Cottonwood Borer

Q: What trees do cottonwood borers attack?

Cottonwood (Populusspecies) and willow (Salixspecies) exclusively — they're specialist borers. If you don't have these trees, you won't have cottonwood borers.

🪲 Cottonwood Borer

Plectrodera scalator · Coleoptera: Cerambycidae

The cottonwood borer is one of the most visually striking beetles in North America — and one of the largest. Despite its size, it's often overlooked because adults emerge briefly and adults are rarely seen.

BeetleTree PestCerambycidaeCottonwoodRoot BorerLonghorn

🔬

PestControlBasics Editorial Team

Reviewed by Derek Giordano · Updated 2026

Illustrated identification guide — PestControlBasics.com

🔍 Identification

Adults: 25-40mm — largest North American cerambycid (longhorn beetle); striking black and white pattern; very long antennae (often as long as or longer than the body). Found on cottonwood and willow trees July-August. Difficult to miss when adults are present.

🧬 Biology & Behavior

Females lay eggs at the base of cottonwood and willow trees. Larvae bore into the roots and root collar — not the trunk above ground. Larval period: 2 years in roots. Pupation occurs in the root collar or base of the tree. Damage from root feeding weakens trees and makes them susceptible to windthrow.

⚠️ Damage & Health Risk

Root feeding weakens tree structure; girdling at root collar can kill trees over multiple larval generations; entry wounds at root collar create entry points for pathogens; heavily infested young trees can be killed; landscape cottonwoods most at risk in irrigated areas.

🔧 DIY Treatment

Apply carbaryl or permethrin spray to the trunk base and root flare in July-August when adult females are laying eggs. Repeat application 2-3 weeks later. This prevents new egg-laying but doesn't affect existing larvae. Reduce water stress on trees — vigorous trees resist borer damage better.

👷 When to Call a Pro

For high-value trees, certified arborist assessment and trunk injection of emamectin benzoate provides systemic protection against new larval establishment.

❓ FAQ

Is the cottonwood borer dangerous?

No — the cottonwood borer is entirely harmless to humans. Adults can startle people with their large size but cannot bite effectively. They're specialized tree pests with no interest in people.

What trees do cottonwood borers attack?

Cottonwood (Populus species) and willow (Salix species) exclusively — they're specialist borers. If you don't have these trees, you won't have cottonwood borers.

Factor	Details
U.S. Range	All or most U.S. states
Regional Detail	Distribution varies — consult your local extension service for regional prevalence data.

Factor

Details

U.S. Range

All or most U.S. states

Regional Detail

Distribution varies — consult your local extension service for regional prevalence data.

📅 Treatment Timing Guide

Treating at the right time dramatically improves results. Pest control timed to the life cycle uses less product and achieves better long-term control.

Period	Action
Spring	Inspection and perimeter treatment before pest season starts.
Summer	Active monitoring and targeted treatments as needed.
Fall	Preventive treatment before overwintering pests seek entry.

Period

Action

Spring

Inspection and perimeter treatment before pest season starts.

Summer

Active monitoring and targeted treatments as needed.

Fall

Preventive treatment before overwintering pests seek entry.

💰 Professional Treatment Costs

Service Type	DIY Cost	Professional Cost
Initial inspection	Free (self-inspect)	$75–$150 (often credited to treatment)
One-time treatment	$30–$100 in materials	$150–$500
Annual service contract	N/A	$400–$900/year
Severe infestation	Often ineffective alone	$500–$2,500+

Service Type

DIY Cost

Professional Cost

Initial inspection

Free (self-inspect)

$75–$150 (often credited to treatment)

One-time treatment

$30–$100 in materials

$150–$500

Annual service contract

N/A

$400–$900/year

Severe infestation

Often ineffective alone

$500–$2,500+

Prices vary by region, property size, and infestation severity.

❓ Common Questions About 🪲 Cottonwood Borer

How do I confirm I actually have this pest (not something similar)?

The most reliable confirmation is a physical specimen — capture one and compare to reference images on this page. For cryptic pests (bed bugs, termites), look for secondary signs: frass, shed skins, mud tubes, or bites with a specific pattern. When uncertain, a professional inspection is faster than months of misidentification.

Can I treat this myself or do I need a professional?

DIY is effective for small, accessible infestations caught early. Professionals are worth the cost when: the infestation is inside wall voids or structural elements, multiple rooms are affected, you have health-risk pests (hantavirus, venomous species), or DIY has already failed twice.

How long until the infestation is completely gone?

Expect 3–8 weeks for most infestations with proper treatment. Insects with dormant life stages (pupae, eggs) extend the timeline because those stages are impervious to most insecticides. Follow-up treatments at 2 and 4 weeks catch each new cohort as they emerge.

What's the most common mistake people make treating this pest?

Treating only the visible pest population while ignoring the harborage site, entry point, or breeding location. Killing adults provides temporary relief but the population rebuilds from hidden egg cases, pupae, or new arrivals through unaddressed entry points.