PlantLife Online

Did you know you can control soft body insects like aphids and mites with a simple solution of common dish soap and water? Soaps have been used for insect control for around 200 hundred years and recently have become more popular among homeowners. The soap solution should be applied to the upper and lower surfaces of the leaves, the soapy solution as no residual effectiveness and should applied directly on the insects. Repeat applications over 7-10 days may be needed for complete insect control. Home made soap solutions are effective against most small, soft-bodied arthropods, such as aphids, young scales, whiteflies, psyllids, mealybugs, and spider mites. Larger insects, such as caterpillars, sawflies and beetle larvae, generally are immune to soap sprays. However, a few large insects, including boxelder bugs and Japanese beetles, are susceptible.
A few drops (1% solution=1-2 tbsp per gallon, 2 tsp per liter) of common dish soap in each gallon of water can be effective and cheaper than manufactured insecticides. However too high of concentration of soap, heavy duty detergents and anti-bacterial soaps my cause plant injury. To avoid damaging your plants try the solution on a few leaves a couple days before applying all over the plant.