Answer: Insecticidal soaps are made from fatty acids derived from plants and are considered the least toxic, most effective way to kill soft bodied insects such as aphids. All soaps are long chain fatty acids, but not all soaps have insecticidal properties. Insecticidal soaps are specifically formulated to have high insect-killing properties, while being safe for most plant species.
Insecticidal soaps kill susceptible insects by washing away the protective coating on the surface of the insect and by disrupting normal membrane functions inside the insect. The insects must come into direct contact with the spray droplets for the material to be effective. Good coverage is essential. The soaps have no residual activity toward insects, but repeated applications may have damaging effects on some types of plants.
Safer's Insecticidal Soap has been on the market a very long time; Bayer has an insecticidal soap product, as do many other manufacturers. I always choose the brand that is on sale when I need it!
Hope this information helps clarify things for you.
Q&A Library Searching Tips