Can anyone help me ID this pest & recommend suitable treatment.

I have tried to use google, but have not been able to find anything.

This is really a crude description; the pest looks line those
barnacles you get on rocks at the beach.

They are only 2-3 mm diameter and 1-2mm high, shaped like a shell and
are 'suckered' onto the leaves of my Golden Cane palms. They are
coloured grey, with a rough textured look on the outside. There are
hundreds of them throughout the clump.

Thanks for any help in identifying this pest.