Hi,welcome to GoY, are there any black blotches on the leaves anywhere, ?, it could be holly leaf blight, {phytophthora ilicis} a fungus type infection, causing black blotches on the leaves, and blackening on the smaller stems, best treatment is to cut off and burn any affected leaves or shoots, the infection usually occurs during cold wet conditions, but the spores can survive warmer, drier conditions, and become active again when conditions are right, Derek.

Hi Derek,

Thanks for responding. The leaves are fully brown, not spotted. The stems go black and brittle and the disease seems to spread along the hedge by about 1 foot per year.

Steve

Hi Steve, I think it probably is holly leaf blight, this is what causes dead looking patches in hedges, the leaves don't have to be completely black, but more often than not, if they're new plants, it is possible that they were infected when you bought them, I would contact your supplier, Derek.