One heck of a case of rose slugs/sawfly larvae or curled rose slug. The curled rose slug is the largest and can eat a lot. Depending on where you are from there may be other caterpillar types involved as well. I always hunt them down and squish. Neem oil may help but I don't like to use it in heat. Perhaps others will chime in on how to treat.

The rose slugs I know very well, arghh, I hate them! I just crush whatever is underside the leaves with my fingers, using gloves of course in case there's any other catterpillars that can cause rashes. I also check if there's no ladybugs on the foliage before I pinch the maleficent ones.

Yep bad case of Rose Slugs...Green looking worms usually found on the underside of rose leaves...They can be very tiny or up to a inch long...

Pick them off bush & kill...Least toxic spray is safers insect killing soap...Spinosad real effective but can kill bees...

As soon as you first start seeing damaged leaves in the Springtime is the time to take action so it doesn't get bad...

I'd like to add this in case anyone is interested. The european sawfly has one generation a year. In early spring the adult sawfly emerges and lays its eggs on the rose leaves. In a few weeks the larvae emerge and begin to feed on the leaves. If we can't find and eliminate them or a predator doesn't eat them. After about a month they will fall to the ground where they stay until the following spring. Of course there are a few other species of sawfly. The new bristly sawfly can have up to six generations in a year. Like a rose grower doesn't have enough problems to deal with.

I usually fold the leaf over the sawfly and squish. But, like Jim said - you should take action as soon as you see a tiny hole.

Carol