Answer: The disease attacking your red tip photinias is known as Entomosporium Leaf Spot. This disease also attacks Indian Hawthorn (Raphiolepis indica). It is a major reason why red tips are falling from favor in the south and are being planted less and less.
The disease is very difficult to control. Regular spraying with a fungicide (your county Extension office can recommend some product options) can help keep it in check, but nothing will eliminate it in the long run. Fallen, infected leaves should be raked and removed from the area to lessen the innoculum level of spores which can reinfect new leaves. Avoid wetting the foliage with sprinklers at this encourages the disease.
The disease seems to be most active in the cool, wet rainy days of spring, and almost inactive in the hot, dry days of summer. The spots you see now are the end results of infection this past spring. This is not to say that a good bit of summer rain or sprinkling could not encourage new infection.
The disease is much easier to prevent with sprays than it is to cure once the leaves are infected. So if you choose to fight it with fungicides, plan on making applications every 10 days from early March through April and again whenever a new flush of growth appears on the plants.
If you do not wish to take on an annual spray task, you might consider replacing your red tips with another species (just don't choose Indian hawthorne!).
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