Die back can be an issue with japanese Acers unfortunately, but have you repotted sometime in the last 2 or 3 years? If not, it might need more root room. As for the blobs of white, probably scale insect. The ones on the woody parts can be wiped off firmly with a cloth just slightly moistened in meths, but if they're on the leaves, meths cannot be used there. Unusual though, because the scale that frequently infests Acers usually sticks to the woody parts only, not the leaves, so adding a photo to your question would make for a more definite id of the problem.

Prunus, not acer, Bamboo, ninny! Kojo-no-mai is a tough little plant, but this year they've suffered. To me it looks like fireblight, but whatever the cause it's devastating. Cut off the dead bits as much as you as you dare, and hope. It may be the end of it, sorry

I thought swcale insects too - try painting some of them with meths and see if it makes any difference.

Oh dear, sorry Mrswithers, mistook it for Acer, as worthy rather rudely points out, tut tut, no need for name calling Worthy, we ain't in the infants playground, are we, anyone can slip up from time to time, and I am certainly not exempt from that. Not sure it makes me a 'ninny' though...and I never think someone else is for making a slip, but there you go, we're all different.

Still sounds like scale to me, but the treatment will be different than that I described. Check the root room in the pot...

Thanks everyone. Meths applied, breath held :)