Lilac-Ash Borer

Pest Description

• adults: 1 – 1 1/2 inches; black with yellow markings
• look like paper wasps
• larvae: up to 1 inch; pinkish-white with a brown head capsule

Host Plants, Diet & Damage

• ash; privet; lilac
• major pest of smaller ash trees in Utah
• larvae feed on cambium tissue and sapwood
• primarily found in the trunk and larger branches
• limb and canopy dieback are common
• leave irregularly round exit holes
• pupal skins extrude from exit holes (eventually fall out)

Biology, Life Cycle & Damaging Life Stage

• overwinter as larvae in chambers in the trunk
• adults are active late-April through late-July (northern Utah)
• eggs laid on bark
• larvae bore directly into cambium/sapwood layers to feed
• one generation per year
• larvae are the damaging stage

IPM Recommendations

• Monitor using delta traps and a clearwing moth pheromone lure starting in April.
• Hang monitors from branches at about shoulder height.
• Keep trees healthy and stress free.
• Do not plant ash (Fraxinus spp.) trees.
• Use a horticultural tree wrap to protect from winter sun.
• Use renewal pruning to remove older, more susceptible branches.
• Prior to moth flight, apply an insecticide (anthranilic diamide; pyrethroid) to stem and main scaffold branches.
• Systemic neonicitinoids are not effective against this insect.

For more information, see our Lilac-Ash Borer fact sheet.