On 28 Jan, 11:04, Jennifer Sparkes wrote:
Sounds as if it could be Scale Insect/Mealy Bug and Sooty Mould.
Any chance you could post a photo?

Sounds like it indeed. I hate them. I've used soapy water and a sponge
on one of our office plants, delicately removing them, using my nails
if necessary and rising each leaves afterwards. Looked great for a few
weeks but they're back. I'm wondering if they are in the soil (?).

On our acer, it worked well, using a tooth brush and spraying soapy
water. They all went, but this plant was outside. I think it's harder
in greenhouse/indoor.