I bought systemic Baer Advanced Tree & Shrub Insect Control to rid 3 30+ year-old Noble firs of aphids. It's easy to apply, and not so toxic that it requires an expert. I doused the soil around the trees' base last spring and repeated this fall although once a year is supposed to do it. (Fall is the best time to apply.) I won't know if it's effective until next spring. Sadly, the damaged lower branches will never look good again. Keep even well established trees watered during drought and they won't become so susceptible to pests.
I had some aphids and other bugs devouring the Andromeda leaves and this was a suggested solution. The instructions recommend a topical treatment directly to the leaves so I use malathion for that. I'm guessing the combo treatment could work, but I may be too late.