I also have some rhododenrons in my yard. If left unattended, they grow from
a bush into a giant bush, and the leaves become so large they are no longer
attractive. Also seems susceptible to powder moss (?). For maintenance, I
was told to pick off the flower every year after they blossomed. That is a
tedious operation.

Deadheading is 80% or more just for tidiness. It won't hurt the rhodies if
you fail to do it, or do it only moderately on the parts that face the
garden & show most. Some rhodies to their dead flowers a long time &
produce seeds, but it doesn't seem to deplete their energy for the
following year's blooms. Some such as PJMs & many other Mezzit hybrids
drop their spent flowers on their own if you ignore them. Deciding to
pinch off the dead flowers from mature shrubs is a personal choice based
on how you think those dead flowers look vs how much of a bother it would
be to clean the shrubs up. Sometimes, as for quite young deciduous
azaleas, deadheading is simultaneously a chance for end-pruning that'll
cause the twigs to branch. But the same shrub un-deadheaded drops the
petals & retains only a spidery skeleton of the truss, which can be kind
of decorative if not removed, though I will remove them a few at a time as
mood strikes, no need to hurry. For the most part it's done for looks
since the shrub won't suffer if you don't bother, & it won't rebloom if
you do bother.

By "powder moss" do you mean powdery mildew? I've one azalea the lower
leaves of which get a mildew near autumn, but it takes care of itself
because it's deciduous & drops its leaves, & the problem has never gone
above the very bottom branches & has never spread to evergreen rhodies. A
spotty so-called powdery mildew that can attack evergreen rhodies is not
noticeably powdery like the stuff on deciduous azaleas or on bee balm.
I've never had to deal with the spotty kind on my rhodies but it's common
enough someday I'm bound to have to deal with it. The rhody guides mainly
recommend fungicides. But here's something you might try that is organic:
If you've seen the problem on specific shrubs but not others, you might
"treat" the problem shrubs before the mildew appears on newer leaves, with
a once-weekly spray of powdered skim milk diluted to a fourth of drinking
strength; be sure also to get underneath the leaves. Since I've been lucky
& never had to try this on evergreen rhodies I can't swear it'll work, but
it worked on honeysuckles.

If very few leaves are affected you could pinch those off & discard (not
compost). If the plant is otherwise healthy, it can usually survive & not
look bad since for many hybrids the majority of the spotting will be
hidden on the underside of leaves. The evergreens drop their leaves in
two-year cycles, & these should be cleaned up & discarded in the trash.
The problem should be manageable without recourse to fungicides, but I
realize that's easiest for someone to say who hasn't had a problem with
it. Any shrub that seems especially prone to the fungus could be dug up &
banished to a part of the garden where it is nowhere near other rhodies
(or replaced with something that has no R. cinnabarinum in its hybrid
history, as they're said to be most susceptible), & look instead for
rhodies with R. yakushimanum or R. augustinii in their hybrid history. Our
local native Northwest species of rhodies are also impervious to the
mildew. A few hybrids such as Vulcan's will let the mildew badly mar the
top surface of the leaves, but a great number of hybrids are capable of
keeping the mildew to the underside of leaves so that infected shrubs are
not bad looking. Here's a widely circulated tip sheet:
http://www.rhododendron.org/v53n2p73.htm

I've tried to guess what I may have done that keeps the problem out of my
gardens, & of course it could be nothing but "lucky so far." Still, I
think my methods do have something to do with it. Rhodies are more
susceptible if planted too many too close together in overly shady areas,
so don't crowd them, make sure they get SOME sun, & break up the shrub
array with unrelated shrubs such as Fothergilla or Ninebark or Kerria or
dwarf Yew, or whatever. Rhodies "isolated" between unrelated shrubs are
less susceptible. They're more susceptible if they are too warm through
winter, so should not be planted up close to walls of the house especially
if the house is poorly insulated & warms the shrubs all winter (the stuff
I put closest to the house is stuff like winter jasmine or blue potato
vine or tasmanian giant fern that benefit from the residual warmth through
the winter). Water under rhodies with soakers rather than sprinklers so as
to keep humidity down, but at the same time don't let the ground dry out
too much in summer since stressed rhodies are more susceptible. Shrubs
that are too compact or hemmed in by other shrubs need to be provided
better air circulation. I used to be 90% organic, but now I'm 99.99%
organic, & when I see other gardeners who use lots of chemicals also
getting lots of diseases that require lots more chemicals, I increasingly
believe that the more chemical assistance given to a garden, the more
chemical assistance will be required; & the less chemicals are used, the
better the overall balance in the garden so that chemical interventions
become less & less called for.

Here's a link to that one azalea I have that does get mildew on its lower
limbs very briefly toward the end of autumn:
http://www.paghat.com/azalea_whitethroat.html
Here are its autumn leaves, for which you would never suspect any pathogen
at all:
http://www.paghat.com/autumnleaves7.html

-paghat the ratgirl

--
"Of what are you afraid, my child?" inquired the kindly teacher.
"Oh, sir! The flowers, they are wild," replied the timid creature.
-from Peter Newell's "Wild Flowers"
See the Garden of Paghat the Ratgirl: http://www.paghat.com/