Property owners, the Emerald Ash Borer (EAB) officially reached Denver in 2025, and the insect has killed hundreds of millions of Ash east of the Mississippi River. Colorado will be no different since this is a 100 percent mortality insect for untreated trees. Untreated trees in Arvada are starting to show decline. Ross Tree recommends that homeowners treat their trees between May 15 and June 15, when adult beetles emerge from trees in search of their next host. The treatment window is narrow, and missing it does not just delay action; it significantly increases the likelihood that a healthy tree will become a costly removal down the road for those who procrastinate. For more information about the EAB, click here to go to the Colorado State Extension Service website.
What Are Ash Trees Worth?
Homeowners in Denver with Ash trees need to ask themselves whether they value them. These trees have both aesthetic and monetary value. Denverites must love them, since over 300,000 have been planted in Denver proper over the last 100 years. Mature Ash are large, stately trees that grow to about 60 feet tall and have a distinctive diamond-shaped grey bark. Typically, attractive landscapes are worth about 10 percent of the home, so homeowners with mature Ash trees are really dealing with an asset preservation issue.
Ash Tree Identification
Before even getting into treatment decisions, there is a more basic question many homeowners need to answer: do they actually have an Ash tree in their yard? Ash trees are identifiable by having opposite branching, meaning limbs grow directly across from each other rather than alternating. Their leaves are compound, typically with 5 to 9 leaflets along a central stem, and mature trees develop a distinct diamond-pattern bark. Once Homeowners correctly identify their trees as Ash, they need to look into their treatment options.
What Are Systemic Injections?
Ross Tree is Denver’s leading innovator in tree insect control. We were the first tree company to offer systemic insecticide treatments for tree borers, beetles, aphids, and scales in the late 1990s. Ross Tree’s motto, “Integrity in Action,” means we are committed to minimizing the environmental impact when treating tree insects. We promise only to use what is necessary and nothing more. Trunk injections ensure that the product reaches only the tree, not the surrounding environment. We use injections to treat mature Ash trees for EAB. For younger trees, we use bark sprays.
The timing of treatment is dictated by biology, not convenience. Adult beetles emerge in mid-May, lay eggs, and the larvae begin feeding under the bark, which ultimately kills Ash trees. Systemic trunk injections work by moving insecticide through the tree’s vascular system, protecting it from the inside out as insects feed. Systemic products work when the tree is actively transpiring—after leaf-out and before peak summer stress—making the May 15 to June 15 window critical. Treat too early, and the product does not distribute. Treat too late, and the damage is already underway if the EAB is present. The real decision is not whether to spend money—it is whether to protect an asset at the optimal time or pay more for ineffective treatments. It takes about 3 years for adult beetles to be noticed on untreated trees; by then, they are lost and will require removal.
Case Studies
A University Park case study makes this clear. A $1.9 million historic home with five mature ash trees carries a landscape value of around $190,000. Treatment costs about $650 per year, while removal runs $9,000 to $12,000. Over 10 years, treatment costs roughly $6,500 while protecting well over $190,000 in landscape value. That translates to roughly $30 protected for every $1 spent.
What is more interesting is how this ROI holds across different price points. Just down the street at 2080 South St. Paul, a more modest $814,200 home has a single large ash tree with a landscape value of about $81,000. Treatment for a tree of that size runs about $500–$700 every two years, or roughly $300 annually. Over 10 years, that’s about $3,000 in cost protecting $81,000 in value—again delivering roughly $27 of value protected for every $1 spent.
Treatment is not just justified for high-end properties—it makes financial sense almost everywhere mature ash trees exist, given Denver’s high home prices.
Don’t Make This Mistake
Denver homeowners have been hearing about the Emerald Ash Borer menace since 2013, when the insect was first found in Boulder. It became like “Where’s Waldo.” It took the green beetle twelve years to reach Denver. Believe it or not, several Denver-based tree companies ran radio ads in 2103 about treating, so complacency and skepticism are natural.
As years pass, a visible decline sets in on untreated trees, and more trees cross the point at which they can no longer be saved. Eventually, removal becomes unavoidable. Treatment makes the most sense for large, healthy trees that provide shade, curb appeal, and long-term value—particularly in established Denver neighborhoods where mature landscapes are the norm. Removal becomes the right decision only when a tree is already heavily compromised or structurally unsafe.
The takeaway is simple. Homeowners should identify their ash trees, confirm their condition, and schedule treatment during the May 15 to June 15 window. At its core, this is a straightforward financial decision: spend a few hundred dollars per year to protect a valuable asset, or spend thousands later to remove it and lose that value permanently. H
Ross Tree Company has served Denver’s urban forest for over 40 years with ISA-certified arborists, comprehensive insurance, and a track record of professional tree care that prioritizes trees’ long-term health. Please call (303) 871-9121 or click here to complete a request service form. Property owners, we want to earn your business.
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