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
lenght. But plants can suffer from straight out sunburn....Tomatoes for
instance get sunscald.

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

I wonder is 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.