I am raising lots of milkweeds this year and they were a aphid magnet. I tried washing them off but was flooding the area with water and aphids returned each day. Since I am trying to attract bees, butterflies, etc., I do not use chemicals and finally decided to buy some ladybugs. I have done this in the past without success but followed the instructions to the letter. Keep them in frig until release. Just before dark, wet the leaves on plants. Release the ladybugs - they will be looking for water. The next morning there were still lots of ladybugs but with time, many "took off." Enough stayed to take care of my problem and still see some occasionally.

Have you tried to spray them with water with a few drops of dish soap? It has worked well for me, it also kills the ants that bring the aphids. Any hand sprayer will do the job.