I found these recipes from this site...
Home remedy for aphids. You can kill aphids by spraying, especially under the leaves, with a solution of 2 tsp mild dish or laundry soap to a bottle of luke warm water. The soap washes off the aphid’s protective waxy coating and causes dehydration. You can also mix three parts luke warm water to one part vegetable or horticultural oil and a couple drops of dish soap. This mixture can be sprayed on to clog the respiratory spiracles of aphids. Spray once a week taking turns between solutions. If using these solutions on food plants, be sure to wash them before eating. If using the oil solution, don’t spray on very hot and sunny days as the oil can magnify the sun and possibly harm the plant.
If it's something I can keep an eye on and the infestation is not too bad, I'll usually just spray them off with water.
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