In the views of the plant bases there are a lot of stems close together. And some crossing ones. However this is a hedge planting, and not a row of separated specimens intended to stand out from one another visually, have specimen tree style structure with attractively organized branching.

And if you are seeing a spotting that appears to be causing premature dropping, a resulting thin appearance cutting out sections to force production of new stems from lower down may actually result in a worsening of the problem. Due to new sprouts from cut stumps also being susceptible to infestation.

This is what I had happen some years ago with an infested plant on Camano Island anyway. The kind of spotting (there is more than one) we have in my area is making these plants go bald, yours do not look nearly as badly afflicted. In fact a 'Birmingham' at the Seattle arboretum that was 26 ft. tall in 1994* was almost entirely bare when I walked near it recently, there being only a small number of dwarfed looking tufts of new leaves present.

*Other Fraser photinia elsewhere in Seattle were over 34 ft. tall by 2005. And were still growing. Now, of course, most here have become gaunt and spotty. Or will do soon

I wanted to prune to thin, not to force new production. So you’re saying I should let it be? I’m afraid if I do, the lack of airflow will make what I think is potentially fungus worse..

I do realize that pruning will potential revitalize the bushes into new production, I suppose I could keep cutting out this new production as I do like the look of the barer trunks.

Mine do have some areas that are bare, in the center of one is pretty much bare and one down low has a spot that has completely dropped it’s leaves.

On the pictures I was trying to show the scaley trunks vs. the smooth trunks. And also how crowded the bases are. Each of the 8 bushes are this crowded at the base. Each bush is at least 20 ft tall with only 4 feet between each bush at its base. They were planted originally far too close together. Maybe if they were kept pruned and smaller the plant spacing would have been fine, but these things are huge!

Maybe I don’t know what I’m talking about tho! Ive never had a massive Photinia hedge before :)

If the intention here is in fact a hedge or screen then density and solidity would normally be the main objectives. With the individual landscape element being the entire hedge, rather than each plant - each plant is a part of a whole, rather than a separate feature unto itself (specimen plant).

If the height has become more than you want then go through and lower it at a uniform level, with spring being the preferred time to do this. Keeping in mind that if this is done the planting will then go about trying to restore its original size, have to be lowered again at some point in the future.