Where are you? Generally speaking.

Remove the yellow foliage. Next thing is to go in and remove all of the old foliage in side, it win't have green growing tips or will be pointed down (dangling). Once it is cleaned and opened up it will help. Next, only prune to lignified wood, brown not green. Finally check with locals to see about fungicide requirements, or tell us where you are, and wstch outfor pedts like mites and bugs that feed on shoot tips.

Check for spider mites. I use neem oil according to directions with a touch of dish soap and a capful of alcohol in the spray bottle.

Could be scale too, my small Itoigawa is just getting over a bad infestation.  Same yellowing.

Scale could be the problem but spider mites generally cause the tree to turn greyish in color.  Put  a piece of white paper under the branches and with the flat of you hand kind of spank the foliage pads.  Look at the paper with a magnifying glass.  Do you see some dust?  Look at that with the magnifying glass; does it move?  If it does you have spider mites. 

Personally I think you are having a watering problem.  Your soil is not operating correctly.  The tree is either drying out and staying that way too long or it is sitting in soggy soil.  The results are the same both ways.