Japanese Beetle Populations on the Rise in Colorado

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

In recent years, homeowners across the Front Range—from Fort Collins down through Denver and into Colorado Springs—have seen a sharp increase in Japanese beetles. Their shiny green and bronze bodies may look harmless, but their feeding behavior can strip trees, shrubs, and gardens in a matter of weeks. As certified arborists, we’ve seen what untreated infestations can do: devastated roses, skeletonized linden leaves, and stressed trees heading into winter with less stored energy.

Understanding this pest is the first step to protecting your landscape.

What are Japanese Beetles?

The Japanese beetle (Popillia japonica) is an invasive insect from Asia. It was first detected in the United States over a century ago and has steadily spread westward. For a long time, Colorado’s dry climate slowed its expansion—but irrigation and urban landscaping have created perfect conditions along the Front Range.

Two Life Stages Homeowners Need to Know

Japanese beetles cause damage in two ways:

1. Adult beetles (June–August)
   • Feed on leaves, flowers, and fruit of over 300 plant species
   • Cause rapid defoliation through “skeletonizing” leaves

1. Larvae (grubs) (fall–spring)

1. • Live in turfgrass soil
   • Feed on grass roots, causing brown patches and turf die-off

This means Japanese beetles impact both trees and lawns.

Why Japanese Beetles Are Increasing on the Front Range

For decades, Japanese beetles were rare in Colorado. Now, fully established populations exist in many cities. Why the change?

Several factors have created ideal conditions:

1. Irrigation and Managed Landscapes

Beetles thrive in:

• Moist, well-irrigated lawns
• Rich, amended soils
• Frequent watering cycles

These conditions weren’t common historically but are standard in many neighborhoods today.

2. Mild Winters

Cold winters used to limit egg and grub survival. With warmer soil temperatures:

• Grubs overwinter successfully
• Populations rise each season

3. Transportation and Movement

Beetle eggs and grubs travel in:

• Sod and nursery plants
• Soil around roots
• Yard waste and compost

As landscaping materials move, so do beetles.

4. Limited Natural Predators

While birds and other insects will eat Japanese beetles, there are no strong natural predators controlling their population in Colorado.

What Japanese Beetle Damage Looks Like

Recognizing the signs early allows you to take action before widespread damage occurs.

On Trees and Shrubs

• Leaves look “skeletonized”—veins remain, leaf surface is gone
• Damage often starts at the top and outer branches
• Beetles cluster in groups, especially when feeding
• Flowers are eaten entirely, especially roses
• Lindens, birch, crabapples, and fruit trees show heavy damage

Beetles prefer sunny areas of the plant first.

In Lawns

Grub damage becomes visible in late summer and early fall:

• Brown patches that don’t respond to watering
• Soft, spongy turf that lifts like carpet
• Wildlife digging (skunks, raccoons) hunting for grubs

This damage often appears where adults laid eggs during the summer.

High-Risk Trees and Plants on the Front Range

Japanese beetles feed on over 300 species, but some are clear favorites:

Commonly Attacked Trees

• Linden (Basswood)
• Birch
• Crabapple
• Purple-leaf plum
• Apple and pear
• Fruit trees (peach, cherry)
• Japanese maples (rare but possible)

Shrubs & Ornamentals

• Roses (most preferred plant)
• Virginia creeper
• Grape vines
• Serviceberry
• Raspberry
• Hibiscus
• Various ornamental shrubs

If you have many of these plants, beetles will be attracted each year.

Why This Damage Matters

Japanese beetle feeding isn’t just cosmetic—repeated defoliation harms tree health.

Impact on Tree Health

• Reduces photosynthesis
• Weakens trees going into winter
• Increases vulnerability to drought stress
• Slows growth
• Can lead to dieback in young or stressed trees

A healthy, mature tree can survive one season of feeding—but year after year of damage has a compounding effect.

Management and Prevention Strategies

There is no single “silver bullet” for Japanese beetles. Effective management on the Front Range requires a combination of strategies.

Here’s what arborists recommend:

1. Improve Plant Health

Healthy plants tolerate feeding better. Support your trees with:

• Proper watering cycles
• Mulched root zones
• Correct pruning (timing matters)
• Soil amendments when necessary
• Fertilizing responsibly (not overusing nitrogen)

Stressed trees suffer more from beetle feeding.

2. Manual Removal

It may sound simple, but hand removal works:

• Drop beetles into soapy water early in the morning
• Reduces feeding and reproduction
• Breaks the cycle in early outbreaks

Early morning is best—beetles are sluggish from cool temperatures.

3. Avoid Attracting More Beetles

Beetles release pheromones that attract others. When a few arrive, many follow.

• Removing early clusters reduces attraction
• Consider planting less-preferred species
• Avoid installing new high-risk ornamentals in heavy beetle areas

Beetle traps often increase damage by drawing beetles to your yard—avoid them.

4. Professional Treatment Options

Arborists may recommend treatment for high-value trees, especially lindens, mature crabapples, and ornamental landscapes.

Options include:

• Systemic insect treatments (applied to soil or trunk in spring)
• Targeted foliar sprays during peak feeding
• Turf treatments to reduce grub populations

Timing is critical. Treating too late will not protect foliage that is already being eaten.

5. Homeowner Turf Care

To reduce grub populations:

• Avoid overwatering lawns
• Aerate to improve root health
• Reduce excessive thatch
• Consider turfgrass that doesn’t require constant irrigation

Healthy turf is less attractive for egg-laying females.

Long-Term Strategy: Plant Selection

If you’ve struggled with Japanese beetles for several years, it may be time to rethink your plant choices.

Less-Preferred Trees

• Hackberry
• Honeylocust
• Kentucky coffeetree
• Bur oak
• Aspen
• Spruce (damage limited)
• Elm (Dutch elm disease resistant cultivars)

Replacing heavily damaged species can reduce yearly outbreaks.

Front Range-Specific Recommendations

Because conditions vary from the foothills to the plains, consider these local insights:

• Urban neighborhoods with heavy irrigation see the highest infestations
• Areas near parks or older neighborhoods with roses are hotspots
• Colorado Springs is seeing rapid population growth due to milder winters
• Boulder and Denver Metro are seeing established populations that grow every year
• Foothill properties have fewer beetles due to drier soil and less irrigated turf
• HOA landscaping often unintentionally creates ideal beetle habitats

Every property is different. Local microclimates matter.

When to Call an Arborist

Call a certified arborist if:

• Your tree or shrubs are showing significant leaf loss
• You’ve seen beetles for multiple years in a row
• A young tree has 30–50% defoliation
• You’re planning to plant new high-risk ornamentals
• You want a professional treatment plan with proper timing

Early planning—before June—offers the best control.

Final Thoughts

Japanese beetles are here to stay on the Colorado Front Range. Homeowners can no longer rely on the climate alone to prevent infestations. The key to protecting your trees and landscape is a combination of smart planting choices, early intervention, and consistent care.

Healthy plants, informed homeowners, and experienced arborists make the best defense.

If you’d like help assessing your risk or developing a preventative plan before beetles emerge this summer, reach out to a certified arborist. We’re here to help keep your trees thriving in the face of changing conditions across Colorado.