What's killing my boxwood shrub?

I'm not much of a gardener and don't spend a lot of time in the yard other than mowing the lawn and pulling the occasional weed. So I'm an idiot when it comes to gardening. I noticed today that one of my boxwood shrubs has pretty much died, all but one little area. I thought at first it might have been from a dry summer and a couple of recent freezes. But on closer inspection, I can see the that leaves are covered in little white lines and that it seems to have spread to the shrub next to it. I thought at first they were worms or insects, but they don't move. Then thought it might be some kind of fungus.
I'm not sure what it is or what to do about it. So I could us some help and direction.
I've attached a few photographs of what the leaves look like.

Thanks,

Erik

The plant in question is Euonymus, and the pest is Euonymus Scale.
Scale is a group of insects with an interesting life style.
Mom lays eggs, and protects them.
Babies (called Crawlers) crawl out from under Mom, and move to a nearby part of the plant and start sucking the juice.
When they mature (timing varies among the species and weather) they settle down on the leaves (in this case) twigs, or bark of the plant. They mate, the males die, and the females live over the winter to lay more eggs. In the case of the Euonymus Scale, there are 2 generations per year.

Scale are hard to kill because they are protected by a waxy covering that resists pretty much all pesticides. I think I would give up on the plant that is so badly infested. Remove it. The bush that is just starting to get it can be treated. Some scale can be killed by smothering them in a particular type of oil sold for plant, called Volck oil. Systemic pesticides make the plant poisonous to the scale. They suck the juice and get poisoned.

http://ento.psu.edu/extension/factsheets/euonymus-scale

Wow.. That's it. Makes my skin crawl.
Thanks for the identification.
I'll rip out the dead one and see if I can treat the second.
Thanks again.

Erik

There is a devestaing Disease here in UK where most Box hedges this year have been attacked by Box scale or Box mite, as Diana has pointed out, it is nasty, Most people think the plants are in need of water when they see the foliage drying up and looking withered / dead, If you get sight of this early on, you can prune out the damaged parts, burn the stuff you cut away and wash the tools afterwards before you spread the disease or mites, I think the plant you mention is dead should be removed right away, prune the plant next to it that you say is being attacked, watch over the next few weeks and see IF the decay is stopped, if not, then do as recommended and either spray, or wash, I use vinegar or Surgical spirits bought from pharmacist, dilute it with water, and start by spraying the undersides of the leaves, you may have to repeat this treatment several times a few days apart. OR fill a bowl with the mix, use an old sponge and holding the branch in one hand, run the sponge up the undersides of the plants in question, this should make the insects loosen their grip on the foliage.
Don't be worried about being bitten or harmed by these tiny sucking insects, they dont live or like humans.
Pour the remaining mixture around the base of the plant to help prevent any more arrivals.
Good luck, hope this helps you out.
Kind Regards,
WeeNel.

Don't wait to spray.
Optimum time to spray scale insects is when they are in the crawler stage. For Euonymus scale this will be twice a year (see that link). But spraying them any time will start to kill them. It is especially good to spray in the cooler weather because you can use a horticultural oil (such as Volck Oil) to smother them, and not harm the plant.

I don't know about Euonymus scale, but I've successfully treated Sago palms for scale. Remove the affected fronds, bag them, and discard them. Thoroughly spray (soak) the remaining fronds, trunk, and soil at the base of the palm with all-seasons oil (which apparently suffocates the scale insects). You can buy the oil in a container that attaches to the end of a garden hose. Repeat the spraying two weeks later.

Depending on how many boxwoods you have, how large they are, and how badly affected they are, you might want to decide between treating and removing and replacing. Whichever you do, treat with the oil early on during any subsequent infestations. The sooner you take care of it the better.

Yes, removing the heaviest infested leaves and treating the rest works.
Note that the plant in this thread is Euonymus, not Buxus.
Euonymus grows pretty fast, so the choice to either prune heavily or totally remove a badly infested plant is not a problem.
Treating with any sort of oil can be done year round, as long as you watch out for a few things.
I know these apply to Volck oil, probably to other oils:
Do not spray when the temperature is too high. This may vary with the species. Do some research.
Do not combine with sulfer sprays.
Plants that go dormnant (not Euonymus) can be sprayed with a stronger concentration than a plant with leaves.
You MIGHT be able to use a slightly stronger dose in the cool weather, even if the plant does have leaves.
Research the pest to determine the optimum time to spray. When the pest is most vulnerable is important (scale is most vulnerable in the crawler stage).
Look into alternative oils, such as vegetable based oil sprays. Many years ago KXL was available, but I think it is not any more. (Not sure why).