You can try BurnOut or Scythe, both organically approved herbicides, after digging out the roses and transplanting. Even with Round up or other chemical herbicides, you must dig up what you can, dispose of the weeds and their roots, spray, wait, spray again, wait, perhaps spray a 3rd time. Same for the acetic acid(vinegar-based) organic herbicides.

When a bed is badly infested, a combination of mechanical and chemical methods works best: removal by hand, smothering with sheets of cardboard, cutting back as soon as a shoot appears, sifting soil thru a screen to remove all pieces of root, the repeated use of herbicides (hopefully organic ones), solarizing the soil by putting down black plastic and leaving it over the soil for a spring and summer season, and so on.

Removal of weed infested soil and relacement with fresh topsoil and amendments, as in raised beds, is also an option.

Basically, it is a bit of work.

I agree with Ginger. I'd like to add a warning (from bitter experience): if you don't do the work properly now, you will wage an endless, discouraging battle against weeds for ever. Take Ginger's excellent advice about clearing the ground, be patient, and eventually you will be so glad you did.