White fly

Can anyone suggest an organic way to stop or reduce this pest on kale, sprouts cabbage?
This year I bought 2 ‘packets’ of biological control (Encarsia) with a 2/3 week gap and released them underneath environmesh but that made little or no difference. I wonder if there was just already too many whitefly? Has anyone else tried this?
The RHS recommend the following organic pesticides:
– Plant oils (Vitax Organic 2 in 1 Pest and Disease Control, Scotts Bug Clear for Fruit & Veg).
– Fatty acids (Bayer Organic Pest Control, Doff Greenfly and Blackfly Killer).
– Plant extracts (Growing Success Fruit & Veg Bug Killer, Growing Success Whitefly Killer, Agralan Whitefly Killer).
– Pyrethrum (Py Spray Garden Insect Killer concentrate, Scotts Bug Clear Gun for Fruit & Veg).
Any experience anyone? I haven’t tried any but I prefer to avoid any spray if possible.
Thanks
Dave