It's the urine in the stable manure that cause's problems.
I read this in a rhodo book some forty yrs ago.
It also recommended cow manure diluted to the consistency of weak tea!.
I kept stabled horses for many years, but never was tempted to use the
the Manure on my azaleas etc…
If you think stable manure is suitable for your Rhodos, well give it a
try.
John