The leaves of a normally healthy, mature Rhododendron of approximately 15 years, mysteriously went limp last October. This plant is a hardy seed grown variety which requires low maintenance. And now that the weather is warming up, the leaves are more limp than ever. I am knowledgeable regarding acidity, soil composition, planting depth and location but not so much regarding diseases. I've been online trying to search out the cause(s) to no avail. Is there anyone who might be able to offer an explanation. Puzzled J.
Maybe honey fungus, look near the base of the stem for telltale signs (search Armillaria on the web).
this is a good article http://www.rhododendron.org/v48n2p85.htm i, too, have lost many rhodos (I usually plant the 4 foot x 4 foot type in our relatively small garden at the coast)
It could be a Phytopthora infection in the roots. I have had rhodos suddenly fail in the way you describe.Within 6 months the whole plant died and it had to be removed. It is not recommended to plant any new Phytopthora susceptible plants in the same location.