Subject: Re: Old Wives, water droplets was FROST

Subject: Re: Old Wives, water droplets was FROST
Robt R Pries (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

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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