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Re: CULT: leaf spot

  • To: Multiple recipients of list <iris-l@rt66.com>
  • Subject: Re: CULT: leaf spot
  • From: Linda Mann <lmann@icx.net>
  • Date: Sun, 8 Feb 1998 20:41:25 -0700 (MST)

Walter Moores wrote:
>         I am glad to see the soil mentioned in this discussion.  I think
> where the soil is heavy clay and not tilled, there is less leaf spot??
> If the soil is sandy loam and tilled, there is more soil splashed on the
> leaves and therefore more leaf spot??

And Edmundas Kondratas wrote:
> But you must know, that except humidity lack of phosphorus =
> and lime in the soil increase danger of disease. 

My two cents about soil, cultivars, nutrients, and spots - I walked
around the 'garden' looking at foliage today.  Everything has at least
one spot on mature foliage - some have black spots on dead foliage, some
have brown spots on live foliage.  Even I. pallida has a few spots.  But
during the growing season only a few cultivars are spotted badly enough
that the plant seems to be severely weakened by the disease (2 come to
mind - APRIL IN PARIS and LEMON MIST) and that usually hits after bloom
season.  Today, I notice the least winter injury and the least spotting
on plants overgrown by fescue grass (Festuca), not exactly the best way
to nurture irises.  

In the southeastern part of the United States (sub-tropics) phosphorus
and lime are leached from the soil by high rainfall amounts (50+
inches).   So annual replacement is needed here.  With a dash of
nitrogen for protein to feed the bugs.

Aphids are favorite lunch menu for ladybug larvae - there are lots of
ladybugs here in normal spring/summer and I have never noticed aphids on
my irises other than this month, right before the snow.  I hope they
caught the flu.

As someone observed before (maybe Griff Crump?) - keep the irises happy
and healthy and they won't be as prone to get fungal or bacterial
problems.  And that includes good nutrition and minimizing damage to
roots and foliage (my personal opinion - though some cultivars seem to
thrive on being dug up).  The most disease-free iris plants I have ever
seen around here are in a garden that doesn't get hit much by late
freezes, is cultivated by hoe/mattock, has fairly crowded plants that
are thinned mercilessly during bloom season-sales, and is sprayed with
insecticide (Sevin) regularly 'to prevent rots and blights'.  So I think
that while the soil may contain the spores and bacteria, the bugs (or
freezes or droughts, hail, earthquakes, etc) cause the injury that lets
the infection get started.

Linda Mann east Tennessee USA
I have had WAY too much caffeine today!

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