Dutch Elm Disease Back in Colorado

Great Western Tree Care – An Arborist’s Guide for Homeowners

For many Colorado neighborhoods, mature elm trees are more than just landscaping—they are history. American elm and Siberian elm were widely planted in the early and mid-1900s for their fast growth, beautiful arching canopies, and deep shade. But today, elm populations face a serious threat: Dutch Elm Disease, one of the most destructive tree diseases in North America.

As certified arborists, we work with Colorado homeowners every year to diagnose, treat, and prevent Dutch Elm Disease (DED). Understanding how the disease works and what early signs to watch for can make the difference between saving a tree and losing it.

What Is Dutch Elm Disease?

Dutch Elm Disease is a fungal disease caused by Ophiostoma species fungi. Despite the name, the disease is not Dutch in origin—it was first described by Dutch scientists in the 1920s, which is how it got its name.

The fungus spreads through:

• Elm bark beetles, which carry spores from infected trees to healthy ones
• Root grafts, where adjacent elm trees’ roots grow together underground
• Movement of infected firewood or pruning debris

Once inside the tree, the fungus spreads through the vascular system, blocking water transport and causing the tree to wilt and eventually die.

Why Dutch Elm Disease Matters in Colorado

Colorado still has many mature elms in older neighborhoods, parks, and along streets. Some of these trees are 60–100 years old, providing massive shade and property value. Losing a mature elm can dramatically change a landscape—and replacing one takes decades.

Colorado’s dry climate helps reduce some diseases, but Dutch Elm Disease persists here because:

• Elm bark beetles are active across the Front Range
• Neighborhoods have many elms growing close together
• Root grafts allow rapid spread between trees
• Infected firewood sometimes moves from yard to yard
• Older elms have no natural resistance

Cities like Denver, Boulder, Fort Collins, and Colorado Springs actively monitor DED, but private homeowners play a crucial role.

How Dutch Elm Disease Spreads

1. Elm Bark Beetles

The disease most commonly spreads when elm bark beetles feed or lay eggs on infected trees and then move to healthy ones. They carry fungal spores, which enter through feeding wounds.

Beetles in Colorado include:

• Native elm bark beetle
• European elm bark beetle

Both can spread DED.

2. Root Graft Transmission

Elm roots naturally reach outward and may physically graft together with neighboring elms. The disease can then move underground from one tree to another—even if you never see beetles.

This type of spread is especially common in older neighborhoods where rows of elms were planted at the same time.

3. Infected Wood

Logs, firewood, and storm debris from infected elms harbor both the fungus and beetle larvae. Bringing infected wood into a yard can start a new infestation.

Early Symptoms Homeowners Should Know

Dutch Elm Disease can progress slowly or quickly, depending on how it enters the tree. Recognizing symptoms early is critical.

Typical Signs Include:

• Wilting leaves in the upper canopy, often on one branch first
• Yellowing leaves that quickly turn brown
• Dead branches forming a distinct patch in the canopy
• Rapid leaf drop in mid-summer
• Discolored wood beneath the bark, showing brown streaks in annual rings
• Whole-tree wilt in severe or root-grafted infections

Symptoms usually appear in late spring through mid-summer.

If caught early, some trees can be treated before the disease spreads throughout the canopy.

Why Dutch Elm Disease Is So Serious

Once the fungus moves into the main trunk, the disease becomes extremely difficult to stop. The tree’s vascular system becomes blocked, causing rapid decline.

A large elm can go from a healthy canopy to complete death in just a few weeks, especially if infected through root grafts.

Even when the disease spreads more slowly, untreated infections eventually lead to:

• Loss of canopy
• Large branch dieback
• Structural hazards
• Tree failure

Because of safety risks and disease spread, removal is often required if the tree cannot be saved.

Management and Prevention Options

The best approach to Dutch Elm Disease is proactive: protect healthy elms before they become infected and act quickly if symptoms appear.

1. Professional Fungicide Injections

Healthy elms at risk can be protected with systemic fungicide injections. These treatments:

• Are applied directly into the trunk
• Move through the vascular system
• Block fungal growth if infection occurs
• Typically provide 2–3 years of protection

This is the most effective preventative tool, especially for high-value mature elms.

2. Sanitation and Removal

If a tree becomes infected:

• Prompt removal prevents beetles from spreading the fungus
• All infected wood must be properly disposed of or chipped
• Never store elm firewood unless fully debarked and dried

Leaving infected material on-site is a major risk.

3. Root Graft Disruption

To stop root spread:

• Arborists can sever underground root connections using specialized trenching
• This is especially useful where two elms are planted close together

Cutting root grafts can save a healthy elm even if its neighbor is infected.

4. Reduce Stress

Healthy trees are more resistant. Support elm health by:

• Watering deeply during dry spells
• Avoiding soil compaction near roots
• Not pruning during beetle flight season (typically spring–summer)
• Pruning dead wood only in dormant seasons
• Mulching around the base instead of turf contact

Stress makes infection worse.

Common Mistakes Homeowners Should Avoid

People often unknowingly increase the risk of Dutch Elm Disease:

• Storing elm firewood with bark attached
• Pruning in late spring or early summer
• Ignoring small patches of canopy wilt
• Letting infected trees stand for “shade”
• Assuming the tree will “recover on its own”
• Not hiring a qualified arborist to evaluate symptoms

DED requires professional diagnosis and management.

Is Your Elm Worth Saving?

In many cases, yes.

A mature elm is irreplaceable in terms of:

• Shade
• Property value
• Energy savings
• Aesthetic appeal
• Environmental benefits

Injection treatments and early intervention cost far less than removal and replacement. If you have a healthy elm in a neighborhood with other elms, preventive protection is strongly recommended.

When to Call an Arborist

You should contact a certified arborist if:

• You notice early canopy wilt
• A branch suddenly browns and dies mid-season
• Your neighborhood has a known DED case
• You’re considering preventive injections
• You recently bought property with large elms
• You have stored elm firewood on site

An arborist can test wood samples, confirm diagnosis, and create an action plan.

Final Thoughts

Dutch Elm Disease is devastating—but it’s also manageable. Many Colorado elms have survived because homeowners took action early. If you have a mature elm, consider it an investment worth protecting.

A quick consultation in spring can mean decades more of shade, beauty, and value.