Indications, Effects and Treatment for Emerald Ash Borer (EAB) in Colorado

Sadly, Denver is not safe from the destructive path of the Emerald Ash Borer (EAB) beetle. As a homeowner, it’s time to spring into action to treat and protect your ash trees before this pest strikes. It’s important to know the warning signs, the potential damage they can cause, and the steps you can take for treatment for emerald ash borer.

EAB Fast Facts

As the temperatures in Denver continue to rise and drought-like conditions persist, EAB is spreading at an alarming rate. EAB larvae bore into the tree where they happily feed on the inner bark, likely destroying the tree within a few short years.

Here’s what you need to know about EAB:

  • Adult EAB are mostly green jewel beetles, although sometimes they appear reddish due to their metallic hue and red bodies.
  • The EAB is a non-native, invasive, wood-boring insect and has no natural predators in the United States.
  • EAB is now arguably the most destructive pest in the U.S., killing all types of North American ash tree species, including autumn purple ash, a popular white ash varietal in Colorado.
  • In the larval stage, EAB cuts off the flow of water and nutrients to the tree by feeding under its bark. Time is of the essence when it comes to an infected tree. 
  • If the infestation is already present, the tree needs to be treated immediately in order to save it. The infected areas cannot be saved, but any live material of the tree can be treated to prevent further infection.  
  • EAB often goes undetected making preventative treatment the best measure for protecting ash trees. 
  • Humans moving ash firewood or ash nursery stock are thought to be responsible for the known cases of EAB moving long distances. For this reason, the 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.

If you would like to learn more about general ash tree care, we’ve put together a complete ash tree guide that you can read here

EAB Origins and Indications

EAB damage trees by tunneling under the bark and eating the phloem, which is the layer of tissue that transports nutrients from the leaves to the rest of the tree. Consequently, this feeding disrupts the tree’s ability to move water and nutrients up and down, causing the tree to starve and eventually die.

How EAB Spread

Infestation is not only a concern for the Department of Forestry or local government officials; rather, it is a problem that affects the whole Denver community. Basically, these beetles spread by flying from tree to tree and by hitching a ride on infested firewood, nursery stock, or other objects that come into contact with the trees.

Generally, we know EAB adults can fly at least 1/2 mile from the ash tree where they emerge, and they have been found as far away as 12 miles from the nearest infested ash tree. This natural ability to travel increases the at-risk radius for EAB spread. With favorable winds, the EAB could even fly several miles at a time. 

Their life cycle also contributes to the rapid spread of the infestation. Females lay about 60 to 100 eggs during her lifespan. Furthermore, she lays her eggs in the cracks and crevices of ash bark. In 7-10 days the larvae hatch and then tunnel into the tree to feed on the inner bark. This feeding disrupts the tree’s ability to transport water and nutrients, eventually killing the tree.

Additionally, these pests hide out all winter and re-emerge, alive and well, in the spring. Larvae survive the winter months by hunkering down in a small chamber in the outer bark or in the outer inch of wood. 

Come spring, adult beetles begin to emerge first in mid to late May. By late June they are in peak emergence, with female beetles laying eggs about 2 weeks after emergence. After another 1-2 weeks, the eggs hatch and the larvae begin their destruction and havoc on the tree. The feeding lasts roughly from July all the way through early October. 

State of Concern

The Colorado Department of Agriculture’s primary concern is that EAB populations have the potential to expand exponentially. This is due to the reasons outlined above, but also because of the EAB’s track record in Colorado. Specifically, Denver’s experience with EAB in nearby cities shows that there is often a 3-to-4-year gap between when trees become infested and when they are actually diagnosed and removed. Delay in diagnosis and removal gives EAB the time and opportunity that they need to spread. 

The Colorado State University Extension also predicts that this natural spread will cause the present outbreak of EAB to expand in the next few years to eventually encompass all the areas within reach of the South Platte River. 

Again, it’s crucial to note that human activity is also a key cause of spreading EAB. Many infestations begin when people move infested ash trees from nurseries, logs, or firewood to other areas that did not have infestations. Given these points, shipments of ash nursery trees and ash logs with bark are now regulated, and transporting firewood outside of the quarantined areas is illegal.

Warning Signs of EAB Infestation

Adult Beetles and Larvae are Present

Of course, the most obvious warning sign is the actual presence of adult EAB beetles and/or larvae. Adult beetles are metallic green in color and approximately half-an-inch in length. Typically, they have a flattened back with dark gray or purple segments under their wing covers on their abdomen.

Larvae are a creamy white color, legless, and most often found under the bark of an ash tree. Their bodies are typically divided into flattened, bell-like segments.

Dying Canopy of Leaves

One of the most obvious signs of infestation is the thinning of branches and leaves on a seemingly otherwise healthy ash tree. Twigs and branches begin to thin out as the tree infestation continues. Unfortunately, a dying canopy often occurs after years of untreated EAB devastation. 

D-shaped Exit Holes in Ash Tree Bark

When the larvae hatch into adult beetles, they exit the bark of the ash tree by burrowing out. This creates D-shaped holes; they’re not perfectly round because the adult beetle has a flattened back.

Broken Branches Towards the Trunk of the Tree

Healthy branches typically break in the middle of the branch, not close to the tree trunk. If your ash tree recently experienced a broken branch, check to see where the break occurred. If the break was snug to the trunk, it is most likely not an isolated issue.

Bark Splintering and S-Shaped Tunnels

Ash trees suffering from infestation often lose their bark as a result of damaged tissue. Bark splitting or bark peeling on ash trees may be reason enough to look for the telltale S-shaped galleries (tunnels) caused by EAB larvae. If you suspect EAB but your ash’s trunk is intact, you will need to create an exposed section of bark to search for the tunnels. 

Increased Woodpecker Interest or Damage

A variety of woodpecker species have a healthy appetite for EAB. Sadly, their appetite is not strong enough to keep the EAB in check. Even if that were the case, the woodpecker would destroy your tree in the process to get their fill of the beetles. If you notice an unusual increase in interest or damage from woodpeckers, it’s often an ominous sign of EAB infestation.

Epicormic Shoots

You may have never heard the term “epicormic shoots,” but chances are you know what they are. Epicormic shoots are the short, tree-like shoots that grow out from the base of your trees. Most homeowners simply disregard these shoots as wild growth from a tree, and often that is the correct assumption.

However, ash trees infested with EAB larvae will send out epicormic shoots because the tree knows its life is at risk. This is the tree’s survival mode kicking in to try to outgrow its new threat. Additionally, Ash trees with EAB damage will often grow larger-than-normal leaves on their epicormic shoots.

Treatment for Emerald Ash Borer

There are several preventative steps you can take in the treatment for emerald ash borer. Proper watering, mulching, trimming and fertilizing can all make a big difference before the EAB emerge in late spring and early summer. With proper care and preventative treatments, your Ash trees will stand a good chance of evading an outbreak of EAB.

Start Preventative Treatment for Emerald Ash Borer Immediately

Chemical insecticides are available to effectively treat landscape ash trees threatened by EAB. It is best to begin using insecticides while ash trees are still relatively healthy. If insecticide treatment begins after the first signs of infestation, such as canopy thinning, it can stop additional damage, but it will not reverse any damage that has already been done. 

EAB Insecticides work systemically and have to be transported within the tree. This means that a tree must be healthy enough to transport a systemic insecticide up the trunk and into the branches and canopy. Trees within an established EAB infestation have developed galleries under the bark that prevent the transport of the insecticide throughout the tree, and therefore it will not be effective in these trees.

Insecticides that can effectively control EAB fall into four categories

  1. Systemic insecticides applied as a trunk injection. Direct tree trunk injections are a two-year protection program that protect against EAB and a wide variety of other insects.  In certain cases, this can actually be more cost effective than alternative yearly applications.
  2. Systemic insecticides that are applied as soil injections or drenches. Soil-root injections and soil drenches are an annual protection program that only protect against EAB and aphids. These treatments must be repeated every year to maintain protection, and are the least effective method.
  3. Systemic insecticides applied as lower trunk sprays. Basal bark sprays are an annual protection program that protects against EAB.
  4. Protective cover sprays that are applied to the trunk, main branches, and foliage. Full coverage sprays are an annual protection program that protect against EAB and aphids, but similar to basal sprays, and are not as effective as systemic applications.

Spring is the ideal time of year to apply insecticide treatment for emerald ash borer protection.

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 in late June and peaks two to three weeks later, lasting through July. Timing is everything!

Proper Watering

Trees need 2 gallons of water per 1 inch of tree diameter (measured at knee height) per week. to stay healthy. During times of drought, they may need up to two inches per week, especially if there is absolutely no rain. You can help trees get the water they need by using a soaker hose or drip irrigation system, and by watering deeply and infrequently rather than shallowly and daily.

Drought and Tree Stress

Drought has several negative impacts on Denver’s trees beyond not getting enough water. Thirsty trees are under duress, and this stress leaves them more susceptible pets and disease. Furthermore, drought dries out the tree’s soil, making them more susceptible to erosion. Trees with eroded soil suffer with less soil around their foundation and experience degradation of water quality. 

With their defenses down and their immune systems weak, Denver trees have extreme difficulty fending off an EAB infestation. Healthy trees have the ability to fight back, so the best thing you can do right now is to take steps to help your trees regain their strength.

Effective Mulching

Mulch is a layer of material (usually organic) that you spread around the base of a tree. It helps to conserve moisture after rainfall and watering. It also protects the tree’s roots from extreme temperature changes, compaction, and weed growth.

You should spread a layer of mulch that’s about two to four inches deep, making sure not to pile it up against the trunk of the tree. We recommend using wood chips, shredded bark, or pine needles.

Winter Tree Trimming

EAB prevention tips include professional tree trimming and pruning. It’s important to have your trees trimmed on a regular basis. It’s important to have your trees trimmed on a regular basis. Not only will regular tree trimming improve the overall health of your tree, but it will help fend off diseases and pests, like the EAB.

There are a few other reasons why trimming and pruning can help fend off EAB infestation:

  • Regular tree trimming will promote strong, healthy growth. 
  • Pruning removes dead and weak wood that EAB prey on.
  • Well-maintained trees enhance curb appeal and help with property value.
  • Properly pruned trees reduce risk of falling branches and storm damage.

If you want to take charge and trim your own trees, our team of certified arborists have put together a DIY tree trimming guide for that purpose. 

Consistent Fertilizing

Fertilizing your trees is like giving them vitamins. It helps them stay strong and healthy, which in turn helps them to fight off pests and diseases.

When you fertilize your trees, you should use a slow-release fertilizer so that the nutrients are released over time. This is especially important in the spring when trees are starting to grow again after a long winter.

There is no one-size-fits-all fertilizer, but our expert arborists can create a custom fertilization plan based on what your Ash trees need. We can also provide recommendations for the appropriate method of fertilizer application and how often it is needed.

Investment Considerations for the Treatment of Emerald Ash Borer

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 versus the potential costs of removing the trees.

Of course, it’s impossible to predict the exact likelihood of success when using insecticide treatment for emerald ash borer, 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.

The Current State of EAB in Colorado

Emerald Ash Borers have posed a challenge to the front range area since its first appearance in Boulder, CO in 2013. The shiny green pests attack only true ash species, and it is estimated that the Denver Metro area has 1.45 million ash trees! In addition, about 15% of Colorado’s urban forests are made up of ash tree varieties. 

They have since spread to the cities of Arvada, Westminster, Longmont, and Broomfield. To slow the spread, the Colorado Department of Agriculture and Boulder County enacted a quarantine of raw Ash material. Although the quarantine stopped the human spread of EAB, it could not fully contain the pests. They are able to fly upwards of half a mile and travel to new territory on their own, even without human aid. The quarantine was lifted in December of 2019, and ash wood is now allowed to be moved freely throughout the state of Colorado.

Major benefits of the quarantine were that it gave surrounding areas time to prepare for the impending infestation. The cities of Broomfield and Westminster took proactive steps such as reducing the ash tree population on public lands, treating high-value ash trees with chemical controls, and developing biocontrols to combat the EAB. Arvada developed a thorough Emerald Ash Borer Management Plan that was released just weeks prior to the confirmed presence of the pest.

In the spring of 2020, the emerald ash borer breached previous containment efforts by local agencies, and has advanced as far as Fort Collins.

Denver’s City Forestry team is currently implementing an Ash Tree Removal and Replacement Program in conjunction with the Denver Parks and Recreation Department. Recognizing that one in six Denver trees are ash trees, the City Forestry Team is offering Denver residents the opportunity to get rid of a right-of-way ash tree that is in poor condition and receive a free new tree. 

Any homeowner knows that tree removal and stump grinding is expensive, but this public works service is at no cost to the homeowner and has been recognized as an effective EAB management strategy. 

To learn more about the most current updates on Denver’s strategic EAB management plans, check out Be A Smart The site offers helpful information such as an interactive map that allows you to search your address and will illuminate ash trees on and around your property. There is also up-to-date information on treatment for emerald ash borer and ways local residents can help stop the spread of these ash killers.