standard hydrangea suddently dying

Hi have this cherished standard hydrangea with a stem like 2inch thick. I always wait for spring to cut the dead flowers and shop it into shape.
I did this in early April then all the leaves started growing as usual but slow then slowed more and like went dormant then now in the last days all the leaves are shrivelling up and its like dead or dying :-(((
All other things around are growing as usual some even stronger like the azalea in front
etc..Its south facing nearly 2.50 m tall .. and age is around 7 years
It would be very difficult and disturbing to dig it out as I use for clematis to flower in earlier in the season
Thanks for any advise?

 

Sorry about your hydrangea's condition. To not know the cause makes its illness even more disturbing.
Assume that its roots have not been recently disturbed...?
Reaction to excessive heat/sun? Unlikely, as you say azalea etc unaffected.

Maybe this---?
Hydrangea limbs suddenly wilt and die | Walter Reeves: The Georgia Gardener.

Or this?
sudden death for hydrangea #411727 - Ask Extension

Fingers crossed that someone can help you correctly diagnose the problem, and that you can intervene in time to save your plant.

 

Hello thank you so much. Ha I wonder is it because I like to eat Okanagan Ambrosia apples and sometimes I toss away the kernel for the birds to eat. Ok I just gave it the advised hair cut I hope this was a saviour type of operation. Anyways otherwise it will only become a stake to hold some clematis. Is there anything I could spray? I have this spray against black sport on roses ..but even this year with rains no hope most leaves are getting these spots even I sprayed before.
The wood stems seem OK and sort of still fresh with a brighter heart of the stem. I don't know if the small dots on the stems are normal or not. Never looked at them that close. There are a few holes. But they have been there for years when previous stems were trimmed . NOTHING was disturbed around this plants for years but three years ago I tried my luck with a stem of purple lilac that actually has taken and is now peeking through the azalea that has grown VERY strong this year. It was much more thin and less leaves the year before. It's a peach yellow colour everything around is grown as normal. And YES we had eight month of very wet weather than one day 30C but I had watered before in the morning. Thank you very much

 

Hmm. All that rain might have encouraged fungal root rot... ?
If so, why it would affect ONLY the hydrangea and not your other plants---??
Yet another botanical mystery.

Here is a 'home remedy' I have read about. Have NOT tried this so cannot say if it works, but perhaps it might be worth a try.
Mix one part 3% percent hydrogen peroxide with two parts water and carefully pour it over the plant’s root system with a watering can or spray bottle.

This will kill off the bacteria which causes root rot.
Above from:
How To Use Hydrogen Peroxide For Root Rot?.

 

THANK YOU I will try we are having a heat wave now