I've given 3 doses of pest-oil to scale on a finger-lime over the past few weeks. There was no change, possibly a slight reduction. Many of them were black, and I guess all the little ants would have helped spread them each time. So I reckon you've gone the right route with picking them off.
After reading this I went and tried to pick them all off my lime. I was trying to help the tree, but it just kept stabbing me anyway
p.s. thanks for adding this in dog, I hadnt heard it before and it's good to know
bonzaidog wrote:...but make sure that you eradicate any ants in the immediate area as they look after the scale from predators and farm honeydew from them...