knock out roses have little white spots
The white spots are on the roses, in addition some leaves are turning red. Is that something I need to be concerned about?
The red leaves can mean just new foliage coming out. If it is mottled looking and the foliage looks out of character with the rest of the bush, this may be something to keep an eye on as it could be a virus called Rose Rosette and there is no cure for it. If the bushes get it, the best thing is to destroy them and buy new rosebushes. The white spots may be mealy bugs.
Here are a couple links to articles for you: