Several threads mention people killing or injuring their plants with the stuff, especially homemade, or when applied when its too hot and dry. The stuff can remove the natural wax coating from leaves, causing them to dry out and burn. Read instructions carefully and test it out on one or two plants first.

Insecticidal soap is considered "natural" and organic. Insecticidal soap isn't harmful to beneficial insects...or so I've read.

I believe the Safer company was the 1st to market insecticidal soap. It's best for killing soft bodied insects such as aphids and mealy bug.

There are several commercial brands available on the market - Safer's is one. Or you can make your own using 1 T of liquid soap in 1 gallon of water.

What causes people problems with it is making the mix way too strong or misunderstanding how to use it. The keys to success with it is (1) early morning or late evening spray only - NEVER in direct sun or heat of the day, and (2) do not drench the plant, just lightly spritz it focusing on hitting the insect pests directly. Some then rinse the plant 1/2 to 1 hour later.

A search using your post title pulls up over 100 discussions about it complete with many brand names and notes on use and pest effectiveness. Lots of good reading. ;)

Dave

"natural" and "organic" doesn't mean it still doesn't kill beneficial insects.

Take the time to learn that there is not a "cure all" for every pest at every stage of it's life cycle. Some won't work if it's going to rain. Some don't work well if it's too hot, etc.

Pest management is complex, if you wish to use chemical products, do so responsibly which goes further than reading the label. If you want to learn, a good place to start is here:

Integrated Pest Management
This lecture is presented in two parts. Each part is 90-minutes in length. Recorded in Sacramento County in California's Sacramento Valley, this lecture is by Mary Louise Flint, Ph.D., Director, IPM Education and Publications, UC Statewide IPM Project and Extension Entomologist & Cooperative Extension Specialist.

Education:
B.S. Plant Science, University of California, Davis
Ph.D. Entomology, University of California, Berkeley

Appointment:
100% Cooperative Extension

Research Interests:
Integrated pest management of landscape, agricultural and garden pests; biological control of arthropod pests; alternatives to pesticides; adoption of alternative practices by practitioners; innovative delivery of pest management information.

Topics discussed in the Integrated Pest Management Lecture:

* IPM references and resources
* Preventing pest problems
* Natural common enemies
* Making less toxic pesticide choices
* Controlling aphids, scales, caterpillars, coddling moths, tree borers, snails and slugs, and lawn insects.

You can watch the programs now online:

Just make sure you have Real Player installed or download it free.

Integrated Pest Management Part1 90 minutes

Integrated Pest Management Part 2 90 minutes

You'll want to bookmark the following link to Professor Flint's Lab Research on:
Controlling Pests in Gardens and Landscapes: Vegetables and Melons

I promise you'll learn one or two things to put in your gardening bag of pest management arsenals.

;)

"natural" and "organic" doesn't mean it still doesn't kill beneficial insects."

Violet, no need to get yourself in a tizzy. I didn't say it did. Insecticidal soap, such as Safer's is accepted for use by organic growers. The label on the Safer bottle says that it does not harm beneficial insects. Read it for yourself.

Here is a link that might be useful: Safer's Insecticidal Soap

Yes, it's natural and very effective on soft body insects. Personally, I prefer not to use any homemade soap mix on my plants. These insecticidal soaps have some salts that adhere to the body of the insects with the help of the soap, and dehydrate them. The one I buy here can be used safely up to the date of harvest on all edibles. Always of course, follow carefully the instructions.

To answer the original question, insecticidal soaps are generally fatty acids from petroleum products, but in some cases it's the fatty acids from plants. Either way they work by removing the protective coating from soft bodied insects that keeps moisture inside them so they dry out and die.

Commercial insecticidal soaps work very well and are formulated to not cause damage to plants. Various dish 'soaps' and other homemade versions usually do not work as well nor are they refined for use on plants so the risk of damaging the plant is much greater.

Regardless of whether you use a commercial product or make your own their use should be avoided in the heat of day.

The soaps are generally effective on soft bodied insects like aphids, mealie bugs, white fly, thrips etc. They are only marginally effective on caterpillars and generally ineffective on hard bodied pests like beetles.

Insecticidal soaps are also excellent to use as an emulsifying agent (aka spreader stickers) in that it helps 'stick' other products to plants that would otherwise wash off. A common anti fungal 'recipe', as an example, calls for 1 tablespoon baking soda, 1 teaspoon insecticidal soap to 1 gallon of water. The soap helps the baking soda stick to the plant surface and kill the fungus.