Easiest and safest way is to use diatomaceous earth. Totally inorganic - not a poison and you can dust it all over your plants and fruit/veg up to harvest time .. just wash it off. It's been used for years as a dewormer for livestock as well. You'll be wanting what's called 'food grade' DE - or one that does not have a bait in it. Only con is that it is indiscriminate about what it will kill, so when you dust try not to get any on the flowers that bees will pollinate.
I use DE in my potting mix as it keeps ants from colonizing pots. Even if it is wet it will work though you will have to reapply to leaves and ground after it rains since the rain will wash it off.
To insects, DE is like walking through shards of glass - for hard body insects it actually scratches of the waxy substance on their shells causing them to dehydrate - also when they groom themselves after walking in it they ingest it and it will tear up their digestive system. That's how it kills soft body insects.
This stuff is amazing .. it's totally knocked down a severe whitefly infestation in 2 days.
