Here is a link on leaf spot. Shrub type may be off.

Here is a link that might be useful: leaf spot

It looks like a Photina hedge.

Oftentimes there is nothing one really needs to do to eradicate leaf blotch. It is quite weather dependent. Why is the hedge thinning? Has the exposure changed over the years? From the looks of the photograph, it is in a quite shady area. As nearby trees grow and mature they can alter the exposure of underlying plants considerably and it happens insidiously since it's over the course of years. Use to run into that ALL the time with homeowners who wanted to plant shrubs or put large planters on either side of their home's entrances......but would have sun on one side and shade on the other. They never liked what I had to tell them.......IOW the flora in the sunny exposure would not look identical to the flora on the shady side.

It IS photina (Photinia fraseri) and it has photinia leaf spot. This is a fungal disease that while encouraged by climate, becomes systemic to the plant. It causes spotting, eventual leaf drop and over time the shrubs become so weakened by lack of adequate foliage they die off or are affected by other pests or diseases. This is a very widespread problem throughout much of the southeast and Texas and a real problem here in the PNW as well. It is not really recoverable, although spraying (and in some cases, hard pruning) can slow the downward progression to some extent.

My suggestion is to consider replacing the hedge. One seldom sees a robust photinia in this area and those that are in good health seem most often to be individual plantings, not hedges. Most of the better nurseries here no longer carry this plant......