Weeping Willow Borer Infestation: Black Twig Borer

Three 9-year-old weeping willows near Sacramento show dieback; a broken branch revealed a white worm inside.

ID: Black Twig Borer (Xylosandrus compactus)

Tiny dark beetles bore into twigs, lay eggs, and cultivate fungus for larvae. Infested twigs die back. Over 224 plant hosts. Attacks healthy tissue.

Prune and destroy all infested twigs/branches.
Spray bifenthrin (Onyx) or imidacloprid (Merit) at 6-week intervals in spring.
Reduce fertilization—some evidence links high nitrogen to susceptibility.
Cold winters naturally suppress populations.

Act now; repeated applications needed for full control.

Trees: Weeping Willow Red Growths: Cankers, Galls, Borers - Multi-Threat Diagnosis; Weeping Willow Dead Branches: Normal Shading or Decline?; Defending Weeping Willows: Addressing HOA Concerns With Facts; Black Spots on Weeping Willow: Late-Season Leaf Spot Management; Willow Flea Beetles: Managing Black Beetles on Weeping Willow; Weeping Willow Scale and Woodpecker Holes: Diagnosis and Treatment; Black Walnut Twig Girdler: Large Branch Drop Explained; Weeping Willow Decline: Black Twig Borer Infestation; Weeping Willow Tree: Overview, History, and Care; When a Weeping Cherry Is Beyond Saving: Assessing Trunk Damage

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