It's a little hard for me to see, and I'm no expert, but it looks like sawfly to me. I get those too. I think the larvae are on the underside of the leaves and eat those lacey holes in them. Someone more experienced will come along shortly and confirm or deny my guess:) Lisa

They also call the larvae "Rose slugs". Lisa

To clarify, those spots on the leaves that look like maggots or larvae of some sort are neither. They are just dry (probably dead) spots on the leaves. I didn't turn the leaves over, but I did look closely at the tops...

I agree with Lisa but I see 2 things going on the first is as Lisa said sawfly larvae/rose slugs. Eggs are laid on the rose leaves by a special type of fly. When they hatch they are in the form of tiny little green worms. They can be found on the back of the rose leaves. When they first hatch they scrape the leaf surface. The more they eat the bigger they get. They can at that point eat holes in the leaves. When my roses are young I like to find and squish them since the rose really needs those leaves. Eventually they will grow and morph into the next stage of their life or something will eat them.

The next thing is a disease issue but I am unable to see the spots well enough to tell what it is. A fungicide wether organic or chemical will help with the spots. Try to be sure that what you use does not include an insecticide and is as earth friendly as possible.

I'm guessing that NEO stands for North East Oregon. Maybe someone from that area will see this and help you out.

Insects AND disease? I thought Knockout roses were supposed to be virtually disease free?

If there are a ton of tiny little green worms eating my leaves, shouldn't I be using an insecticide to get rid of them?

And, sorry - NEO stands for North East Ohio...Sometimes I forget that people outside of my area don't just know what NEO means :)

I'll get up to the nursery where I bought these with a bunch of pictures and maybe some leaves (in a baggy so I don't infect the nursery) and see what they say.

Yep, rose slugs. Turn over leaves and you'll see the little green buggers. I am no longer squeamish- I happily squish them by hand. Lots of good bugs prey on them- if you spray you'll kill the "good guys" too. They have a pretty short window where they do this (there's another bristly kind that eats for a longer window i think).