For me what finally did the trick was to be very consistent. Spray every 3 days - very thoroughly; no excuses, don't put spraying off for even a day. Do this at least 4 times... maybe 5 or 6 if it's really bad. I tried a lot of things and they kept returning. I don't think WHAT I used was the trick, just how I used it. Doing it every three days repeatedly for a decent period of time will get them as they hatch - before they have time to reproduce again. (BTW, I just used neem, which had failed me in the past when I was more loose about how often I sprayed). Also, to be safe, I sprayed all over (stems, tops and bottoms of leaves, and even the soil around the plant).
Not claiming that I have the best solution... but after a long struggle, this is what finally worked.
P.S. I don't think I'd do so much spraying very late into flower (2 weeks seems safe though). If late in flower, I'd just keep them at bay with iso alcohol + water (50/50), which evaporates quickly.