Aphids (which come in different colours besides green). The other black is sooty mould growing on their droppings.
So deal with the aphids by whatever means you think fit, from a hosepipe to insecticide. Then treat the mould with a fungicide of some kind. (9 parts water to 1 part full cream milk is supposed to be a good organic one).

The milk treatment only works for powdery mildew, Owdboggy - otherwise, agree - spray with an insecticide, including under the leaves, to get rid of the aphids (preferably a systemic insecticide rather than a contact one) if that's what they are - they may actually be scale insect nymphs, so check the woody stems for adult scale insects too. If its scale insect, you need an insecticide that works on those rather than just aphids.

The sooty mould should just disappear on its own, it doesn't harm the plant in and of itself, its only there because of the honeydew from the aphids/scale, but you can gently wash it off with a cloth and some water if you like. It will probably wash off in the rain after you've disposed of the infestation.

Well there you go. Since I never spray anything with anything, how would I know? Thought milk was a good fungicide for almost all fungal infections. Wonder if it works on Athletes Foot?

Doubt it! Good old fashioned Whitfields ointment is brilliant for that, much better than all these modern fungicidal creams.

Never heard of that Bamboo - will make a note! The new ones aren't a patch on the old ones.

Not all chemists stock it, Steragram, its rarely prescribed any more, but you can actually just buy it over the counter, if its there. Got rid of my son's Athlete's foot years ago, after he'd been prescribed several different more modern treatments - my old GP, I recall, sighed when we went back for the umpteenth time, and said 'oh well, back to the old days' (Ive never forgotten her saying that) and gave us the ointment instead.

That said, I'm sure Owdboggy was just joking, didn't actually want a cure for athletes foot;-))

Possibly not but I do, in summer I've only got to get a bit of soil between my toes and its away...

Ah well, get yourself some Whitfields then, keeps for a year or more I seem to recall. You'll have to ask at the pharmacy counter, won't be on display.