Re: CULT: Leaf Removal & Soft Rot

In a message dated 1/28/2003 7:32:37 AM Central Standard Time, 
charandmike@juno.com writes:


> > We do know that Erwinia caratovora growth rate is temperature 
> > dependent.
> > We do know that the growth is moisture dependent.
> > We do know that the growth is pH dependent.
> > We even know the ranges of some of the above factors.
> > I have found no information concerning UV effect on growth rates but 
> > suspect 
> > it may be significant from kitchen table stuff, garden stuff, and 
> > plant 
> > tissue culture stuff.
> > 
> Bill,  Please elaborate on the statement about PH dependent. I have some
> thoughts about that and would like to know more. 
> 
> Thanks
> Char Randall
> Melba, ID 
> 

Following are some excerpts from an upcoming, not yet complete, Old South 
Iris Society news letter. If you (or others) will send me a mailing address 
off list, I will be happy to forward a copy to you when the article is 
complete. Most of the info is gleened from source not specific to irises but 
still applies to the iris world nemisis. I'll be out of town for the next few 
days. I will elaborate further upon my return.

Erwinia caratovora pH growth:
The minimum pH in which the bacteria will grow is 5.6
The optimum  pH level for the bacterias growth is 7.1
and the maximum pH level in which the bacteria will grow is 9.3
as per some university published data.

Irises will survive, but not well, below the 5.6 pH range but reach their 
best growth rates above a pH level of 7 and above. Too, irises grow 
reasonably well in the 9.3 to 10.5 pH range. So one experiencing excessive 
rot problems might logically consider elevating (or lowering) the the pH 
level of their soil until they are satisfied with both the growth rate of 
their irises and the incidence of rot. Since other factors also influence 
erwinia c. growth as well as irises, we might reasonably expect to adjust pH 
levels in our individual gardens to meet our specific conditions (rainfall, 
etc.) in a way that minimizes soft rot incursions.  Apparently the growth 
rate of erwinia c. approximates the normal distribution curve slightly skewed 
toward the lower pH ranges.

Erwinia caratavora is non-spore forming. In laboratory conditions it will not 
grow above 36 degrees C.( 96.8 degrees F). Sadly, it is not only active but 
can grow and increase over a wide range of temperatures- from 3 to 35 degrees 
C. ( 37.4 to 95 degrees F). The bacteria is killed by extended exposure at 
about 50 degrees C. (122 degrees F). I have not yet determined the 
feasability/survivability of extended exposure of iris rhizomes to this 
temperature but do expect to do so when rot season arrives.

I have an ailing friend and the only thing I dislike loosing more than 
flowers are friends. I will address moisture issues when I return in a few 
days.

Smiles to all yawl,
Bill Burleson 7a/b
Old South Iris Society

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