My butterfly netting around my purple sprouting has successfully kept out the Cabbage White and pigeons. However, this afternoon when I went into the cage to pick some, I noticed quite a few whiteflies had taken up residence. The netting is too close knit to allow ladybirds in to feed on them and I don't want to use any sprays so as far as I can see, the best way to control them is if I cut the leaves off that have the eggs and young and feed them to the chickens. If I take an electronic fly zapper into the cage, I should be able to destroy the flying ones.
I may have to go on a ladybird hunt and put them inside the cage to spend the winter there. I could make a couple of ladybird houses and hang them on the upright supports. Hopefully, they will overwinter and come out in the spring to feed on any whiteflies that I have missed.