The following was received via email: One of my rhodos has quite a few buds which turned black after growing to approx. one inch in length. These buds are dry and dead inside while other buds beside them matured normally and bloomed. Under a magnifying glass the surface of the dead buds is a forest of tiny round-headed toadstools. Is this a common affliction for rhodos? We have several and have not experienced it in the past. This plant is about 15 years old, 7 to 8 ft high, appears otherwise healthy.
I think this thread answers the question (see "bud blast" and the response about fungi blackening the dead buds).