How should I apply fertilizer to these Roses?

They need to be pruned. Get some air around them.
My momma, who was a master gardner, put crushed eggshells at the base of her roses.

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I'm trying to discourage growth at this point, so I'm gong to try a warm season cutback to put them in check.

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Just read this:
Overall, Knock Outs can be taken back by about 1/3 of their height, keeping in mind overall finished shape. Knock Outs tend to grow in phases (bloom - rest - bloom). If a mid-season trim is in order, it is best done following a blooming period while in the resting phase. Deadheading will also help to stimulate new bloom clusters and overall growth. Knock Outs tend to produce a lot of rose hips that inhibit flowering (triggering dormancy), so trimming these off will keep your Knock Out blooming.

I think I’ll try the mid season prune and then get them back in shape next February. But for now, we don’t mind the lush look and I think they’ll still flower pretty well.
Last year was spectacular.

Mine are around the mailbox so I have to get them in check or order a PO Box to get my mail.

I spray often. It’s been 4.5 years and I’ve never seen one

I spray minimally now. The knockouts needed too much babying in that regard. The oak leaf hydrangeas attract them some, but that is well after blooming. Phlox, jasmine, autumn climatis, lilies, and other natives I have around aren't appealing to them. They would absolutely devour the roses unless I sprayed regularly, which I dont want to do.