Pam, I am not a tree or shrub doctor but black sounds like some sort of fungus. I suggest you take a sample to your local garden center or nursery that specializes in shrubs. Too much water could be an issue. I know of few places that have moist sandy soil this summer unless the area was well irrigated. But lots of folks overwatered their plants this year. Let them know how old the shrubs are what is going on with other plants in the area. Also arbs need a minimum of 4 hours of sunlight a day. Are they getting it? Best And Happy Yardening, Nancy.