[JayG]

it would be an idea  to explore the method of the commercial growers and how they manage to grow 40 acres of brassicas  without a slug or caterpillar in sight

Commercial growers are allowed to 'treat' their crops with all sorts of (permitted) chemicals to save them having to buy up the world's supply of Environmesh to achieve the same result - we amateur growers aren't allowed to use such chemicals these days - sometimes it can make life difficult, but at least you know that you don't have to wonder what else you might be swallowing with your coleslaw!   

[compostqueen]

Yup, which is why I shall always grow my own 🙂

[AnneB]

I seem to do quite well with cabbage of all types and sprouts.  Less success with cauliflower though.  I do net them, which is a bit of a faff, but savoys and other types are alaways good.   We have slightly acidic soil and they seem to quite like that.   I don't find them much trouble to me honest.