I am always very careful whenever I apply isopropyl or any pesticides on
my plants. I take the plants out of the greenhouse, apply the pesticide, then
let the plant sit in the shade until the leaves are dry. Then I put the plant
back in the greenhouse. On overcast days this procedure is not necessary.
I've never used isopropyl in a spray bottle. I only apply it via cotton
swabs. It is very effective this way. It sounds like we have both
gravitated towards the same solution. A few years ago I tried several
different ways to kill the aphids on my wife's chile pepper plants, using
isopropyl. I'd put some isopropyl on a rag, and cover both infested plant
and rag with a plastic container---in essence I was making a kill chamber
similar to those used by entomologists in the field. Well, I killed bugs
and several chile plants. I would have continued with the experimentation
but I was stripped of funding (Bridgett didn't like my killing her plants).
Rob Maharajh, the chemist, has told me that the burning is due to a kind
of frost damage produced by the vaporizing alcohol (like the chilling
you get from acetone and other organic compounds). I find this hard
to believe, but I'm no chemist.
Barry