash Borer (EAB) infestation. Although the treatment of ash trees by a tree care professional is 90% effective, treatment must be repeated every two to three years to remain successful. With this in mind, we will be treating these trees again.

Healthy ash trees that are 12 inches and larger in diameter at four feet off the ground were put on a list for potential treatment. From this list, a number of trees were randomly selected in each neighborhood to be treated in either 2016, 2017 or 2018.  Because trees require treatment every two to three years, we’re revisiting the 2016 trees now. Every ash tree scheduled to be treated was examined by a city arboreal inspector to determine if it was a good candidate for treatment.

EAB is a destructive pest that kills ash trees and poses safety and financial risks. However, this treatment, when done in advance, is more than 90% effective in preventing tree death.

photo courtesy of @watersa on Instagram

Risks of avoiding treatment Include:

  • Ash trees killed by EAB become very brittle and can break easily. Dead ash trees are dangerous to you and your neighbors and can be expensive to remove.
  • You are responsible for removing infested or dead EAB trees on and adjacent to your property, so treat your tree!
  • EAB has the potential to destroy Metro Denver’s 1.45 million ash trees – roughly 1/6 of Denver’s trees – significantly impacting our precious tree canopy.

Trees are critical for our overall quality of life. They produce oxygen, reduce smog, cool our neighborhoods and homes and increase our property values. Join our effort to save Denver’s ash trees by talking to your neighbors, friends and co-workers about EAB and encourage people to visit for more information. To see which ash trees are being treated and those that are candidates for future treatment, visit