Posted: 13/05/2012 at 22:55
I think the use of washing up liquid added to water in a spray to kill aphids is an urban legend. It may well kill the aphids but you also risk losing your plant if too much is added to the water sprayed on the plant.
If it is blackfly and a large infestation then cut off the most affected shoots, the bugs will have sucked the sap from the leaves and even if you use a spray which kills the bugs the leaves left will be distorted, you'll also have less bugs to kill.
Aphids - black/greenfly breath through their skin. I use a mix of olive oil, crushed garlic and warm water to spray them with, the oil blocks up their lungs, not sure what the garlic does, it's possible they don't like the smell, the warm water dilutes the oil.
Is the plant a tree or shrub? Do you also have ants and are the bugs just on the one plant?