Re: nicotine - I can't think of a less appropriate heading for discussing it, since the whole point of this thread (including my posts) is to avoid sprays - but I'll get round to it here by the end...
I can cover both viewpoints by heartily recommending everyone gets a copy of Lawrence D Hills' "Grow your own fruit and vegetables" it is recently reprinted and I think it's one of the books they can print on demand at Waterstones etc.
It is a brilliant trove of useful cultivation techniques and includes last-resort recipes for home-made solutions against fungi & insects etc.
It is also an organic book from the time when organic growing was a science not a religion.
To make that clearer - anything based on doubt is a science, real science always doubts itself. Any scientist who tells you something's true is probably a very senior one - ie. a politician who occasionally wears a lab coat.
Anything based on what somebody thinks should be true ISN'T SCIENCE (even when, very rarely, it turns out to be true - actually I can't think of an example).
LDH's book is the best antidote to the extremist views we are trapped between as Gardeners - "Anything for a buck" on one hand and on the other hand those who say "never take any risk ever" and "every bug is sacred - save the smallpox virus for posterity".
Still, I don't recommend using nicotine because it can have unforseen consequences.
Even though you have a good idea what it will do to the place it goes (unlike modern synthetics) and have a good idea how long it will take to dissipate (very, very, unlike modern synthetics) you still don't know it won't kill your garden 'pals'.
With nicotine a dying caterpillar might poison a robin even if a dead one won't kill a frog the next day. You won't be condemning your pals or their offspring to a slow death by some neurotoxin that only appears two or three stages down the decomposition, but they might die directly through Murphy's Law. The only thing you can be sure of is that it won't end up in the top predators (hawks, foxes, you, me).
Anyway, here's a link from the US to the same recipe as LDH's:
http://www.aselfsufficientlife.com/nicotine-spray-insecticide.html - READ THE ADVICE.
I know this may sound pompous and patronising but forgive me - IF YOU DON'T KNOW WHAT THE DARWIN AWARDS ARE THEN DON'T USE THIS SPRAY - I mean it... Look them up on Google, have a good laugh, sit down and re-think.
Any spray that can make insects sick is a major escalation and should only ever be used as a last resort. Never spray before sunset or the bees might get it (though at least the hive won't accumulate nicotine). Sprays that drown pests (soaps) should be tried first because they only hit what you see at the time.
LDH also suggests not making too much at a time because "the safest way to store nicotine is as cigarette ends". Very good advice - it highlights the fact that the flavour of the mixture is the best defence against anything or anyone swallowing it. This was one of the problems with the commercial mixes in the past - though the one mixed with quassia was excellent - it tasted even worse...
Bear in mind that nicotine can go through the skin - fast - so don't let it come into contact with any skin - bare or otherwise - especially thin skin. NEVER WORK IN SPRAY DRIFT OR SPRAY IF THERE'S ANYONE DOWNWIND. A few drops on your fingers won't kill you but wear rubber gloves anyway. It works fast and people's tolerance of nicotine varies wildly - if you get any hint of classic 'first cigarette' symptoms then stop immediately.
Adding soapflakes or soft soap (another 'foliar feed' in its own right) will help against caterpillars.
Good luck and REMEMBER THE DARWIN AWARDS.
PS. The only good thing about Murphy's law is that it occasionally has to work against itself - but it only does that to lull idiots into a false sense of security...
