Answer: Based on your description I suspect it is a fungal problem, Entemosporium, which widely affects Photinia. New plants would likely become infected as well, so if you decide to replace these you might want to consider using a different plant. This can be difficult to control once it is widely established throughout the plant and if left untreated could kill it. Weather is a contributing factor, but good air circulation and keeping the foliage dry (for example when you water) can help, as can pruning to thin the plant to allow air to move through it. Cleaning up and disposing of any prunings and fallen foliage will also help limit sources of reinfection. Cutting it back very short would limit the area that needs to be sprayed, but would not cure it. Generally speaking, it will require routine spraying to control it with careful attention to contacting all of the plant from top to bottom and both sides of the foliage. I would strongly suggest you consult with your county extension for a specific diagnosis and based on knowing that, their recommendations on how to treat it. They will be able to tell you what to use and the best time(s) to apply it. I'm sorry about your shrubs.
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