I was visiting a nursery two day ago and brought in a picture and leaves from a boxwood (English) that in November had signs of leaf minor. At that time I used a drench of Merritt. The staf person examined the leaves and said the leaf minors are no longer a problem, but I should treat the plant with daconil to deal with boxwood decline. I did not see boxwood mentioned on the label and in reading an article from the South Carolina Extension Service, I did not see any chemical treatments recommended for boxwood decline. Maybe, daconil should not be used on boxwood?
Montgomery County Maryland
This does not look like boxwood leafminer. This looks like a type of winter damage, vole damage, or a type of physical damage. Check around the base for possible vole damage http://extension.umd.edu/hgic/voles, gnawing around the base of the stem, holes in soil, etc.
Boxwood decline is a term used for poor growth that is caused by a combination of factors such as drought, poor soils, deep planting, etc. as well as insect and disease issues. No disease issues were mentioned. Daconil is a fungicide that manages some disease issues. We recommend pruning for control.
All you can do is prune out damaged foliage and this is half the plant.
Here is our publication on boxwood http://extension.umd.edu/sites/extension.umd.edu/files/_images/programs/hgic/Publications/HG52_IPM_B...
If I prune the dead branches from this boxwood, as you suggested, will the plant, dwarf English, ever grow more branches?
If the shrub is otherwise healthy, yes, it should send out new growth in the spring.