in the intervening years.. have the arbs ended up in full shade ???

that might be one explanation for the thinning.. and overall decline ...

and once they decline ... lose vigor ... then other things might attack .. sooo ... solving the secondary problem.. might not return vigor ...

also ... if the shade trees happen to be highly aggressive super competitors .. like maple... they might not be getting the water they are used to ... especially if there has been severe drought.. in any of the last few years ...

it is not uncommon ... for a conifer ... to look bad after winter ... but its not necessarily winter that did it ... the insult or problem could have occurred anytime in the last year.. thats why i mention drought ... its a 'tree time' issue ... things just dont happen this fast with conifers ....

i dont do boxwood ... because of all the inherent issues with them ... sometimes its easier to divest.. rather than invest in working with a problem plant ... if it were me.. i would cut out all the dead stuff .. see what happens this year.. and if it lacks vigor.. be done with it in fall ...

in the alternative.. after cutting out all the dead .. if it was ugly as sin.. i might just do the removal now ... lifes too short to screw around with a boring old green plant that doesnt flower.. and needs to be sheared all the time.. you can do so much better.. imo ...

ken

Been no changes in surrounding shrubbery or trees. The boxwood patchy deaths have been a minor problem for years but we're seeing more of it. Pruning out the deadwood leaves a space that never gets filled in. The Thujas went through the winter very strongly until this began to happen in early March. I'll call VCE, and check an expensive Ortho Problem Solver book we acquired in better years.

My thujas look like that, too. They looked fine all winter and then Bam! Out of nowhere they started loosing a lot of their needles and fullness in early March, especially the ones that don't get as much sun. I have observed that many of my neighbors' look similar.

Ken might be right about the water conditions of the past year. We had a really dry summer and fall in upstate NY. I read somewhere that even after the blizzard we had a couple weeks ago that our water table is still lower than normal. Rey, has it been dry over the last year where you live as well?

The southeast had a drought last year. Virginia is currently on drought watch - northern VA is already four inches below average precipitation for 2017. I'm betting that the OP's problems are water related.

Central VA has had a mild drought, nothing severe. It hasn't bothered other species, and we have around a dozen different evergreens in multiple plantings. These are in a well-watered location. This is early to start watering but I'll try that. Appreciate the input.

Traded-in a nonfunctional head for a better one. Yes, these trees have competition they didn't have before. The Smaragds have been shaded by a peach that tripled in size in the last 5 years. I had the offending branches removed last month. Improvement is visible. The boxwoods are under a willow about 45' high and VERY loaded with small and large branches. It was damaged in a windstorm in 2010, lost the top 2' of trunk, and almost immediately began sprouting leaves and small branches everywhere. I don't trim willows because I like that look, but the shading of the boxwoods is greater than 90%. Thing is, the ones in the most shade are still green and lush. The death is shrub-specific.

Very dry here in Northern VA. I've seen a few of these dry up here. People don't think to keep them watered. But a closeup might help on those. Also, once weakened by drought, they can fall victim to other maladies.