British Columbia: Help with ceanothus with oystershell scale

I have a once healthy ceanothus hedge in Kitsilano with large sections dying off. On close inspection I found an infestation of scale. After a Google search, it looks a lot like oystershell scale (like hundreds of tiny cumin seeds stuck to the bark, some mildew as well). When I cut the stem, there is some discoloration within the wood. My questions: is the scale killing the hedge or is the hedge already dying from previous winter damage or bad culture (not enough sun/water/nutrients)? I've taken out the 3 worst plants but there is still a bit in the remaining 3. Help!