CO-Horts Blog

Monday, March 27, 2017

Rose Slugs or Lace Bugs - That is the Question

 Posted by Mary Small, CSU Extension Master Gardener Coordinator

With that title, you might wonder about me – yes, I’m aware it’s still March! And dealing with those guys is a bit down the road yet. But here’s the deal:
I recently returned from a family gathering in Missouri. While there I was asked about a plant problem. I’m usually pretty wishy-washy about identifying out of state plant problems because conditions and pests can be so different. But I fearlessly dove in. It went something like this.

FM (Family Member): What would make the leaves on a rose look lacy? Do you think the recent cold weather would kill it altogether? (I determined she meant would the cold have killed the overwintering stages.)
Me: (visibly annoying the FM by not giving an immediate, decisive answer):  It sounds like rose slug to me, but I don’t know what pests you have here. I really need to figure out what the pest is first.
 Lace bug damage, Whitney Cranshaw, CSU Extension
FM: The garden center said it was lacebug. They feed on the leaf undersides – and it’s hard to treat there, so I’m not sure I killed them.
Me: (While hastily looking up symptoms of lace bug damage on that state’s Extension web site): Did the garden center staff person see the damage?
FM: No, but that’s what they thought it was.
Me: Well, here’s a picture of lacebug damage. Is this what it looked like?
FM (looking at the pictures on my phone): Well, not quite, well, maybe. Maybe there are still some leaves under the roses that you can look at.
Me: (Trudge outside, poke around under the rosebushes and find some leaves with- ta da- pretty heavy-duty rose slug damage. Go inside and show my “find”.) “Is this the damage you were seeing?”
FM: Yes, that’s it!
Image result for rose slug damage
Rose slug damage, Ask An Expert
Me: Okay, you have rose slugs, not lacebugs.
FM: Will the pesticide in the garage kill them?
Me: Trudge out to the garage – mercifully there is only one pesticide to examine. It contains spinosad and roses are on the label. Woo hoo – the FM’s good to go with their annihilation plans.
Then the pesky overwintering question- and I found the answer in a research-based source - “When spraying, be sure to spray both sides of the leaf and the ground below the plant as the larvae pupate in the soil prior to overwintering.” 
Having not taken some of these steps, the FM will need to do a bit of scouting this spring for the newly emerged larvae. Then treat, continue to scout and possibly re-treat.
This late winter- time exchange reminded me the importance of one of those early diagnostic steps – “examine the plant”.  And while I kinda doubted lacebug was the culprit – I checked my research-based resources to confirm. This story will come in very handy shortly when I teach our Master Gardeners about the diagnostic process.
And now I better send off the information about rose slugs to the FM.


  1. Thank you, Mary. I appreciate seeing your dialog (I am a Colorado Master Gardener Apprentice) and it helps to be reminded via your real life example above of what you taught us in class.

  2. Mary:
    This was a delightful family reunion story, with your true-to-encounter asides, until I realized that I wasn't clear on lacebugs. I am now. Lacewings have no place here! I enjoyed and learned another facet of diagnostics. Many thanks.