cliff_the_gardener wrote:

With the caviat of not having seen the problem.
I am not familliar with mealy plum aphid.
Having checked Stefan Buczacki's Pest, Diseases & Disorders of garden
plants - he does list it. He states that the leaves are not deformed
by this pest, they exude a lot of honeydew resulting in sooty moulds
(as leaf curl aphid does later in the season) and that it does not
build up to damaging levels until mid summer.

Thank you for going to the trouble of looking it up, and apologies for
not replying earlier - there's always so much to do outside!

If the leaves are curled then I would suggest it is plum leaf curl
aphid.

It may well be, but happily it doesn't seem to have got much worse.
It's not affecting every leaf by any means, and even the worst leaves
don't seem to have more than a few dozen aphids. When I first saw them
I expected they would quickly multiply and become a serious problem.

In fact since about May I haven't been much troubled by aphids on
anything this year. I'm not sure whether it's the weather, the
ladybirds or my ministrations, but I'm hard pressed to find any blackfly
on my runner beans at all now, so I've mostly stopped bothering to
squish them. Plenty of ladybirds (adults and larvae) last time I
looked.

Peter