Re: Re: CULT: leaf spot

Thanks, Linda -- I have lime and may give it to them next time around. -- Griff
----- Original Message ----- From: "Linda Mann" <lmann@lock-net.com> 
To: <iris@hort.net>
Sent: Monday, January 07, 2008 1:20 PM
Subject: [iris] Re: CULT: leaf spot
Griff, leaf spot is nearly always rampant in my low lying growing area, but was almost non-existent this year, thanks to the drought. Until it finally started raining again last month.
I've always assumed the fungal spores of leaf spot and bacterial rot 'starter' cells were everywhere, just waiting for the right conditions to grow.
Here, constantly damp foliage from dew in a "normal" year (whatever that is anymore), high humidity, and damaged foliage (i.e., from freezes, insects, hail, deer, hurricane force wind, etc) are a great recipe for spot and rot.
Best way I've found to prevent it is to put plants in a humidity controlled environment ;-) or get plants with natural resistance.
When conditions are <really> bad, even the resistant ones get some leaf spot.
Maybe do as Neil M. once suggested I do - buy a giant fan to keep the air circulating and foliage dry. Build a greenhouse over them complete with dehumidifier?
Things that seem to help some (but not eliminate entirely) - less fertile, drier soil (lush growth is usually more susceptible to damage of all sorts and subsequent disease); crushed/powdered dolomitic limestone (limestone with some of the calcium replaced by magnesium). Barry B and I think some others have said that the limestone helps and I had already thought that. So we must be right ;-) 

<Despite our severe drought this year, they
flourished exceptionally and went into the winter looking green and great. I checked them yesterday and found every bed covered with the worst case of leaf 
spot I've ever seen.  The beds were heavily augmented with new soil when
planted. I wish I knew what brings it on and how to prevent it (not cure it), 
if it can be done.  --  Griff>
--
Linda Mann east Tennessee USA zone 7/8
East Tennessee Iris Society <http://www.DiscoverET.org/etis>
Region 7, Kentucky-Tennessee <http://www.aisregion7.org>
American Iris Society web site <http://www.irises.org>
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