I would add to the "in favor of bleach" comments.
I have had spectacular results on rhizomes by using bleach. I was
rarely able to save a rhizome with rot before I started using bleach.
Since I started, it has saved many of them (if anything viable is left alive,
they usually recover now). I discovered bleach in desperation when looking
for a cure for fungus diseases in Cacti. I found that I could clean the
rot out, soak the Cacti, and they often recovered fully with no re-appearance of
the fungus. Results were not so good with bacteria in Cacti, but then once
a bacterial infection is noticed in a Cactus, the plant is usually already
infected from top to bottom and for a practical purposes it is already
dead. Even so, I've even saved a few with bacterial infections. So,
I tried it on Iris. It worked. The liquid bleach that comes out of a
bottle from the store is not very strong, and I've never had any damage on Iris
from the bleach, even when I cleaned the rhizomes in situ and pored the bleach
directly over the plant. It does kill everything else around the Iris, and
all the critters that are eating the rotten flesh (pill-bugs, maggots, beetles,
snails, slugs, whatever. This (I feel) is good too, as these critters seem
to be vectors of the rot organisms.
I have noticed that if too much bleach is in the soil, the plant does not
regenerate as fast as if I use powdered detergents, but those are not quite as
affective at sterilizing the infection and sometimes miss some pockets of rot
which the liquid usually soaks into. I suspect that the high concentration
of bleach inhibits root growth, but it seems to cause no permanent damage, and
once the plants do start to grow, there are no ill-affects.
I should add that (after reading other Iris grower's comments) I've
tried several powdered detergents with bleach included, and they do tend to work
nicely. I've actually taken to lightly dusting certain rhizomes with them
before I plant them (particularly making sure it gets down into the fans.
I get much less rot in batches so treated, than not treated. It does work
well as a preventative on fresh cuts with no apparent damage. I'm not sure
if the type of chemical in the "bleach" is important, but it seems it is usually
a chlorine compound. Things like "Comet" and "Ajax" work nicely.
Seems to me that even though these multitude of accolades for bleach are
not based on controlled studies, it is a pretty good recommendation for bleach,
and pretty strong evidence that it does work.
Regardless, I still have occasional rot problems during hot weather,
especially in young plantings, but I haven't yet taken to preventative
treatments of established apparently healthy clumps (yet).