You may consider such products from our sponsor, Sierra Natural Science. Products such as SNS-217 or SNS-203 would help to kill/fend them off. Other options would be a product called Azamax.
I have dealt with Scales before, their initial white egg case releases hundreds of eggs and they suck the juices out of the plants. Since they have an armored shell, you may want to consider Azamax, or just manually removing them by hand (though tedious).
They can be a real nuisance because their egg cases release so many larvae, and potentially could kill a plant during their feeding stage.