How should our Colorado HOA plan for emerald ash borer in its common-area ash trees?

By OurHOA · General information · Revised October 29, 2026

A Colorado HOA board's emerald ash borer plan: count the ash, decide which to treat or remove, hire a licensed applicator, dispose of wood and replant.

Part of the HOA board handbook: vendors, projects and upkeep.

The short answer

Emerald ash borer is an invasive beetle that kills ash trees from the inside, and it has spread through much of the Front Range. The Colorado State Forest Service first found it in Boulder in 2013, reported it in more than 20 Front Range cities by October 2025, including Denver, Aurora and Golden, and now lists Colorado Springs, Firestone, Ken Caryl and Parker among its most recent detections. Roughly 15 percent of Colorado's urban trees are ash. The board's plan has four parts: - Count every ash on common area and rate its condition. - Decide, tree by tree, which ones are worth treating and which come out on a schedule. - Hire a licensed commercial applicator for treatment and a licensed tree company for removals. - Replant with other species before the gaps open up. Doing this before trees start dying is cheaper and safer than doing it after. What the association owns, and who decides, comes from your declaration and any city rules on street trees, and those differ by community. This guide is education, not legal advice.

Count the ash first

Most boards do not know how many ash trees they have. Start there. The forest service gives three marks of an ash: branches and buds grow directly opposite each other, the leaves are compound with typically 5 to 9 leaflets, and mature trees have bark with diamond-shaped ridges. Seeds are paddle-shaped. Have a certified arborist, or a careful volunteer with the arborist checking the doubtful ones, tag each ash and record its location, trunk diameter at chest height, and how much of the canopy is thin or dead. Note what each tree would hit if it fell: a home, a walk, a playground, a parking area. If your community already has a tree inventory from our guide on planning an HOA tree maintenance program, filter it for ash and update the canopy ratings. Then check whether any of those trees are really the city's. In Denver, the adjoining property owner is responsible for street trees in the right-of-way, and a free permit from the City Forester is required to remove, plant or inject one. Fort Collins requires a permit after a city evaluation before anyone treats a right-of-way ash. Boulder lets adjacent owners treat right-of-way ash only with Boulder Forestry's permission.

Signs a tree is already infested

The beetle works under the bark for years before anyone notices. The forest service says an infestation can run 3 to 4 years before decline is visible, and a tree may die within two years after that. Adults fly from late May through September. What to look for on your walk: - Thinning from the top of the crown down, the easiest symptom to see from the ground. - D-shaped exit holes about 1/8 inch across in the bark. - Vertical bark splits over the larval tunnels, with S-shaped galleries underneath. - Shoots sprouting from the lower trunk. Other borers also attack ash in Colorado, so a hole or a thin crown does not prove EAB. If you suspect it in a part of the state without known detections, report it to the forest service or your county extension office rather than guessing.

Deciding which trees to treat

Treatment is a long commitment. You are paying for injections every few years for the life of the tree, so treat the trees that earn it. Rules of thumb from the official sources: - Treat only once EAB is verified in your community. The forest service recommends treatment only where infestations have been confirmed. Jefferson County tells owners within 1 to 15 miles of a known infestation to decide now between treating and removing, and owners farther out to monitor and water. - Treat healthy trees. The forest service says to treat trees with no more than 20 to 40 percent canopy decline. CSU Extension says emamectin benzoate can usually save a tree with up to 30 percent thinning, and that trees at 60 to 70 percent loss are beyond recovery. - Treat trees that matter. Large, well-placed shade trees near homes, along the main entry or over the pool deck usually justify the cost. A small ash in a poor spot, or one already crowding a sidewalk, is a removal candidate. CSU says there is no fixed guideline on when to start, so the board has to choose. Get two prices: treatment per tree for one cycle, and removal plus stump grinding for the same tree. Purdue University's free EAB cost calculator compares the two over 25 years and assumes untreated ash in an infested area can no longer be saved about 8 years after detection. The City of Boulder notes that treatment is inexpensive compared with removing and replacing a tree. A sample motion: "Move to treat the 14 ash trees rated good or fair in the arborist's report dated March 3 with emamectin benzoate this spring, to remove the 6 ash rated poor over the next two years starting with those near homes, and to add both costs to the operating budget."

Hiring the applicator

CSU Extension's fact sheet on EAB insecticides covers the main options: - Emamectin benzoate trunk injection. Applied only by professionals, in mid to late spring after the leaves are out, and lasts at least 2 years. The forest service puts the cycle at every 2 to 4 years. - Imidacloprid soil drench. Applied every year shortly after bud break. CSU says it controls EAB in trees under 6 inches in diameter, and that trees over 15 inches need double rates that retail products do not allow. Soil treatments cannot go down when flowering plants are blooming around the base of the tree, because the insecticide can reach bees through nectar and pollen. Under Colorado's 2023 law SB23-266, neonicotinoids such as imidacloprid became limited-use pesticides sold only through licensed dealers, which is another reason this is not a volunteer project. The forest service says to hire only professionals certified by the Colorado Department of Agriculture. Anyone who applies pesticides for hire needs a commercial applicator license under Colorado's Pesticide Applicators' Act. Ask for the license number, the product name and rate, a tree-by-tree list keyed to your tags, and proof of insurance. Put the treatment dates in the inventory so the next board knows when the next round is due.

Removing ash and handling the wood

Do not wait for the removal list to fail on its own. The City of Boulder says infested ash dry out quickly, become brittle and are more prone to fail, and that once trees show symptoms it is not safe for arborists to climb them. That means bucket trucks or cranes, and a higher bill. Removing poor trees on a two- or three-year schedule, starting with the ones over homes and walks, spreads the cost and keeps the hazard low. Our guide on removing a dead or dangerous tree on HOA common area covers the board vote and owner notice. The federal EAB quarantine ended January 14, 2021, but the wood still spreads the beetle. The forest service asks everyone not to move ash, hardwood firewood or untreated ash wood to other locations. Its disposal guidance for your contract: - Chip ash to smaller than 1 inch by 1 inch, or remove the bark, before moving it. - Use the wood only at the site where it was cut. - Schedule removals for September 1 through late April when you can. Summer removals should go to a landfill. - Do not let owners haul off rounds for their fire pits.

Replant, and a three-year timeline

The Front Range Tree Recommendation List, put together by CSU, the forest service and city foresters including Denver and Fort Collins, marks all ash species as prohibited for planting. It lists alternatives such as hackberry, Kentucky coffeetree, bur oak, thornless honeylocust, lindens and disease-resistant elms. Check each species' rating and size on the list against the planting site. The forest service also says no single tree species should make up more than 10 percent of the trees you plant. Ash is the lesson in why: a street lined with one species can lose all of it to one pest. Year 1, winter: arborist inventory of every ash. Spring: board adopts the treat and remove lists, first injections after leaf-out, first removals of the worst trees near homes. Fall: plant replacements. Year 2: walk the treated trees in summer and move any that are declining to the removal list. Continue removals between September and April and keep planting. Year 3: second round of injections if your product is on a 2-year cycle. Update the inventory and set the long-term budget line for treatment. The mistakes that cost the most: waiting until trees are 70 percent dead to start treating, treating every ash including the ones in poor spots, letting a lawn crew drench big trees with a retail product, and giving away ash firewood. Keep the inventory current and every decision gets easier.

Sources

These guides are general education for HOA boards and residents, not legal, tax, or financial advice. Rules vary by state and by your community's governing documents - check with a professional for your situation.

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