I am no expert on gardening and would really appreciate some advice. I have a escallonia hedge running along the side of my house. The side of the house that it runs along is north facing but most of the hedge benefits from a reasonable level of sun. I have noticed that the leaves are starting to turn yellow with black spots. It reminds me of an attack by greenfly? on roses but I have checked both the affected and unaffected leaves and cannot detect any prescence. Is this a normal withering that happens in Autummn or is it being attacked by something