Pretty and Devastating.

Iris Borer

Macronoctua onusta


I found this picture on a card where it had been residing for 6 months - not sure how I missed it, but c'est la vie. But finding it almost meant that I had now identify it.


It turns out that while it's an attractive moth, it's not exactly something we want in our yard - Iris borers lay eggs on dead/dying iris leaves in the fall, where the eggs overwinter. They then bore through the dead leaves into the fresh shoots. Eventually, they will bore into the rhizomes - and the iris will die from the damage or opportunistic bacteria infections that are common with iris borer infestations.


One way to know if you have an problem is to look for tracks along your iris leaves - although that's not an absolute sign. If you do see some, hold the leaves up to light - if you see little worms, you've got the larva. Luckily, they can be treated with an application of nematodes available at garden shops. Unfortunately, signs can be missed until they are already in your roots, meaning damage can become extensive before you see it. Best defense - cut off and dispose of your dead iris leaves in the early fall. More info here.

Bob Gutowski faved this
  • Siobhan PRO 7y

    Beautiful macro! Great colors, but yeah, sounds like I really don't want them around my Irises. Thanks for all the info, I'll have to keep a look out for these.
  • Doug 7y

    Very interesting Marty
  • Pamela Reid 7y

    Great shot Marty! I always wondered what these critters looked like. I've seen beds of Iris disappear from their work. I'll be on the look out now.
  • Anita Gould PRO 6y

    Evil indeed! I remember instructions never to compost iris leaves so as not to attract & feed these.
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Taken on September 24, 2007
  • 70.0-300.0 mm f/4.0-5.6
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