If forceful water spray doesn't remove them, get some spinosad (Captain Jack's Bug Brew). It is approved for organic gardening. There are also house brands these days. Spray in the morning or evening when the bees aren't doing their thing.

Every year it is something...it seems. Last year I had gobs of sap dripping off my maples and this year nothing, I think because of the weird spring rains up here near San Jose.

-Babka

The aphids love a huge Hawaiian umbrella tree that I have. I just set the hose to "Jet" and spray the heck out of them. Gone. Whenever I see them coming back, the Jet returns and they're toast.

Aphid predator populations, and predator populations in general always lag behind their prey, because that way, the predators won't starve. Keep hosing off and wait. The predators will soon arrive and take care of them for you.

Forgot to say that there is a thingy that you can put on the end of a hose called a "bug blaster: I produces a very fine but forceful spray of water that I have successfully used on tender Japanese maple new leaves, as well as on camellias.

You need to go out every day for several days to do it, but it washes those critters right off the miost tender leaves, that a regular nozzle might damage.

-Babka

Here is a link that might be useful: Bug Blaster (it really works)