CULT: root diseases - rhizoctonia?

Neil's comments about root pathogens has gotten me thinking more about
roots & non-Erwinia root diseases here.  A subject I know absolutely
nothing about, other than there are different kinds, & they include
facultative and infectious attacks from fungi, bacteria, & those little
invisible things (viri etc).  In hunting the web for some background
info, I ran across this (I think this was on a tree site, or maybe
soybeans)
====
 Rhizoctonia root rot - Rhizoctonia can cause a root rot of
older plants. ... Plants may be stunted and
appear less vigorous than adjacent plants. When plants are removed from
the soil, the root system may be
poorly developed, lateral roots may be discolored or rotted and the stem
may have a brick red discoloration
beginning at the soil line and extending in either direction. If plants
are stressed by hot, dry conditions, severely
infected plants may die. If cool, wet conditions occur after plants are
infected with Rhizoctonia, a flush of
secondary roots above the diseased stem area may be evident.
======
I have seen this brick red coloration on most if not all of the 'slow
decline' cultivars here - the mother rhizome may become a shell, brick
red on the inside, or it may be intact and feel solid, with missing
(rotted before I looked) roots, or with bits of brick red, dead roots. 
My extremely droughty gravelly soil may be the last straw that pushes
plants over the edge.  

Anybody know much about what kinds of growing conditions (climate, soil,
organic matter, fertility, micronutrients, pH, etc) are likely to
aggravate root diseases other than Erwinia/soft rot in irises?  Will the
Clorox cure work on roots that are infected with fungus or is it
internal where surface treatment can't reach?  I'm not ready to start
flooding my garden with fungicide.  

Is this another one of those diseases where a healthy crop of fungi
eating nematodes and other soil predators would help?
-- 
Linda Mann east Tennessee USA zone 7/8
East Tennessee Iris Society <http://www.korrnet.org/etis>
American Iris Society web site <http://www.irises.org>
talk archives: <http://www.hort.net/lists/iris-talk/>
photos archives: <http://www.hort.net/lists/iris-photos/>
online R&I <http://www.irisregister.com>

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