What you see is harmless lichen growing on your shrub. What I see here is a heavy growth of lichen which indicates that a more serious problem is at hand. The cause might be below ground attacking the roots of your shrubs causing slower growth and death. In a healthy plant lichen cannot attach so heavily because healthy plants constantly shed bark. This is somewhat similar to the way we shed skin cells. So what is in the picture is not a cause but a sign. As to what is the actual problem other members can perhaps tell you how to find out.

can you say what plant it is growing on as that might help. it is lichen and as loosestrife says it is harmless really. it is a sign of clean air.

Never heard of lichen killing anything.What other shrubs are affected? Were they healthy last year?