this is one of those things I can't believe I'm posting but I was told methylated spirit tickled on with the smallest brush you can find - I tried it - it worked. They went on to say something about watching the babies under the shell (I am hoping you'll get a better suggestion but hey)
Sudden infestation of scale insects on Makrut Lime - anyone got any good remedies?
(sticky sap all over was first sign)
Plant itself is pretty strong and a good 6-7 years old.