HI NEIL
I think you got
Latin name Eriosoma lanigerum
Common name Woolly aphid also known as American blight
Main symptoms Lumpy swellings on the bark and, in summer, colonies of aphids covered in white fluff on the trunk and branches
Woolly Aphid Control
Since severe woolly aphid attacks rarely occur, there is little need for woolly aphid pesticide for control. Generally, their numbers are kept low with natural predators like lacewings, ladybugs, hover flies, and parasitic wasps. If desired, you can spot treat where the aphids are most abundant using insecticidal soap or neem oil. You can also prune out and destroy infested branches when feasible. When chemical control is deemed necessary, woolly aphid insecticide such as acephate (Orthene) can be used to control these pests.
kevin