Lilac Dying Branch by Branch: Lilac Borer Infestation

Lilac in eastern Iowa dies one branch at a time: leaves turn crispy brown, no visible chewing. Owner asks cause.

Diagnosis: Lilac Borer (Podosesia syringae)

Symptoms match:

• Sudden wilting of canes/stems.
• Swollen base, bark separating from wood.
• Fine sawdust-like frass around holes.

Life Cycle

• Larvae overwinter in wood; pupate spring.
• Adult moths (clear-winged, wasp-like) emerge mid-April to early July.
• Eggs laid in bark cracks; hatch in 10–14 days.
• Larvae bore into wood; one generation/year.

Control

• Bayer Advanced Tree & Shrub Insecticide (imidacloprid) soil drench.
• Contact certified arborist for additional options.
• Read all labels; wear protection; store safely.