Stockport, Cheshire,
United Kingdom 
We have a 3year old Photinia (Red Robin) in a very large pot which has been very happy until this year. All its red leaves became marked with large black spots and then fell off. This season's new red leaves started to grow just red but now are badly marked with black and some have withered up. Went to a local Garden Centre clutching a leaf to ask the question why? and what do we do? only to find some of their Photinias were exactly the same and their 'expert' had no answers. There are gardens in the area with both healthy Photinias and marked ones like ours. Any ideas or suggestions please?
7 Apr, 2014
Answers
Thank you so much. Our plant has actually been in a windy spot (and we live in a windy area) all Winter. We will try moving it, pruning and feeding it and see what happens. Thank you for your help.
9 Apr, 2014
Previous question
It's most likely Photinia leaf spot - the RHS has a page on it if you want more info. There isn't a treatment really, but pruning back and feeding well are things you can do. Leafspot can be a sign of a plant under stress (could yours have outgrown its pot, be rootbound?) but is always worse after wet, windy winters.
If, though, they were more like purple blotches, then it could be powdery mildew, for which you can spray.
7 Apr, 2014