I have 4 laurels (not sure of type) in my front yard. Three are healthy and happy. However, one has started dying from the center out. It is the closest the the sidewalk, but I have not used any salt or chemicals in that area. I have also not used any chemicals or fertilizers on the bushes. All have received the same amount of water, sun, etc. as they are all right there together. I have not noticed any bugs on them. Any idea what may be wrong with it and what I should do to keep it alive. They were planted 3 years ago, but were about 3' tall at the time of planting, so I have no idea what their true age is. They are now about 5' tall and I'd hate to lose one as it would really throw off the landscaping as they are right in front of the house.

Image link: