John Kempf has done some blog posts and podcasts on aphids. His approach is that aphids attack plants due to excess nitrates or ammonium in the sap, and excess NO3 and NH4 is caused by a lack of available magnesium, sulfur, and molybdenum in the sap (with phosphorous and boron having some benefit too but not directly related to nitrate conversion into protein and amino acid). The Mg, S and Mo when in the sap at adequate levels help the plant in this nitrate conversion process. I have experimented with this approach on my fruit trees and roses and found that it did work after a couple of foliar sprays about 10 days apart. But from a holistic viewpoint, I also try not to overwater during peak aphid season as the excess growth from excess water will cause excess ammonium in the sap (I have confirmed this with sap testing). And, I want to keep weeds and/or cover crops in the area and watch them, as my goal is to have my crop healthier than the weeds or cover, and I watched the aphids move from my crops to my covers/weeds after the above foliar sprays. The covers also help keep beneficial predators around. I have lots of predator wasps and flies around and ladybugs too and those feed well on the aphids. I try not to spray to kill the aphids, but I have done a raw unfiltered neem oil spray rarely if I feel I need a knockdown.