We Have a well established large Rhododendron in our yard that started dropped a substantial amount of leaves about a year ago & earlier this spring it started dying off at one end & is progressively getting worse. (Our next door neighbor also has one that is dying.) I imagine its a fungus or disease of some kind. PLEASE let us know what's wrong & what we can do to help this beautiful shrub!
Many woody ornamentals have been affected by the abnormal rainfall we had last year and this spring. If soils are saturated, there is no oxygen in the soil which affects the root system and can lead to branch dieback and decline. We also had a drought that affects the root system too.
All you can do is prune out the dead areas and see what comes back next spring. Check the drainage in the area and improve if necessary. Water the plants during dry periods and make sure mulch is no thicker than several inches and away from the base of the stems. No chemical controls are recommended.