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 -