Dying juniper bushes.
Is the black plastic solid material that would prevent water from getting into the soil. I cannot tell from the picture if it is solid. It should be a plastic mesh that allows oxygen and water to penetrate the soil. If it is solid plastic it should all be removed to allow oxygen to move in the soil. Make sure this bed is not overwatered by a sprinkler. Junipers are fairly drought hardy plants and may suffer if kept too wet. Also be sure that junipers are not exposed to salt used to melt ice in the winter. They can be sensitive to salt damage. At this point all you can do is trim out the dead, make sure the plastic under the mulch is a mesh, use a fertilizer in the next couple weeks that is meant for acid loving and only water during periods with extended dry conditions. There are some fungal problems that can hit junipers if kept too wet especially from overhead irrigation. If you need to water this bed try and get it done in early morning which allows it dry out during the day.