unknown killer of [lants
The dead cherry laurels and boxwoods seem to be clustered in the same general area, as best we can tell from the photos. We suspect that the area is getting too much rain run-off, standing water, or does not drain well. This causes root rot diseases and drowns plants that can't tolerate such wet conditions. Neither of these species are soggy-soil tolerant.
The boxwood do not have boxwood blight. They may be showing some winterburn. This publications diagnostic chart may be helpful for the boxwood: http://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/hgic/HGIC_Pubs/TreesandShrubs/...
The area for both of these varieties is relatively dry, although some of the yellowed boxwoods may be getting more. more importantly, the yellowed boxwoods are right next to some that are perfectly green. The cherry laurels are definitely in an area that is dryer but also has seemingly healthy plants, and parts of plants (one branch and not another on the same plant) in the same area...a couple of feet apart. Coul dthe cherry laurels have a disease or be infested, even though the dead branches are very distinct?
Cherry laurels are prone to several diseases and pest problems as well as winter damage. A scale infestation that is severe can result in branch dieback. Take a look at this article about some of the common problems and causes: https://marylandgrows.umd.edu/2019/01/07/qa-whats-wrong-with-my-cherry-laurel-shrubs/
You can prune out dead branches at any time. Cherry laurels are beginning to put out new growth now so if you do not see new foliage, prune out dead stems or replace the plants that don't recover.
The bronzing color of the boxwoods looks like winter damage but this coloration also could be the result of boxwood decline (https://extension.umd.edu/hgic/topics/boxwood-decline). There can be variations in winter injury based on the type of boxwood/genetics --some are more susceptible than others. You can do some light pruning at this time -- or just wait for new growth to emerge. We do not recommend any type of treatment.
Refer to this publication for further information on common problems with boxwoods and recommendations for good care practices.