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Re: CULT: Leaf spot


I did a google search for <leaf spot life cycle> and got quite a few
hits for university and agricultural extension publications.  Most of
these are about fungal leaf spot, so I did another search for <bacterial
leaf spot life cycle>.  Most are about plants other than iris - I was
curious to see if the fungal and bacterial leaf spot life cycles were
similar among various kinds of plants.

Bottom line is that the life cycle & management for all types of fungal
leaf spot organisms on all kinds of plants is about the same, except, to
my surprise, that there are differences between colder vs warmer
climates, at least for some fungal critters (has to do with a stage of
the fungus that is only present in colder climates - they don't need
that stage here where they have green leaves to live on all winter).

Spores come from soil, dead leaves, or other infected plant parts, are
spread by wind, water splash, or as projectiles from fruiting bodies (I
don't know if this last mechanism applies to iris fungal leaf spot, but
does to some of the other fungi).

Once the spores land on the iris leaf, they grow if the leaf is wet and
enter the plant through stomates in the leaf.

Bacterial leaf spot, primarily our old friend, soft rot  (Erwinia),
behaves about the same, except for the projectile fruiting bodies and
differences between cold and warm climates.

Both Erwinia and fungal leaf spot can persist <inside> the plant tissue
(roots/stems and leaves), waiting for injury or stress to get them
growing again.  That was something I didn't realize.  Both can be spread
many miles by wind, so will always be around, waiting for ideal
conditions.

I'm not sure how to tell fungal leaf spot from bacterial leaf spot,
except that fungal leaf spot is a problem in cool wet weather, and
bacterial leaf spot is a problem in hot wet weather.  The <summer crud>
I've mentioned seems to be Erwinia.  My dining room table reeks of soft
rot where salvaged seed pods are drying out.

I make a concerted effort to get rid of anything here that is
susceptible to soft rot that becomes bad enough to attack rhizomes.
However, nearly all my irises here at the house show some degree of leaf
spot injury this time of year.

I haven't looked at the TBIS website yet - apologies if this is a repeat
of what it says.  I had fun learning new things about these nasties.

--
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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