Laurel Bushes Disease

I have a mature laurel hedge bordering a lawn. A few weeks ago I used lawn sand to kill off moss on the lawn's edge next to the laurel bushes. The moss has disappeared and the lawn is growing well but the laurel bush is withering. About half of the leaves are curling up with a white powder on them.
I can olnly think it is the lawn sand which is the cause and so I have dug in plant feed and new topsoil to help replenish the soil nutrients.

Any suggestions what the problem is and possible solutions?

thanks

MM