How to Manage Pests

Pests in Gardens and Landscapes

Treating alder and bronze birch borers

Thoroughly spraying foliage (where adults feed) and bark (whence adults emerge and where they land to lay eggs) with an insecticide such as permethrin can provide some control of flatheaded alder borer and the bronze birch borer. However, effective products labeled for trunk treatments are avilable only to licensed professionals. Well-timed insecticide sprays may reduce borer attacks, but do not substitute insecticide applications for proper cultural care or trees are still likely to die. If an application is planned, beginning the first of April inspect leaves for adult feeding holes and look for adults during mid- to late afternoon by examining foliage and by branch beating. Foliage and wood can be thoroughly sprayed with a persistent insecticide when adults are active, usually once about mid-April and again about 3 to 4 weeks later. Permethrin treatments are not effective against larvae beneath bark. Do not apply sprays to heavily damaged trees as they will die anyway and it may only exacerbate the problem as borers will emerge and attack nearby trees.

Soil drenches or injections with imidacloprid may provide some control if trees are relatively healthy. Remove adjacent seriously affected trees.

Look for borers
Look for borers and feeding holes on bark and foliage to time sprays


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