WSU Extension

Hortsense

Caption: ash borer pupal 'skeleton'
Photo by: A.L. Antonelli
  
print version| pdf version| email url    

Mountain Ash : Ash borer
(revision date: 4/28/2014)


Biology
The ash borer, also known as the lilac borer, is a member of the clearwing moth family. The adults of many clearwing moths mimic yellowjackets or paper wasps. The larvae of this moth cause damage to ash, lilac, and privet. The larvae tunnel in the bark of stems (trunk) and branches causing a gradual weakening of the plant. Other than emergence holes, one can determine the pests' presence by the pupal skeletons attached to the bark at the emergence sites. There is usually only one generation per year. However, a two-year cycle can occur in the northern part of its range. Adult numbers usually peak in May or June and females lay their eggs singly in bark crevices where they soon hatch and burrow their way into the phloem tissue and continue feeding. Emerging full-grown larvae produce a round hole about 1/16 inch in diameter. Urban, open grown trees are highly susceptible to infestation.
Management Options

Non-Chemical Management
  • There is little that can be done after trees have been attacked.
  • Since eggs are almost always laid in or near wounds, avoid pruning when moths are present.
Select non-chemical management options as your first choice!

Chemical Management


None recommended

Images
    - hide images

+ Show larger images

 
Caption: ash borer pupal 'skeleton'
Photo by: A.L. Antonelli