I've always been plagued with white fly round brassicas at this time of year, often getting a face full when bending down to weed. This year I invested in debris netting and (touch wood), I noticed there is a distinct absence of the beggars. Having said that, this entire year I've hardly had any aphid problem especially blackfly so it might be a location thing. Last year was very wet, followed by a long cold spring and this year we seem to be having a mini drought here.
I'm surprised by the problems on marrows, courgettes and french beans - but would you really want to throw a systemic killer on these crops as you'll then be eating the produce
![wacko :wacko:](https://chat.allotment-garden.org/Smileys/green/wacko.gif)
Are you sure it is aphid (green, white or black) as the soap treatment really should work - how often are you treating? If I got an infestation, I'd treat one day, and again the next, and again a couple of days later paying particular attention
under the leaves where some may get missed and replace those that you managed to kill in a very short space of time.
As for treatments, I try to avoid pesticides as often these kill garden friendly bugs that eat the aphids (like ladybird and their larvae) as well as bees which are already on a serious decline. The only time I might use an approved pesticide is to rescue woody plants like fruit bushes (especially from sawfly) and only after I've done the soap treatment first. The more you use pesticides, the fewer friendly bugs you have around so encourage infestations.
Sorry I can't be of much more help and not what you wanted to read