With great difficulty! I got my Dad to make some wooden frames to go over the kale and I've got the green shade netting fastened to the frame. Caterpillars still occasionally get in though, I have to vigilant and check the plants regularly, picking off any that I find.
Sound like netting is the way to go then but if I net now, won't I risk trapping all the little feckers inside with a free meal? I suppose the solution is to give the plants a good going over before applying net
You could give the leaves a really powerful spray with a jet of water from the hose then check over manually. Netting is really useful, not just for caterpillars but pigeons which will strip kale to the bone given half a chance.
Don't forget the slugs, snails, and cabbage root fly too!
Basically, with veg... if we eat it, so do billions of other beasties. I net all my brassicas and roots at my allotment with enviromesh, and things still somehow get in there!
The pigeon thing is weird - they seem to like brassicas at a certain stage, at which point they will tear them to ribbons virtually overnight. My neighbour didn't net his cabbages and for aaaages they were absolutely pristine. I wondered if my netting was a bit overkill. Then all of a sudden, they were reduced to cabbage skeletons.