Laurel hedge diseased / dying

Hi all, hoping someone might be able to help rescue our laurel hedge. We’d noticed more and more brown leaves appearing and upon closer inspection quite a few of the plants have a white residue on the bark. The branches that have a lot of it on them have already died. Some of the plants also have holes in their leaves and one whole bush has died. Does anyone know what it could be and if it’s treatable and, if so, how? I’ve tried a bit of googling and wonder if it’s white prunicola scale? We’re desperate to save it because without it we’ll have no privacy. Thanks for any help you can give me! :-)