CULT: Crown Rot(s) and Southern Blight

From: <HIPSource@aol.com>

Bernard downunder wrote:

<< A couple of you are now suffering the joys of what is referred to in
Australia as Crown Rot.  It causes yellowing of the base of the crown fan and
into the rhizome.  It may be quite mushy (depending on the severity of the
infection) and might also smell of mustard.It occurs in bearded iris that are
grown in humid, warm conditions or which suffer an unusual burst of such
weather.>>

How curious. We have a crown rot here in the Southern US as well. Probably
several of them if the truth be known, but one in particular which is very
distinctive, very destructive and not specific to irises. What it can do to
columbines or hostas would make you weep and it just carried off my Clematis
montana. Our rot is called Southern Blight, or Mustard Seed Fungus. It is so-
called because, after the fine white webbing which forms across the soil and
and crown of the plant----the active fungus----begins to go quiescent, it
forms resting bodies that resemble mustard seeds. Little spherical things.
First they are blond, then they eventually turn darker brown and in this state
they can  inhabit the soil for years awaiting advantageous conditions. The
soil-borne pathogen involved is the fungus Sclerotium rolfsii and it enjoys
high humidity, poor dainage, and poor ventilation, but the activating factors
are heat and moisture. It can carry off either bearded or beardless irises and
is to be taken very seriously. The only fungicide I know that is effective on
the disease is Terraclor, applied as a drench. Bleach will kill it on a
rhizome lifted from the ground, but not one in situ. I wonder if this is the
same fungus found in the antipodes? 

I noticed that the April issue of the AIS Bulletin had an article on disease
control, but in this article whereas Subdue was recommended for Crown rot-
pathogen unspecified--on beardless irises, Terraclor was recommended for
Botrytis. I would reverse these prescriptions, myself, so I wondered if anyone
had any new information on this point.

Anner Whitehead, Virginia Zone 7
HIPSource@aol.com 


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