Removal of old blooms prevents seed production and helps assure plentiful flowering the following spring. Insects don't cause trouble as often as do incorrect cultural practices. Rhododendrons are not commonly beset by harmful insects. The most common azalea pest is azalea lacebug, a small insect that sucks sap from the foliage leaving it bleached and silvery looking. Careful inspection of the undersides of the leaves will reveal the tiny adults and nymphs.
Plants are more susceptible to lacebug infestation when grown in full sun.
Follow all label directions carefully.