I have an aphid problem. In Michigan, they attacked my tomatoes, and I did a great deal of squishing. (I never found the method of blasting them off with a jet of water very effective.) In Japan, they are attacking everything - swiss chard, nasturtiums, parsley, cilantro, johnny-jump-ups - on both porches. Birds and bugs (neither of which I can identify at this moment) are helping as they can, but when they attacked my kale seedlings I drew the line.
Aphids reveal themselves in spring and will hang out for a whole season if one is not attentive. They will overwinter in woody plants, so diligence is required for a season or two to say the least. Much to my dismay, they at some point develop wings (hellish things), and fly off to find a new buffet. Ants will apparently also move them about since the ant enjoys the honeydew the aphid desposits as it snacks.
I read that a strong chamomille tea would encourage them to leave, so I thought I'd give it a shot. (I can't find a reference now for that, but suffice it to say the tea is made.) And after I spotted them on my kale seedling, things got ugly. The pitcher contains not only chamomille tea, but three hot chillis, two bags of mint tea, some cilantro, and some fresh mint. I added water to all of this and set it out in the sun to brew. Oh, and some nasturtium blossoms that needed to be pinched. (There are a variety of home remedies for assorted bugs and diseases that are worth checking out.)
It looked quite pretty as it started, and now it looks downright lethal. I plan to use a small amount mixed with water and dish soap, and we'll see what happens. My only fear is that I may have created a plant killer as well.