PestHigh Severity

Flatheaded Borer

Chrysobothris californica

Small metallic beetles whose larvae create irregular tunnels in the inner bark and cambium of stressed trees. Adults are flattened in appearance, and larvae have distinctive broad, segmented heads that are three times wider than their bodies.

Peak Season: Adults emerge spring through summer. Peak activity during warm months. Larval development occurs over multiple years.
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Flatheaded borer damage showing characteristic galleries and emergence holes

Identification & Symptoms

What to Look For

Irregular tunnels in inner phloem partially filled with powdery frass
Extensive mining of bark and cambium
Potential girdling of young trees
Tunnels through sapwood and into heartwood
Fine powdery boring dust around entry points
Branch dieback and tree decline

Potential Damage

Girdling of stems and roots in young trees
Disruption of nutrient and water transport
Structural weakening from tunneling
Secondary pathogen invasion through wounds
Potential tree mortality in stressed trees
Reduced timber value from galleries

Lifecycle

Adults emerge from pupal cells in spring or summer, feed briefly, mate, and lay eggs in bark crevices. Eggs hatch in 10-50 days. Larvae mine for several years before pupating. Usually one generation every 1-2 years. Pupal stage lasts about a month, but may overwinter. Adults may overwinter in pupal cells or hibernate before emerging. Adults die within 1-2 months after emergence.

Professional Treatment Approach

1

Apply Imisol as preventive treatment to high-value trees

2

Use Imicide for direct treatment of infested trees

3

Maintain tree health with Arborfos to reduce susceptibility

4

Avoid wounding trees during construction or maintenance

5

Remove and destroy heavily infested material

6

Address underlying stress factors (drought, compaction, injuries)

Recommended Mauget Products

Imisol

Professional-grade treatment specifically effective against flatheaded borer.

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Imicide

Professional-grade treatment specifically effective against flatheaded borer.

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Arborfos

Professional-grade treatment specifically effective against flatheaded borer.

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Need Professional Diagnosis?

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