How to Manage Pests

Pests in Gardens and Landscapes

Pest identification and confirmation—Flatheaded borer

Common flatheaded borer species and damage

Wet spots on trunk
Wet spots on trunk

Flatheaded alder borer, bronze birch borer, twolined chestnut borer, bronze poplar borer, honeylocust borer Agrilus spp.

Flatheaded alder borers attack alders, bronze birch borers infest birch, twolined chestnut borers attack oak and chestnut, and bronze poplar borers infest Populus spp. Wet, dark, and gnarled growth often appears on the infested bark. Adult emergence holes, often D-shaped and about 0.13 inch in diameter, are left in bark.

Scattered dead patches
Scattered dead patches

Oak twig girdler Agrilus angelicus

Oak twig girdler is a flatheaded borer that attacks oaks in California. Infestations produce scattered patches of whitish brown leaves throughout the canopy. Leaves are dead, but have not been chewed and exhibit no surface scraping. A flattened, spiral tunnel, possibly containing dark brown frass and a larva, should be visible in twig girdler-infested oaks.

Borer beneath bark
Borer beneath bark

Pacific flatheaded borer and flatheaded appletree borer Chrysobothris spp.

Chrysobothris spp. are attracted to diseased, stressed, or injured trees of more than seventy species including ceanothus, cotoneaster, manzanita, maple, oak, rose, sycamore, and willow. Appletree borers are found throughout the United States; Pacific flatheaded borers occur only in the western states. Larvae excavate just beneath bark in the cambial area and may bore deeper into wood as they mature.


Statewide IPM Program, Agriculture and Natural Resources, University of California
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Agriculture and Natural Resources, University of California

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