I think it really helps if you've got loads of other non-crop stuff growing, that's my excuse for not weeding so often anyway!
For example, I had a small outbreak of greenfly in my greenhouse earlier in the year and was considering how to treat them when I saw I had some little white grubs on them which turned out to be hoverfly larvae happily munching the greenfly!
I've also got hedgehogs and loads of frogs helping to keep the slugs in check, which I also try to kill off using beer traps. Oh and I've also got slow worms and even common lizards all doing their bit too!
So pest control hasn't been a major problem this year but I expect it won't always be so easy. next year I'll be planting some marigolds and other flowering plants to encourage more hoverflies and bees though.