1 pint of 4 lb Methyl Parathion or 0.75 lb of Orthene 90 S, better 1 lb. controls them, too. Bifenthrin at 5 oz is also good, but a third choice. Methyl, I believe, is only available in 15 gal "totes", or returnable containers. Orthene stinks them to death! You'll have to check for labeling in your state.

We have aphid problems in cotton, but I have not noticed them at damaging levels in soybeans down here, so I can't say what you can get out of those products toward controlling them. In cotton, we get a naturally fungus that takes them out in mid to late July.