PestMedium Severity

Cottonwood Longhorned Borer

Plectrodera scalator

A large longhorned beetle that attacks cottonwood, poplar, aspen, and willow trees, primarily at the base or below ground line. Adults are 1-1.5 inches long, shiny black with cream-colored markings. Extensive larval mining can girdle young trees and create structural weakness.

Peak Season: Adult emergence: Mid-summer peak activityEgg laying: August and SeptemberLarval development: 1-2 years within treesPupation: April to June (3 weeks duration)Most vulnerable period: When larvae are actively feeding in fall
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Cottonwood longhorned borer adult and damage

Identification & Symptoms

What to Look For

Light brown, fibrous frass ejected from bark openings
Frass accumulating in piles at tree base
Mining damage visible in bark and cambium
Tunnels through sapwood extending into heartwood
Exit holes where adults have emerged
Root collar and roots riddled with larval tunnels

Potential Damage

Girdling of stems and roots in young trees
Extensive tunneling weakening tree structure
Reduced water and nutrient transport
Increased susceptibility to wind damage
Tree mortality in severely infested specimens
Economic losses in commercial poplar plantations

Lifecycle

Adults emerge in mid-summer, feed briefly, then mate and lay eggs in bark pits at tree bases. Eggs hatch in 16-18 days. Larvae bore downward in inner bark, entering large roots by autumn. Development takes 1-2 years. Pupation occurs in spring galleries for about 3 weeks.

Professional Treatment Approach

1

Systemic Imisol treatments for protection of high-value trees

2

Imicide applications targeting adult emergence periods

3

Focus treatments on root collar and lower trunk areas

4

Monitor for frass production indicating active infestations

5

Remove and destroy heavily infested trees to reduce breeding sites

Recommended Mauget Products

Imisol

Professional-grade treatment specifically effective against cottonwood longhorned borer.

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Imicide

Professional-grade treatment specifically effective against cottonwood longhorned borer.

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