Dried up buds fail to open then turn hard and brown. They are covered lots of tiny black bristly growths, which are full of spores. The plant is healthy in all other respects.
Rhododendrons, azaleas and camellias.
A fungus spread by rhododendron leaf hopper.
Flowering will be limited as buds can remain for two years.
Remove all infected buds so that at least the fungus spores don't spread this way too. If damage is severe, control leaf hoppers with a systemic insecticide.