I am currently trying a spray that in theory will resist slugs, snails, catterpillars and kills the likes of blackfly.
I can say after watching a slug last night crawl upto a sprout leaf, then what looked like about to take bite then turn into a ball (I suspect in pain) and promtly crawl away again I would say on slugs it worked.
So the recipe.
2 orange peels
1 garilc clove
good sprinkling of black pepper
2 really hot chillies (I use chocolate trinidad scorpion)
chop up and put in a pan (windows open) and bring to boil and simmer for about 20 mins. Leave overnight to steep.
Put into blender and whizz up. This will make about 500ml of puree.
Now when your ready add half to a jug and then top up to 1 litre and add 1 Tspoon of liquid soap.
I then give a good stir and pass it through cloth into the spray bottle.
It seems to last a while even when it rains.