Answer: It is difficult to determine the exact reason for the leaf drop. Rhododendrons like a very well drained yet evenly moist (meaning not soggy) soil with a pH in the acid range of 4.5 to 5.5 being ideal. It is possible that a disease or insect is causing a problem; it is also possible that you are watering it too much. If you keep it mulched, and it has been raining, you may not need to water it -- stick your finger in the soil and see if it is moist or dry so you know for sure.
In any case, clean up and destroy the fallen leaves; this will help control the spread of any disease or insect problem.
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