Leaf Spot Diseases
Leaf spot diseases caused by fungi like Alternaria and Phyllosticta are most problematic on pieris when conditions are humid or moist and plants are weak and crowded or poorly spaced. Leaf spots caused by Phyllosticta are tan or brown with dark edges. The center of the spot may dry up and drop out. Alternaria leaf spots usually begin as small, dark circles that may enlarge to have a diameter of over 1/2 inch, are gray, tan or black and may feature concentric rings.
Leaf spots are controlled or prevented by pruning out and destroying infected portions, selectively removing branches on the pieris and nearby vegetation to improve circulation, raking up fallen leaves, avoiding the use of overhead irrigation and, if necessary, applying a fungicide. Vigorous new growth produced following too-vigorous pruning or excessive nitrogen-fertilizer application is particularly susceptible to fungal infection.
@BoPeep75 I have copied and pasted the above information, and hope it answers your query.