Boy.. it sure might help.. if you had provided a picture from worser days ...

is there a spigot back there.. are you drowning the things...

what if any impact might the air conditioner have on it.. now that it is much bigger ... reflective sun from the siding.. plus the heat from the air conditioner might have a bigger impact on a large specimen.. than it had on it.. when it was smaller ...

whats on this side of the retaining wall ... do you spray chemicals/weed killers on your lawn? or if its a sidewalk .. do you use chemicals for ice removal ...

do you fertilize it ....

so many questions.. so little time.. lol

ken

Ken,
the only thing I can think of is I had a Rainbird sprinkler system installed this summer along with EZ flow fertilizer system.
It injects minute amount of fertilizer when it waters, supposedly below the level allowed in drinking water.

Anyway, my other Diablo is watered by the sprinkler system and its not affected by it, nor are my other shrubs.

As far as the wall is concerned, one thing comes to mind. There was sand/gravel used as backfill when the wall was built. It could be that some roots are reaching the sand/gravel at this point. Not sure if this would pose a problem?

Also, no the spigot is not leaking.

thanks,
jasper

According to many other posts this year and last, your Diablo is extremely acceptable to some kind of fungal disease.
Many posters here were complaining about the same thing you are.
Do a search on Diablo Ninebark on this Forum and read the posts.
Sorry.

I am noticing on my 3 year old ninebark that a white fungus is spreading on the leaves and causing the branches to dry up. Is this the same fungus which grows on roses? I had some rose bushes planted in the same spot before the ninebark. Could I try the same rose fungus powder on the ninebark?

Root Rot. I've been growing Ninebarks for years which great success and then this also happened to me - suddenly the plants died. I'm positive it's linked to the mulch I used. I have 2 Diablos flanked by 3 Amber Jubilee's, and then a separate complimentary Diablo opposite of the garden bed. The complimentary Diablo and 1 of the 2 Diablo's are dying... nothing on the Amber Jubilees or the additional Diablo - which I planted at a different time than the other 2. The mulch I used was the Lowes dark brown brand - probably circa 2014 (plants died in 2016). I only used the Lowes mulch initially because I didn't like it much, switching to the Scotts Dark Brown - which I use everywhere now and have no other problems. The only plant and shrubs that exhibit decay are the ones I plant with the Lowes mulch.

Around one of the diseased Diablos I also have the mushrooms that are indiciative of Armillaria Root Rot - 1st time ever.