To prune new growth always presents problems. Should you not stop new growth, the trunk will increase faster, but, the shape of the tree may be come bizarre after a time. I have long advocated fertilizing from May to October. I like to do it every week, but again the contradiction. Also the soil mix must be porous to allow the elements to get to the roots.
Some worthies say that fertilizer produces rampant soft growth that dies back over the winter.
I ve not seen that effect if a balanced fertilizer is used. If nothing works, don t call me. I m trying to figure out my own plagues. For larger bonsai, the Korean, Japanese, and older forms of English boxwood have proven to produce fine specimens. Their ruddy bark and good buttress formation set them apart.