Subject: Re: Old Wives, water droplets was FROST

Robt R Pries rpries@sbcglobal.net
Wed, 14 Nov 2007 08:41:57 PST
Tony, Good Stuff. I suspect a little oedema might be
welcome if it was the result of a break in the
drought. I was down looking at my property and ammazed
at how well the trees seem to be withstanding the dry
conditions but read in the Carolina Gardener that I
should expect many to die next spring.  

--- Tony Avent <tony@plantdelights.com> wrote:

> Bob:
> 
> I don't have an old wife, but will tackle these
> tales as it relates to 
> agaves.  We have two water issues that cause severe
> foliar damage.  If 
> we have several days of rain in the fall or early
> winter as the growth 
> is slowing, followed by bright sun, we can get
> terrible leaf scorch due 
> to Oedema.  .
>
http://plantclinic.cornell.edu/FactSheets/oedema/….
> 
> 
> The other water related damage occurs after either
> an ice or snow storm 
> that leaves frozen water on the leaf surface.  When
> the sun reappears, 
> the tissue beneath the ice is scorched due to the
> magnification of the 
> suns rays through the water.  No damage occurs where
> the ice or standing 
> water is in the shade.  Over the years we have seen
> such damage on other 
> plants, but none as severe as we see with agaves.
> 
> Tony Avent
> Plant Delights Nursery @
> Juniper Level Botanic Garden
> 9241 Sauls Road
> Raleigh, North Carolina  27603  USA
> Minimum Winter Temps 0-5 F
> Maximum Summer Temps 95-105F
> USDA Hardiness Zone 7b
> email tony@plantdelights.com
> website  http://www.plantdelights.com/
> phone 919 772-4794
> fax  919 772-4752
> "I consider every plant hardy until I have killed it
> myself...at least three times" - Avent
> 
> 
> 
> Robt R Pries wrote:
> > Jonathan wrote;
> >
> > " It doesn't really make sense, as I think about
> it,
> > and I suspect you'll
> >  agree, that the sun's heat would lead to
> increased
> > chilling of the
> >  leaf under where the waterdrop was located--it
> > wouldn't evaporate any more
> >  rapidly than the sun's heat caused it to
> vaporize."
> >
> > I am a bit on shaky ground since I am not a
> physical
> > chemist, but as I understand the phenomenon.
> Sunlight
> > can increase evaporation and although there is a
> > direct relationship between light and evaporation,
> > calories may be drawn from the surrounding
> > micro-environment and not just the sunlight as the
> > water changes state. Since there is a
> proportionally
> > huge consumption of calories required some of
> these
> > may be drawn from the leaf. The sunlight may not
> be
> > the only source of heat for the evaporation and
> may
> > facillitate the process by affecting surface
> tension
> > and other factors. Thus the immediate area of the
> leaf
> > may be chilled because of its donation of heat to
> the
> > process. Perhaps we are both saying the same
> thing.
> >
> >
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