Experts and BHG readers answer.
Black spot on knock-out roses
Knock-out roses are resistant to most rose troubles, but resistance isn't enough when the conditions are just right for a disease or insect attack. The holes in your leaves may be leaf-cutter bees, beetles or slugs. Don't use an insecticide for any of these, but if you see beetles or slugs on the foliage, pick them off by hand and destroy them. The white spots you describe don't sound like aphids. Aphids are tiny but generally large enough that you can see their legs and antennae with your bare eyes. To control the black spot, prune off the worst of it. Remove any fallen leaves that will harbor spores. Mulch under your plants and water in the mornings so the foliage will dry quickly. And finally, you can use a fungicide like copper sulfate. I know that with knock-out roses, you thought you could avoid using chemicals, and it's possible that the other steps I've listed will be enough to reduce the black spot substantially without chemicals. Consider the fungicide optional.