Pests that Infest Ash Trees in Denver: What to Look for and How to Protect Your Trees

As a Colorado resident, you know that our state is known for its beautiful ash trees. Unfortunately, pests are an all too common problem for ash trees in Denver. In this blog article, we’ll identify the most common pests that infest ash trees across the Mile High City, beyond just the Emerald Ash Borer beetle, explain the damage each pest can do, and outline some preventative tree care and maintenance needed to protect your ash trees from pests!

Which Pests Commonly Prey on Ash Trees in Denver?

The Emerald Ash Borer beetle, or EAB as it’s often referred to, usually steals the spotlight in articles and conversations regarding pests that threaten ash trees across the U.S., including Denver. Unfortunately, the EAB is far from the only ash pest in town! It is important to familiarize yourself with the plethora of pests that prey on Colorado’s beautiful ash trees. They could be in your backyard or right under your nose!

There are a few common pests that tend to specifically target ash trees in the Denver area, including:

  • The Lilac Ash Borer (Podosesia syringae) – this beautiful, although dangerous pest loves feeding on Purple Autumn Ash and White Ash trees. It’s a clearwing boring moth that mimics paper wasps (similar in appearance).
  • Red Headed Ash Borer (Neoclytus acuminatus) prefers ash species. It is an elongated and slender beetles with long antennae, a red head, and yellow bands across its wings.
  • Ash Bark Beetles (Hylesinus spp.) are small, drab colored beetles about 1/8 of an inch long. Their antennae have feathery appendages at the end. 
  • Ash Leaf Curl Aphids (Prociphilus fraxinifolii) loves feasting on green ash trees. They are small yellow-green insects with brown heads and are covered in whitish, waxy threads.

Many of these pests can be tricky to identify on your own and are quite adept at hiding. This is why it’s important to have a professional arborist inspect your trees on a regular basis. (We happen to know a few on our team!)

A certified arborist will be able to identify pests and diseases early on and recommend a course of treatment. Prevention is always the best medicine when it comes to protecting your ash trees from pests!

What Damage Can These Pests Do To Denver Trees?

You’re probably wondering, how serious are these pests? Why haven’t I heard of them before?  Well, most of these pests are fairly common in Colorado and cause millions of dollars in damage to ash trees every year!

Some common problems caused by these pests include girdling, where the tree is unable to transport water and nutrients up the trunk, causing the leaves to wilt and die, and canopy dieback, where the leaves of the tree begin to die and fall off.

Each pest wreaks havoc on ash trees up and down the Front Range in its own unique way. The damage presents itself differently in each tree species. Here are a few details on the type of damage and signs your ash tree may display if it’s infested:

  • The Lilac Ash Borer are devastating to ash trees. The pest bores into the trunk of young ash trees, causing the tree to die. You’ll know if your tree is infested because there will be D-shaped holes in the bark and sawdust around the base of the tree. Repeated injuries can seriously weaken tree strength and impede sap flow. Grass and sawdust may accumulate in bark crevices underneath holes. Pupal casings may extend out of bore holes.
  • The Red Headed Ash Borer – Similar to the Lilac Ash Borer, this insects larvae feed underneath the bark and create tunnels, which may decrease sap flow and make trees structurally weaker. The Red Headed Ash Borer typically targets very stressed or dying trees, and may indicate that your tree has other issues. Adults may be very apparent on the bark of trees on warm days in early spring. You may also encounter the Banded Ash Borer, which acts in a similar fashion.
  • Ash Bark Beetles start their more significant damage when females begin laying eggs and also with larval feeding. Adults lay eggs in a line under the bark that are generally perpendicular to the branches, and larvae tunnel up and downward (parallel to the branch) from the initial line, creating a distinct pattern.
  • Ash Leaf Curl Aphids feeding on ash trees cause leaves to curl and thicken. Some distortion and twisting of adjacent twigs may also occur. 

Yikes! This sounds like a lot of threats to your trees. Don’t be intimidated, most of these pests can be kept at bay. Strong and healthy trees have the ability to fight off infestation. The best defense is a good offense, so proper tree care is essential to preventing these little critters from wreaking havoc on your property.

How Can I Prevent An Infestation?

The time to create a preventative tree care plan is now!  Here are some tips on how to keep your ash trees healthy and free from pests:

  • Properly fertilize your trees. This will ensure they have the nutrients they need to stay strong and fight off pests.
  • Water regularly. Ash trees need water to stay hydrated and healthy, especially in the arid Colorado climate, so make sure they are getting enough!
  • Prune dead or damaged branches where pests are likely to lay eggs.
  • Place mulch around the base of the tree to prevent beetles from crawling up the trunk.

Watering and fertilizing your trees and shrubs properly is a key part of preventative tree care. Be sure to water early in the morning so the sun can dry the leaves and discourage fungal growth. Different ash tree varieties require different amounts of water and different types of fertilizer, so always consult with one of our expert arborists to find out exactly what your exact trees need.

If you do suspect your trees are infested with pests, contact our team of experienced tree professionals immediately. We will be able to properly diagnose the problem and recommend a course of treatment.  Don’t wait until it’s too late to save your ash!

At Fielding Tree & Shrub Care we follow a tried and true tree care strategy:

Step 1: On-site Assessment

One of our certified arborists will perform a comprehensive on-site examination of your property. During the consultation, we identify each species of tree and shrub, looking for signs of infestation, damage, and disease. We carefully determine each tree’s condition, specific needs, and the time of year that will yield the best results for treatment.

Step 2: Implement Treatment Plan

We will coordinate the scheduling of your services based on your specific tree and shrubs’ needs, time of year, and availability. Our crew of licensed, insured arborists implement your maintenance plan to get your trees and shrubs looking their best.

Step 3: Ongoing Tree Maintenance

Ongoing tree maintenance includes continuing to protect your trees from pests and disease, annual fertilization, and complimentary spring consultations. When we visit your property in the spring, we check for any changes in health and safety and make adjustments as needed based on our findings.

Pests can cause a lot of damage to ash trees if left untreated. By being proactive and taking preventative measures, you can help keep your trees healthy and looking their best.

The time is now! Schedule your consultation and fight ash tree pests today!