Re: CULT: Leaf Removal & Soft Rot

In a message dated 2/13/2003 11:35:57 AM Central Standard Time, 
jbruce1@cinci.rr.com writes:


> In respect to the differences between field and lab conditions,
> most home (inexpensive) pH meters are grossly inaccurate
> and will vary quite a bit. Color test strips and chemical tests
> will also vary widely because of  age of solutions, droplet sizes,
> age of test strips, and human factors such as ability to match
> color, contamination, etc.
> 

The casual reader of this thread might think we differ greatly on the subject 
matter. Like you, I have a strong belief in soil testing. Home soil nutrient 
test kits fail miserable here, partly just because I spill stuff and other 
times because they are so tedious to use. For garden purposes, I find pH 
meter performance accurate enough and accuracy easily tested. All of us 
recognize some iris will do better with a change in location where a 
different soil pH may be encountered. Too, we agree that more than a few 
irises will grow outside conventionally accepted "ideal" pH ranges.

As for measurements-Errors in sampling techniques, collection, and 
preparation contribute far more to error in nutrient/pH measurements than do 
meter errors. Your procedures/mixing do not indicate lack of attention to 
necessary details. In short if we do not collect and prepare a representative 
sample we had just as well not collect a sample at all.

Stress is indeed a factor in Erwinia c. susceptibility regardless of whether 
it is caused by physical damage, a weakened condition induced by 
environmental factors, or gardener induced. As I suspect are genetics. 
Weakened plants lack full capacity to defend themselves. Certainly soft rot 
can occur anywhere, particularly if we accept the premise that it is 
distributed in soils world wide. But still, for the bacteria to manifest 
itself in iris rhizomes in a significantly damaging way, conditions must be 
conducive for the bacteria's growth.

While the genetic components (arguably it exists) are in the hands of 
hybridizers, the factors controlling both Erwinia c. and iris growth are 
largely in the hands of gardeners. Of the ones that can be controlled pH is 
relatively easy. Suberization of rhizomes is also relatively easy. To some 
degree moisture is controllable. Irrigation at times of favorable soil 
temperatures for Erwinia c. growth can be avoided. Subsoiling can place 
available moisture necessary for the plant (and bacteria) further away from 
the rhizome at times when temperatures are most conducive to Erwinia c. 
growth. While we not be able to control rainfall, we are remarkably capable 
of controlling the vertical and lateral components of drainage. Soil 
amendments may be varied to influence moisture retention/removal. Temperature 
is controllable to the degree that moisture addition/evaporation and/or mulch 
placement/removal might be used to influence it. Insect damage and other 
plant stress is certainly controllable to a degree.

The dilemma we face is what level on any factor under our control is most 
beneficial to irises and least beneficial for soft rot at a given time of the 
year? I expect we will be struggling with this dilemma for some time. 
Research under controlled conditions is the only practical way in which we 
might hope to separate the various growth factors into meaningful, useful 
data for irises. I remain pro controlled research. Both lab and field. For 
our gardening observations to have any validity, soil testing is mandatory.

Chlorine dioxide is showing some promise as an effective control outside of 
the iris world and perhaps holds promise for us.

Smilin', wonderin' and knowin' that some years ask questions and some years 
answer 'um,
Bill Burleson 7a/b
Old South Iris Society

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