What Risk Does the EAB Beetle Pose to Denver Trees?

Spring has sprung and that means the Emerald Ash Borer, which has been hiding out all winter, will soon re-emerge. Denver trees are at great risk as the EAB prepares to spread once more. As a homeowner, it’s time to spring into action to treat and protect your trees before the Emerald Ash Borer strikes. 


Emerald Ash Borer (EAB) Update

In the spring of 2020, the Emerald Ash Borer breached previous containment efforts by local agencies and advanced into the Arvada and Fort Collins areas near Denver. Experts anticipate the further spread of the EAB  into neighboring counties this year as well. 


The Emerald Ash Borer has 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. 


The proactive management solutions are simple: treat or cut down ash trees to stop the spread of the invasive EAB. 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 1 in 6 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 Ash.org. 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 options and ways local residents can help stop the spread of these ash killers. 


How Does the Emerald Ash Borer Spread?


You know the EAB are knocking at Denver’s door, but how exactly do they spread? The pests have been hiding out all winter and will soon re-emerge. EAB larvae survive the winter months by hunkering down in a small chamber in the outer bark or in the outer inch of wood. First adult beetles begin to emerge 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. 


The Emerald Ash Borer can have a one- or two-year life cycle, recent research shows, and adult beetles are capable of flying ½ mile or more from the tree where they emerge. This natural ability to travel increases the radius at risk for EAB spread. With favorable winds, the EAB could even fly several miles at a time. The Colorado Department of Agriculture’s primary concern is that EAB populations have the potential to expand exponentially.


This is in part because experience with EAB in nearby cities shows that there is often a 3-4 year gap between when trees become infested and when they are actually diagnosed and removed. The delay in diagnosis and removal gives EAB the time and opportunity that they need to spread. The Colorado State University Extension 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 the South Platte Drainage of Colorado. 


It is important 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. To address these issues, shipments of ash nursery trees and ash logs with bark are now regulated, and transporting firewood outside of the quarantined areas is illegal. 


Taking Responsibility For Saving Your Ash Trees

The risk for Denver is higher than ever and the responsibility of protecting ash trees on private property falls squarely on the homeowner. Treatment is the best approach for protecting your Ash trees from the destructive EAB, but timing is everything. There is a perfect window of time left in spring and early June to maximize the potential of chemical treatments and effectively protect your Ash trees. 


Here is what you can do now:


Recognize Your EAB Warning Signs 

One of the best things you can do to protect your trees is to learn the EAB warning signs. If you spot them on trees in your neighborhood or community, you can potentially save your trees before it is too late. Stay vigilant! Here are the 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!


Start Preventative Treatment 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

  • systemic insecticides that are applied as soil injections or drenches
  • systemic insecticides applied as trunk injections
  • systemic insecticides applied as lower trunk sprays
  • protective cover sprays that are applied to the trunk, main branches, and foliage. 


Spring Into Action

  • Spring is the ideal time of year to apply insecticide treatment for EAB 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. 


Strong And Healthy Trees Fight Infection

In the same way that healthy bodies can fight off infection, 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. At Fielding Tree & Shrub Care, we’ve developed a reliable plan of action that includes proper watering and fertilization for protecting trees from EAB. 


EAB Fast Facts

  • The Emerald Ash Borer Beetle is a non-native wood-boring insect and has no natural predators in the U.S.
  • The EAB is now arguably the most destructive pest in the United States, killing all types of North American ash 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. Once a tree falls victim to infestation, there is no saving it.
  •  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.


Team Up With Expert Arborists Today


The Emerald Ash Borer is posing a  greater risk to Denver ash trees than ever before. Untreated Ash trees will be devastated and dead within four years. Protecting your trees is completely within your control. Contact one of our certified arborists at Fielding Tree & Shrub Care today for a complimentary consultation. They can explain how EAB might personally affect your property, and go over all your customizable treatment and preventative care options.


Act now to save your trees and schedule your complimentary on-site inspection with Fielding Tree & Shrub Care today!