The Homeowner’s Guide to Emerald Ash Borer (EAB)

Fielding Tree Emerald Ash Borer Denver

Boulder has been under quarantine since the arrival of EAB in 2013. But the Denver Post reports that just earlier this year the Emerald Ash Borer infestation spread to Lyons. Denver is not safe from the destructive path of EAB. Learn how these pests do damage and how to protect your ash trees before it is too late!

What Is the EAB and What Does the Emerald Ash Borer Do?

The Emerald Ash Borer Beetle is a non-native wood-boring insect, believed to have first made its arrival in the U.S. in Michigan as part of an international shipment of wood from China. The EAB is now arguably the most destructive pest in the United States, killing all types of North American ash species such as green, white, black and blue ash, and their cultivars (including autumn purple ash, a popular white ash varietal in Colorado).

How does the EAB do damage to ash trees? In the larval stage, EAB cuts off the flow of water and nutrients to the tree by feeding under its bark. Once a tree falls victim to infestation, there is no saving it. Infested trees gradually die over a period of approximately two to four years.

How far and how quickly does the EAB spread? They are known for being strong fliers, but EAB adults rarely fly less than half-a-mile from their emergence tree. In fact, humans moving ash firewood or ash nursery stock is thought to be responsible for the known cases of EAB moving long distances. For this reason, movement of other untreated ash wood, wood chips greater than one inch, and ash products (green lumber, pallets, etc.) should be avoided at all costs.

How to Spot EAB

Now that you know how dangerous EAB are, you need to be on the lookout in your neighborhood and on your property for these pests. Luckily, EAB adults are pretty easy to identify. They are a shiny green metallic color, with red or purple under the wings. Measuring approximately 1/2-inch long and 1/8-inch wide, EAB is often mistaken for the Six-Spotted Tiger Beetle and the Japanese Beetle. Reference photos and information on the Colorado Department of Agriculture website to quickly tell the difference. If you have indeed identified EAB, the Colorado Department of Agriculture asks that you file a report. You can also see a map where the Colorado State Forest Service has confirmed EAB infestations in Boulder and northern Denver.

EAB adults are usually active and visible in June and July when they lay eggs on the bark of ash trees, but they may be present from late May to September as well. EAB larvae are hidden and not as easy to find as EAB adults. Nestled under the tree bark, the larvae are a milky white color. EAB larvae create S-shaped tunnels that are noticeable if you strip away bark using branch-peeling techniques.

Not sure if you have actually found EAB? Don’t ignore the possibility. Talk to one of our knowledgeable arborists about the possible presence of EAB in or on your ash trees. Taking action immediately will help save your trees and others in your community.

How Will EAB Affect Me?

Boulder County alone has spent more than $200,000 on the EAB crisis. This means higher taxes! Local officials are busy proactively treating healthy trees, removing dying ones and educating the public. According to the Colorado State University Extension, an estimated 15 percent or more of Colorado’s urban and community trees are ash, and many of these trees are located on private property.

It’s important to understand EAB infestation is almost always fatal to infested ash trees. You need to take stock of your trees and make a plan to treat them before the EAB arrives, or they will be dead within approximately four years. EAB is the most destructive forest pest in recorded U.S. history! There are a number of factors you’re probably considering. Do I have any ash trees? What do I need to do as a property owner in Denver? Should I treat my ash tree? Is it worth trying to preserve?

These are all valid questions. The good news is, protecting your trees is completely within your control. The best step you can take is contacting one of our certified arborists at Fielding Tree & Shrub Care for a complimentary consultation. They can answer all your questions, explain how EAB might personally affect your property, and go over all your treatment and preventative options.

What Can I Do Now to Protect My Ash Trees From the EAB?

At Fielding Tree & Shrub Care, we’ve developed a reliable plan of action for protecting trees from EAB. For starters, healthy trees that are well-watered and fed can defend themselves better from all types of insect infestation. We recommend feeding your ash trees to keep them healthy and give them a better chance of survival.

Insecticide treatment options are available to effectively treat landscape ash trees threatened by EAB. Field tested and evaluated by university and government scientists, these methods are safe and proven to work. Here are two types of treatment and delivery that we recommend for success:

Soil-root injection to prevent EAB infestation: this is a two-year protection program that protects against EAB and Aphids only. The industry-standard cost is $10 per inch of DBH (diameter of the tree at waist height).

Direct tree trunk injection to protect against EAB infestation: This is a three-year protection that protects against EAB and Aphids. The industry-standard cost is $15 per inch of DBH. As mentioned earlier, a tree’s DBH is the diameter of the tree at waist height.

For best results, the right time of year to apply treatment for EAB protection is in April and May. The timing has to do with the life cycle of EAB. There is a small window of opportunity to control the adults before any new eggs or larvae are produced. The onset of adult beetle emergence begins from early June and peaks two to three weeks later, lasting through July. Timing is everything!

Is treating and saving my tree from EAB infestation worth the investment? A cost-benefit analysis of EAB protection should take into account several factors: tree size, location, and health all matter as you try to put a value on your tree. Then, consider the cost of the insecticide and application vs. the potential costs of removing the trees.

Of course, it’s impossible to predict the exact likelihood of success when using insecticide treatment, and there is no guarantee that your tree will definitely remain unharmed. However, an EAB study jointly conducted by university professors entitled “Insecticide Options for Protecting Ash Trees from Emerald Ash Borer” compared costs of removing urban ash trees versus treating the same trees with an insecticide that provides two years of EAB control. The results consistently found that treatment costs are much lower than removal costs!

Beware! EAB Warning Signs

  • EAB Adult Beetles and Larvae present
  • Broken branches towards the trunk of the tree
  • A dying canopy of leaves
  • D-shaped exit holes in ash tree bark
  • Bark splintering and S-Shaped Tunnels
  • Increased woodpecker interest or damage
  • Epicormic Shoots

Keep in mind that an infected tree may have only a few or any combination of these warning signs. Ash trees with minimal EAB larvae may even show no external symptoms of infestation!

Scientists have learned that most female EAB lay their eggs on nearby trees in a range of about 100 yards of the tree from where they originated. However, some female beetles, are beginning to move much further, anywhere from half a miles to two or three miles. It is reasonable to assume that if your property is within 10-15 miles of a known EAB infestation, your ash trees are probably at risk.

What’s Being Done In Colorado to Address the Spread of EAB?

Don’t worry, it’s not up to you to save the ash trees alone. Since 2013, the Colorado Emerald Ash Borer Response Team has been hard at work with partner organizations and communities to help manage the spread and impact of the EAB. This team currently collaborates with local governments to track and map the extent of infestation.

Want to learn more or possibly get involved with EAB awareness? The team hosts EAB identification workshops for industry professionals and volunteers and leads EAB education and outreach efforts to inform the media and public.

Colorado officials recognize the serious havoc EAB will bring upon our communities. That’s why policy-makers have put in motion a $1,000 per violation civil penalty on the transportation of quarantined items such as logs and green lumber, nursery stock, wood chips and mulch outside of the designated area. More details and including additional information regarding restrictions may be found at

Take Action and Protect Your Ash Trees

Ash trees are towering, beautiful trees that are a treasure to our community spaces and home landscaping. They are certainly worth the vigilance and care it takes to protect them from the rapidly encroaching Emerald Ash Borer.

The EAB beetle is relentless and coming for ash trees in Denver. Be prepared and customize a preventative treatment plan for your trees now. The first step is to schedule your complimentary on-site inspection. With help from Fielding Tree & Shrub Care, your ash trees will live long and prosper!