Rose bushes

Question: All of the rose bushes in my yard have leaves with holes all over them. It's affected every single bush in my yard. I don't see any pests on them anywhere at any time yet almost all the leaves are affected by this. The only thing that I've noticed is an abnormally large amount of flies. I live in a regular Suburban neighborhood with no livestock nearby. I pick up after my dogs once or twice a day so I know that's not it. Additionally the Flies seem to be a little different than common house flies that I usually see every year. Any help is appreciated.

responder: Weld County Colorado Master Gardeners Replied July 26, 2023, 5:59 PM EDT
response: I think I've almost identified your critter.  As soon as we correctly identify the pest, we can find a treatment that will work.  Ms. Lascor, earlier this summer did you see slugs on the underside of the rose bush leaves?  Did you see something like these guys?    https://blogs.k-state.edu/kansasbugs/2017/05/26/rose-sawflies-2/  https://extension.unh.edu/blog/2019/06/whats-eating-leaves-my-roses  I have also sent your photos to a Colorado State University Extension rose expert for identification.  But your description of the immature slug would help immensely.  Hope to hear from you soon!  Sue Weld County Colorado Master Gardener  Hope to hear from you soon!

responder: The Question Asker Replied July 26, 2023, 8:20 PM EDT
response: Hello, thank you so much for responding and for looking into this. I did not notice any of these slugs on my leaves this year. I also haven't noticed any pests whatsoever prior or currently. The only thing was the abundance of those different kind of flies. I'm attaching a couple more pictures of the leaves.  On Wed, Jul 26, 2023, 3:59 PM Ask Extension <<personal data hidden>> wrote:

responder: Weld County Colorado Master Gardeners Replied July 27, 2023, 4:01 PM EDT
response: Ms. Lascor,  When I first read your query and took a quick look at the photos of damage you sent, I thought it might be an infestation of Japanese beetles. (https://ask2.extension.org/file.php?key=dfbcgov_x84g6lnrbuvkmmzlzkjo3luk&expires=<personal data hidden>&signature=0888bf4b4f07fd9619ecad6e76fb1708ca95d037&id=1761162) But you’re right, these bronze critters look like flies, not beetles.    The photo you took of the insect on one of your white roses enabled us to identify the pest. Well done!  It’s confusing because the critter has many names. The larvae are called “Rose Slugs.” They are known as “Rose Sawflies” when people see them as something that looks like a mature adult fly. However, these things are not flies (Diptera), but wasps (Hymenoptera). The good news is that these wasps do not sting people.   That’s all very interesting, Ms. Lascor, but I get the feeling that you want these pests GONE. Right? On your plants, have you seen the slugs that turn into sawflies? It is suggested that you hose them off.  I sent you these two websites earlier:  https://blogs.k-state.edu/kansasbugs/2017/05/26/rose-sawflies-2/  https://extension.unh.edu/blog/2019/06/whats-eating-leaves-my-roses  Late last night, I got an email back from a Larimer County Master Gardener who knows more about roses than I ever will. Roger said to inspect the underside of the rose leaves to look for crawling larvae to be sure.   He added sawfly will lay eggs several times a season, “So if you don’t see larvae now, you probably will in a few more days.”  He said to spray the pesticide on the underside of the leaves. Why? #1, that’s where the larvae live and cause damage. #2, if you spray on top of the leaf, you will affect the adult saw flies. However, the treatment will kill other pollinators as well.   The only two research-based resources I’ve found for you on Integrated Pest Management (IPM) that discuss specific pesticides that work against “Rose Sawflies” are: https://ipm.ucanr.edu/PMG/GARDEN/PLANTS/INVERT/sawflies.html and https://www.rhs.org.uk/biodiversity/rose-slug-sawfly-or-slugworm  One more thought: Might some of the damage be due to the grasshoppers so many gardeners are seeing now? https://planttalk.colostate.edu/topics/insects-diseases/1447-grasshoppers/  Hope this helps!  Sue  Weld County Colorado Master Gardener