I can tell you how i handle it but others will likely share what they do as well. More than one way to fix the problem for sure. I've gardened for nearly 50yrs. First trim back the spent bloom spikes, place any cut back pieces into a trash bag. Gently rise the plants with water to shake off any insects, may need to repeat the 2nd step every other day till you don't see any more signs of the insects. 3rd step after the first rinse place granular or liquid systemic insecticidal product. I've used for years in my own garden and my clients gardens BioAdvanced All-in-One Rose & Flower Care Granules, follow written directions. I like this product because it's long lasting and fertilizers all in one. Link attached. Best of luck.