cabbage problem

 as we bench grow mainly all our veg seed including brassicas  we planted out our cabbage plants good strong plants pot grown doing well then we noticed the leaves where turning yellow and although we had planted 3 raised beds all netted but not environment mesh on closer inspection it looked like aphid infestation so sprayed the plants with Bug Killer on all the 3 beds that where infested

we have infestation on a late  kale crop last year and then composted the crop it was  also on the the sprouts but after spraying the sprouts with a garlic spray mixture my own mix it seemed to get rid of the aphids but I've never had aphids on early brassicas before they only seem to come later on in the growing season ?

so to deter  these pests is spraying the best way a residue spray would be best me thinks  ? or invest in environment mesh but  if  needs be I mite have to possibly try my old method of a mix of a garlic spray unless anyone can give me some sound advise about getting rid of those damn aphids

actually the plats where perfect when they where planted the infestation came after plantings when the plants started to grow so it looks like spraying will be the norm at it looks like its going to be trial and error with available sprays to see what performs the best including my own garlic spray