Pesticides that work on aphids include insecticidal soaps and oils, pyrethrins, malathion, acephate and permethrin. Among these, the least effective are soaps and oils; however, they are the best choice for aphid control, considering that they are far less toxic than the alternatives.
Insecticidal oils may be petroleum-based or derived from plant oils. They act by smothering the aphids, as do soap-based pesticides. Soaps and oils only act on aphids on the day of application. On the other hand, chemicals, such as malathion, acephate and permethrin, are active for up to 15 days following application; however, due to their toxicity, these chemicals are not good for use on food crops. Pyrethrins are not as toxic, but they provide moderate action against aphids. For better results where food crops are involved, a mixture of pyrethrins and insecticidal soaps is acceptable.