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Emerald Ash Borer Detected in Longmont

Posted on: June 8th, 2016

Emerald ash borer (EAB) was detected in Longmont, CO, on Monday, June 6th, at a residential location which has not been officially released. The detection falls within an existing EAB quarantine area around Boulder County, in which the City of Longmont resides in. The quarantine area was set up in an effort to prevent the human-assisted spread of this devastating insect.

It is still unclear whether the insect arrived in Longmont naturally, or unknowingly by human transportation.

EAB was first detected in Boulder in September of 2013. This is the first known case of EAB detection outside of the Boulder city limits.

Emerald Ash Borer Detected in Longmont


According to a press release from the Colorado State Forest Service, Longmont is estimated to have an ash tree population of approximately 43,000 trees. The City’s Forestry Services department manages 2,800 of those trees, located in public rights-of-way, parks and other city properties.

The City of Longmont has been preparing for EAB since its arrival in Colorado back in 2013. A dedicated treatment plan, originally slated for release in 2017, has now been pushed up – protective treatment of public trees has become the priority. Treatment of the first 300 trees will take place early this summer.

Now that EAB has been detected in Longmont, what does that mean for homeowners along the Front Range? If you have an ash tree, you need to plan ahead. Waiting to treat until after the borer is discovered on your property or an adjacent property is probably not the best strategy. Residents should take action now to evaluate and determine treatment needs for their ash trees.

Swingle has compiled some commonly asked questions regarding EAB treatment.

How big of problem is EAB?
EAB is now considered the most destructive forest pest ever seen in North America. Just in the Denver area alone, there are 1.45 million ash trees at risk.

How do I know if I have an ash tree?
We recommend a Landscape Care Consultant visit your property to verify your ash tree inventory. However, ash trees have:


  1. Compound leaves with 5 to 11 leaflets
  2. Branches and buds in pairs directly across from each other (opposite branching)
  3. Mature bark has diamond-shaped ridges

How do I know if my tree is infested with EAB?
Initial detection is not easy. It may take 4-5 years for the canopy of an infested ash to thin and decline. Since borers infest the upper branches of the tree, the “D”-shaped holes cannot be seen from the ground until the tree is severely infested.

How effective are insecticide treatments against EAB?
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. EAB 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 to better withstand attacks from insects and diseases.


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