In article ,
Chris Boulby wrote:

Peter, this sounds very much like scale insect (not sure if that's their
proper name)to me. They are tiny creatures that are hard to spot
because they are flat and look like flaky bits. It happened to my
grapefruit tree a few years ago. Take a magnifying glass to the
undersides of the leaves at the main vein that runs beneath the leaf.
If you see brown flat bits there, you may have scale. I found it almost
impossible to eradicate them, and finally had to dump the tree
altogether, and I'd grown it from seed. It was 10 years old.

Yes. That's their name, all right, and there are several that can
infest bay. I have got rid of them from bay and citrus on SMALL
plants, by scraping off or damaging every scale with a blunt knife
or similar. 2-3 goes and they have gone. But that does mean going
over EVERY stem and EVERY leaf, which could be time consuming on a
larger plant ....


Regards,
Nick Maclaren.