Yep Your'e right. Its an item from America, which does have source.
Unfortunately I only wanted to show that the only way to be sure of
things is to check again. I had heard that fungal diseases are spread by
water on leaves, and that the "burning" is caused by other things. At
times we dont stop to think and accept folk lore as factual, due to it
being passed on from father to son etc..
It pays with gardening to find the real facts, and while the internet is
a great source of diversity, it does need to be checked against known
sources of information. This item I believe came from such a source, but
I forget where (Sorry I am also an unknown) We can be pedantic, but I
feel that now our attention has been drawn to this, other can check to
verify, as there are still others spreading the information that water
"burns" leaves. It isnt so! It affects it in other ways. I believe that
the spreading of fungal diseases with wet leaves is much more likely,
and makes more sense....

David Hare-Scott wrote:
"Jonno" wrote in message
...
EXAMPLES OF GARDEN “MYTH”-INFORMATION

..snip 9 items....

Here are some final considerations as you evaluate the vast resources of
knowledge:

* Consider the source.

Of the 9 items none quotes a specific reference and only 3 quote the
institution responsible for the information.

* Does other data support their conclusion?

None of this analysis quotes supporting evidence and most don't even specify
the primary reference.

* If there are only testimonial and no data, or appears to be more
hype than hypothesis, buyer beware!

There's much of this about!

* And lastly, make sure the data is relevant to your climate, soil,
and ecological conditions.

Quite so. Sadly this data, or qualifications relating to it, are also missing
from the quoted cases. The case refering to the use of gypsum refers to "our
foothill clay" as being significantly different but we have no idea where this
is or the nature of such clay.

OTOH there are many myths around in the world of gardening and telling people
to be wary cannot be bad. Some of the cases mentioned probably do have better
information than the myth they are setting out to debunk. Sadly the author
only goes part of the way towards doing what they set out to do.

David

Here's a link and part of a theory, which backs up what I read.

http://cahe.nmsu.edu/ces/yard/1999/062899.html

But wait I think there's more...

Jonno wrote:
The water on the leaves story has been around for some time, and been
investigated. The problem is really caused by fungal infections due to
water on the leaves. The sun does not magnify due to different focal
length. But plants can suffer from straight out sunburn....Tomatoes for
instance get sun scald.

I'll try and find the story again if I can...

I wonder if some plants are susceptible to the pyrethrum?


Blackadder IIVX wrote:
"Jonno" wrote in message
u...
Maybe you burnt them due to the gas being a sort of refrigerant. In
other words youre spraying a bit too close to the plants.
Do it when there is no winf ie early in the morning when theres
very little wind. Then you can spray them with some distance in between.

Oh no. I use the hand pump manual add ons. I don't use a spray can.

Its just the heat of the sun. Even if you just spray cold water on
the plants- the sun magnifies the droplets and burns the plant.


John Savage wrote:
"Blackadder" writes:
Do you use the spray during the day?

Probably about mid-morning on a sunny day.

I used a similar spray and it ended up burning my roses - but it was on
account of the sun's heat. If I had done it in the evening or very early
morning it doesn't happen.

I'll bear that in mind. But I would expect there to have been on the
pack a prominant warning of possible plant damage. I'm surprised that
the matter hasn't been brought up on this group before.

Interesting diatribe but as it was posted as a follow up to my post I
should clarify that I was suggesting that excess spraying with oily
compounds like pyrethryns on a hot day could result in similar
problems associated with spraying with petroleum based oils. Nothing
to do with the issue of water droplets on the leaves.

On Dec 12, 8:13 pm, Jonno wrote:
EXAMPLES OF GARDEN "MYTH"-INFORMATION
SNIP
Myth#4 Watering on a sunny day will burn plants.

The premise here is that water droplets magnify the sun's rays and burn
the leaves. Hmmm, let's see! Do plants burn when the sun comes out
after rain? (There wouldn't be much left in the tropics then...) Desert
farmers routinely use overhead sprinklers to cool and protect young
plants from drying out. This myth may have come from the observation of
applications of water high in dissolved salts. As the water dries, the
salts left behind can burn the leaves.
SNIP

Andrew wrote:
On Dec 6, 11:32 am, "Blackadder" wrote:
Do you use the spray during the day?

I used a similar spray and it ended up burning my roses - but it was on
account of the sun's heat. If I had done it in the evening or very early
morning it doesn't happen.

BD

Pyrethrins are also quite oily which probably intensifies the problem
of spraying in hot weather.- Hide quoted text -

- Show quoted text -

I suppose you have thoroughly tested the situation, that is, is what you
say causes the problem? Theory is all well and good, but if the facts
are not checked Then the community goes on to pass it on as "fact" (This
does not mean you are not correct) The same happened with the water on
leaves enlightenment, when it was shown not to be so a time ago, but
people kept coming up with the same story as it was so ingrained, and
such a wonderful "revelation" based on nothing more than observational
theory...


Andrew wrote:
Interesting diatribe but as it was posted as a follow up to my post I
should clarify that I was suggesting that excess spraying with oily
compounds like pyrethryns on a hot day could result in similar
problems associated with spraying with petroleum based oils. Nothing
to do with the issue of water droplets on the leaves.

On Dec 12, 8:13 pm, Jonno wrote:
EXAMPLES OF GARDEN "MYTH"-INFORMATION
SNIP
Myth#4 Watering on a sunny day will burn plants.

The premise here is that water droplets magnify the sun's rays and burn
the leaves. Hmmm, let's see! Do plants burn when the sun comes out
after rain? (There wouldn't be much left in the tropics then...) Desert
farmers routinely use overhead sprinklers to cool and protect young
plants from drying out. This myth may have come from the observation of
applications of water high in dissolved salts. As the water dries, the
salts left behind can burn the leaves.
SNIP

Andrew wrote:
On Dec 6, 11:32 am, "Blackadder" wrote:
Do you use the spray during the day?
I used a similar spray and it ended up burning my roses - but it was on
account of the sun's heat. If I had done it in the evening or very early
morning it doesn't happen.
BD
Pyrethrins are also quite oily which probably intensifies the problem
of spraying in hot weather.- Hide quoted text -
- Show quoted text -