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Ash Tree Protection

Ash Borer Treatment – Why protect your ash trees?

Emerald ash borer was first detected in Boulder in September of 2013. It has since been detected in Longmont, Gunbarrel and most recently in Lafayette.

The Be a Smart Ash Campaign was started back in May of 2016 by the City Forester and Denver Parks and Recreation. It’s sole mission is to actively educate the public about emerald ash borer. We value their insight and initiative, and continually consult them for the latest news regarding their efforts. You can rest assured that Swingle Lawn and Tree will always have the most up to date information available.

EAB in the news


  • Consult an expert to evaluate your trees and make recommendations
  • Do not plant new ash trees – we suggest the following trees to plant in place of an ash tree
  • Do not move firewood made from ash trees out of the area
  • Prune dead branches – they weaken the tree, making unlikely to survive attacks
  • Additional recommendations may include fertilization and treatment for lilac/ash borer

Protecting pollinators while treating

Depending on the size of your ash tree, Swingle may recommend a soil or trunk injection to treat against emerald ash borer (EAB). However, if the base of your tree has flowering plants near its root system, which are often visited by bees and other pollinators, Swingle will NOT perform a soil injection. The product for a soil injection is directly injected into the ground near the roots of the tree, and may compromise the toxicity of flowering, pollinator-friendly plants. A trunk injection will then be utilized as we continue our environmental efforts to protect the pollinators of Colorado.

Emerald Ash Borer Videos

Understanding Emerald Ash Borer

Emerald ash borer is considered the most destructive forest pest ever in North America. It is responsible for killing more than 50 million ash trees in 29 states. Across the front range of Colorado, 1 out of 6 trees are at risk.

Identifying if you have an ash tree

Plants form foliage buds in two ways – opposite and alternate. That is, the buds (leaves) are either directly across from each other (opposite) or found on different positions along the branch (alternate). The foliage buds in ash trees are found on opposite sides of the twig.

The leaves of ash trees are also distinct in that they are formed in 5 – 11 leaflets. The only other tree that has both alternate buds and leaves formed in leaflets is the boxelder. Boxelder always has either 3 or 5 leaflets.

Effectiveness of treatment

Under experimental conditions, most results indicate a 90 percent or higher success rate.  In practical applications, success rates for insecticide treatments are at least 80 percent effective.  Why the difference?   Trees treated early, and in good vigor, have the highest success rate.

The insecticides used to combat EAB are nearly all systemic.  That means the insecticide is placed in the soil or injected directly into the trunk of the tree.  The insecticide is taken up into the tree via the vascular system.  Emerald ash borer and other ash borers feed in that vascular system as well.  When the insects have compromised the vascular system, the insecticide is not able to disperse evenly throughout the tree.

In addition to treating for EAB, trees should also be pruned while following other good horticultural practices emphasizing tree health.

How long to treat

Emerald ash borer infestations follow a definite curve.  For the first 3 years, EAB goes undetected while it’s infesting trees.  During the next 2 to 3 years, borer populations build.  During this “cusp” period, preventive treatments are recommended.  For the next 10 years, the borer goes through an exponential growth phase.

Treatments for EAB are essential.  The result: most of the treated trees live, while nearly all the untreated trees die.  With few trees left for EAB to infest, the populations of EAB will decline rapidly.  Researchers in the mid-west are now looking at this post mortality phase.  It looks as if treatments may be scaled back after this period.

What to expect from treatment

If the tree is not treated it will die, that is a known fact.  Some have asked, “If I treat my tree, will it look the same as it does now?” Maybe…and maybe not.

While the success rate for insecticide treatment is very high, when emerald ash borer becomes prolific, they will challenge the tree – or begin feeding on the tree before the insecticide controls them.   Thus ash trees, even when treated, will accumulate more dead branches than normal and have a more sparse appearance to the tree canopy.   When the EAB mortality curve subsides, the ash should return to its normal vigor.

So what does that mean for you? Sooner than later, if you have an ash tree, you need to plan ahead especially if you are in the Denver metro area. Waiting to treat until AFTER EAB in Denver is discovered on your property or an adjacent property is NOT a good strategy.

Suitable trees to replace an ash tree

We recommend the following trees should you choose to replace an ash tree on your property: big tooth maple, state street maple, pink sensation boxelder, caddo sugar maple, western catalpa, honeylocust, Kentucky coffee tree, Texas red oak, bur oak, chinkapin oak, English oak, shumard oak, London planetree, chokecherry, linden, hackberry.

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Signs of Infestation

Initial detection of emerald ash borer in ash trees is difficult. While we recommend treating your trees before the signs are visible, here are a few things to look out for on your property.

Signs of infestation include:

Canopy dieback: As EAB infestation increases, the trees canopy will begin to thin out. Dieback occurs when larva feeding disrupts nutrients and water flow to the top of the tree, resulting in leaf loss.

Epicormic Sprouting: Trees will try to grow new branches and leaves when they are stressed or sick. In later stages of infestation, ash trees will form sprouts from the trunk just below where the larva are feeding.

Bark splits: Vertical splits in the bark are caused by callus formation.  Callus is a natural response to wounding and develops around larvae galleries, exposing “S”- shaped paths underneath the bark.

Woodpecker feedingWoodpeckers eat emerald ash borer larvae. Damage will first occur at the top of the tree where EAB begins to attack.

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Unsure if your tree is a city tree?

If you’re unsure if an ash tree on your property is the cites responsibility or the homeowners, “read more” to find helpful information from the City of Denver.

CLICK HERE for the City of Denver tree inventory site

  • Enter your address into the search box at the top left of the page
  • Blue triangles indicate a city tree that belongs to the Forestry Department
  • Green Circles indicate a parkway tree that belongs to the Parks and Recreation Department
  • Clicking on the triangles or circles will open a window that shows the species, address, ID # and size range of the tree
  • If the blue tree is an ash, it will include a line for “treatment cycle” (ash trees only)

Key of Terms:

  • N/A means the tree has not been selected for treatment by the city
  • Cycle1 means the tree was selected for treatment in 2016
  • Cycle2 means the tree was selected for treatment in 2017
  • Cycle3 means the tree was selected for treatment in 2018
  • Note: Ash trees that are a green circle will not show if they were selected for treatment
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Free ash tree property evaluation

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Many of our technicians are certified by the International Society of Arboriculture
and/or State Department of Agriculture for their areas of expertise.

Tree Care Industry Association       Colorado Department of Agriculture

International Society of Arboriculture       Occupational Safety and Health Administration


Tree Service

Are your technicians certified?

Yes. Swingle is one of the few landscape organizations in Colorado to be certified OSHA compliant. In 1970, the Occupational Safety and Health Administration (OSHA) was created. The goal was to help create a safer work environment by working with businesses to establish standards that are workplace-specific. The rules and regulations developed ensure workers are in the safest environment possible as set forth by OSHA. Swingle spends more time on training hours and invests more money in industry related training than any other Colorado tree company.


Additionally, many of our lawn and tree care experts have gone through rigorous training and are certified through TCIA (Tree Care Industry Association) and ISA (International Society of Arboriculture).

Tree Service

What steps will be taken to ensure my property is not damaged?

When utilizing bucket trucks, cranes and other large vehicles on your property, Swingle will lay down protective coverings in order to make sure heavy tires will not damage your property. Potted plants, lights, patio furniture, and decorative yard art should be moved from around trees before crews arrive to perform the work. Additionally, we remove your tree in stages, starting at the very top, to lessen the chances of the tree falling onto your home or homes around you. We work directly with the power company to make sure that electrical and telecommunication lines are safely moved out of harm’s way.

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