Subject: Re: Old Wives, water droplets was FROST
Tony Avent (Wed, 14 Nov 2007 08:26:57 PST)
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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