The Q&A Archives: What is Insecticidal Soap?

Question: What is Insecticidal Soap and are there any home recipes for them?

Answer: Soaps have been used to control insects for more than 200 years. How soaps and detergents kill insects is still poorly understood. In most cases, control results from disruption of the cell membranes of the insect. Soaps and detergents may also remove the protective waxes that cover the insect, causing death through excess loss of water. In general, these sprays are effective against most small, soft-bodied arthropods, such as aphids, young scales, whiteflies, psyllids, mealybugs, and spider mites. Insecticidal soaps are considered selective insecticides because of their minimal adverse effects on other organisms. Lady beetles, green lacewings, pollinating bees and most other beneficial insects are not very susceptible to soap sprays.

Several insecticidal soaps are distributed for control of insects and mites. Available under a variety of trade names, the active ingredient of all is potassium salt of fatty acids. Soaps are chemically similar to liquid hand soaps. However, there are many features of commercial insecticidal soap products that distinguish them from the dishwashing liquids or soaps that are sometimes substituted. Insecticidal soaps sold for control of insects are selected to control insects;
are selected to minimize potential plant injury; and are of consistent manufacture.

Some household soaps and detergents also make effective insecticides. However, there is increased risk of plant injury with these products because they are not designed for use on plants. Dry dish soaps and all clothes-washing detergents are too harsh to be used on plants. Identifying safe and effective soap-detergent combinations for insect control requires experimentation.

There are several recipes for homemade insecticial soaps. Here's one:
Buy a liquid soap and not a detergent. Health food stores have liquid soaps, such as Dr. Bronner?s Pure-Castile Soap. Mix 1 to 2 tablespoons liquid soap into one quart of water, then transfer to a spray bottle as needed. This formula can burn leaves, though, so be sure to try it first on a few leaves and wait 3-4 days to see if the product is safe to use on your plants.

Best wishes with your garden!

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