From: jwilson@ravel.udel.edu (James Wilson)
Subject: Re: Iris
Date: 17 Jun 92 19:41:19 GMT

copler@iuvax.cs.indiana.edu (judith copler) writes:
> My bearded iris have developed yellow/brown blotches on some of the
> leaves.  It isn't too unsightly and there seem to be many healthly
> leaves as well.  Last night when I was cutting off dead flower stems
> I discovered that some of the outside rhizomes are mushy (pudding
> consistency) and have a rank odor.  This stand has been in place
> about 3 years and the soil is mostly clay.  It is near the birdbath
> so may get a little more water than other areas of the garden.  Any
> ideas on what the problem is and how I might treat it?  

The yellow/brown spots could be any of a few ills that bother iris--
fungal leaf spot, borer damage, or mosaic virus, so it is hard to know
for certain without a fuller description.  What is often helpful is to
compare them to pictures available from your local ag extension
office, local iris society, library, or even the Ortho reference if
the others aren't easily accessible.  The other symptoms point
directly to bacterial soft rot.  For that, you should physically
remove all of the soft parts--scrape them out with a spoon.  Spray the
area with agricultural streptomycin.  (Some people swear by sprinkling
Comet with chlorinol around instead.)  Do what you can to make sure
the sun can get at what is left.

Sometimes you will lose the whole plant, sometimes not.  Among iris
circles there is considerable anecdotal evidence that some varieties
are more susceptible to rot than others, but I haven't seen a thorough
study of that.  This year's weather was worse than some years for that
here in Delaware.  Ideal for beardeds is a moderately wet spring and a
moderately dry summer.

For prevention, bearded irises need help in dealing with clay soils.
Be certain not to mulch them, do keep weeds down, remove old leaves
and debris.  When planting, maybe add some organic matter (but keep pH
up around 6.8) and maybe sand.  Plant the rhizome with its top at or
even above the soil line so the sun can help you out.

If you have an area that is likely to be continually wet and want to
grow irises, putting in some Japanese iris might be a good choice.
They like sun, somewhat more acid soil than the bearded, and lots of
water, and they'll extend your bloom season.  Siberians work somewhat
in that way too.  If you want to see lots of Japanese irises in
action, the national convention is in Kalamazoo, Michigan June 26-27.