Friday, April 11, 2014

Lilac Ash Borer Does Not Equal Emerald Ash Borer by Mary Small

Lilac Ash Borer Damage in Ash
I was recently sent this photo and asked if I thought this could be emerald ash borer damage. Apparently a lot of ash trees in the neighborhood have similar injury.
Note D-shaped holes
One hole looks like a D, which could indicate a flatheaded borer such as emerald ash borer. (But flatheaded apple tree borers can also infest stressed ash.) Consider too, that lilac ash borer creates irregularly round exit holes and the rest of the holes in the picture are round-ish. The D shaped hole also is ragged around the edge, which is not typical of the flatheaded borers mentioned above.
 So how can you tell (without tearing the bark off) which of the insects might be damaging your ash tree?Lilac ash borer holes are round-ish and about ¼-3/8 inch wide; Emerald Ash borer are D-shaped and about 1/8 inch wide. 
  • Lilac ash borer holes extend deep into the wood and you can poke a wire into it quite a distance; you can’t do that with emerald ash borer because they feed right under the bark.
  • Lilac ash borer adults emerge from May through early June. Emerald ash borer is expected to emerge in mid May through early July. Lilac ash borers frequently leave behind their pupal skins on the bark as they emerge, emerald ash borers don’t.
  • Dead branches and stems are common for both pests; typically lilac ash borers push a sawdust- like material (frass) from their entrance holes before they emerge. It can accumulate at the base of the tree or in crevices on the bark.  Emerald ash borer has no exterior frass associated with it.
  • Repeated infestations of lilac ash borer cause swellings and a gnarled appearance to trunks and infested branches. Emerald Ash Borer does not cause this damage.

  • Lilac Ash Borer Damage in Ash

    If you think you have Emerald Ash Borer in your ash trees, or if you have any questions or concerns, or would like additional information, please contact the Colorado Department of Agriculture at 888-248-5535 or email