Yes, you can cut them back by a third, but I would wait until this flush of bloom is over.

If you look down the pages for threads with titles like "something is eating my roses," you will find discussions of rose slug, a type of sawfly larva that is probably the culprit. Look underneath the leaves.

In the Spring when you first start seeing damage that's when to start spraying Safer insecticide soap OR Spinosad.
Then repeat according to directions...
I spray in the evening after sun goes down.
The leaves do not burn that way and it seems to make the sprays more effective. Slower drying time maybe?

This post was edited by jim1961 on Mon, Jun 3, 13 at 22:50

The rose slugs here right now are still tiny. (1/4 inch)
But still being very destructive. They will grow to about
3/4" - 1 " later in the season.
I'm not sure about your part of PA but here Rose Slugs are here from May until November+...
The Rose Slugs we have hang out on top of the leaves and on the underside of the leaves...
Ours are greenish in color with Orange heads and I seen some with black heads...
I wasn't going to spray this year but changed my mind when I seen all that damage yesterday and its only early June...
So this evening I sprayed the top and bottom of all the leaves and canes on every rose with Safer Insecticide Soap.
Our Ko's have some Aphids too and the soap helps control them also...

Before I spray our rose bush leaves I water the bush really good the day before... (Water the ground)

This post was edited by jim1961 on Mon, Jun 3, 13 at 22:48

Thanks folks. I suppose I let my guard down because last year I had no problem with insects until later in the summer. I was floored when I saw the damage that was done in just a few days (it seems). I looked over the plants and I swear I can't see any slugs, bugs, or worms - the leaves just look like lace at this point. I did spray with an insecticidal soap (just to keep future damage down), but as soon as these blooms fade, I'm going to cut these way back. I know they'll look hideous for a while, but hopefully they'll bounce back. By the way, once I do cut them back, should I give them a good dose of Miracle-Gro or some other fertilizer? Thanks for all your help.

Heres a pic of our Rose Slugs. They have turned a white
color from being sprayed with safers insecticide soap...
These guys are still little... Our guys can be found on top of the leaves but they also hang out on the UNDERSIDE of leaves...

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There are two or three kinds of rose slugs, but the ones in my garden are only on the underside of the leaves. If I don't find any there, it's because the wasps have picked them off. Usually the predators get on top of the rose slugs after a while and they are not a continuing problem--but in some gardens they can be. I wouldn't use spinosad on them for fear of hurting the predators. For soap to be effective, you have to coat the underside of the leaves where there is feeding damage, and it's about as easy to wipe the worms off with your thumb.