This is a knock out. And I am not sure.. What's happening to this one

Oh and water at the base of the plant and not overhead. They don't like wet leaves as this contributes to blackspot.

Knockout:

The white areas on some leaves might be damage from sawfly larvae (rose slugs)...

Hard to tell for my eyes without a nice clear close-up pic of you leaves with dark spots BUT it could be blackspot or similar fungus disease... Some areas of the country have strains of blackspot spores that could attack Knockout roses. But KO does do well in many locations...

Be careful with homemade sprays as you could burn your leaves etc...

Jim.. I have tried home made baking soda solution.. It was somewhat in control with it. I went out if town for 4 days and it rained. I came back and saw a lot of BS.. Should I remove the stems also which r effected? For that I might have to prune the plant down to half.

Can you take clear closeup pics of the effected leaves so people maybe could help you figure this out???

I wouldn't remove any stems... Just leaves if they are truly infected with blackspot...

I can't tell from your pics exactly what those black spots are... (Me eyes are not the greatest anymore)

Jim.. Will this help?

It's just not clear enough to say. Some of it looks sort of like blackspot, but I can't see the edges of the spots. They should look rather like if you dropped black ink on a paper towel, and the edges sort of bleed. That would be blackspot. But some of the marks look like they end at the leaves in the vein. That would look more like downy mildew.

And some of the white spots look like rose slug damage -- but again, not clear enough to see.

Do you by chance own a flatbed scanner? If you do, you can put a leaf in a scanner, and scan at a high resolution, and have a GREAT image.

I don't have any camera other than my phone. I think it is black spot and sawfly larvae both. Powdery mildew may be. What should I spray now to save my roses?

Squish the sawfly larvae (or wash them away with a strong spray of water). I cannot confirm that this is blackspot. Maybe someone else can. If the leaves begin to turn yellow, remove them.

Are you getting a lot of rain? I don't really see mildew.

Black spot will bleed across all the veins, even the center one. Other spot diseases won't do that. But most fungicides will cover all the main ones, Read the label carefully and follow all the directions.

I think this is black spot and I saw the larvae when I was using this..

That will probably take care of it. You may still see some leaves spotting at first. Those are leaves that were already infected but not showing symptoms yet. Those will still spot and fall off but you've protected any more leaves from being infected. Follow all the directions carefully and spray again, when it says, to prevent it from coming back.

The product shown is neem oil with the azadirachtin removed. It will burn leaves in hot weather, as will baking soda--or even in moderate weather if the plants were not well hydrated before spraying. The large purple smears could be spray damage. Neither of these products gives very good control of spot diseases.

The bad foliage has several problems, not altogether clear what. As suggested above, the definite white spots are where rose slugs have peeled off the undersurface, leaving a translucent window. You have a very mild case so far. Just wipe the worms off the underside, or ignore it. I don't know what to make of the fine white speckling and abraded look in images 2 and 3. I suspect rose mosaic virus, which is incurable but not usually a crippling problem.

While some of the spots could be downy mildew symptoms, you can be sure that leaves with active DM will drop off the stems within a week or so. If spotted leaves do not drop, it isn't DM. Also DM usually attacks the newest foliage first.

I don't see any spots that look like blackspot (fringy or notched). Anyway, KO is virtually immune. However, KO commonly gets cercospora spot disease in my area. Some of the spots are probably that. It won't likely be a significant problem.

Finally, brown discs lining the leaf margin are a reliable sign of fertilizer burn.

Your rose may be suffering from too much TLC.