What is Insecticidal Soap?

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Suzanne Wainwright-Evans

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Not only do insecticidal soaps work on pesky insects, they also kill spider mites.

One item every gardener should have in his or her arsenal is insecticidal soap. The product is great because it’ll kill almost any pest insect on contact, it’s safe to handle and economical. It also has minimal impact on beneficial insects and the environment.

“Hey, soap is soap,” you might be thinking. But it really isn’t. In general, soap is a substance made by combining a fat with either an alkali, like sodium (as with hard soap), or potassium hydroxide (soft soap). While there are lots of fatty acids out there used to make soap, only certain ones have insecticidal properties.

So that said, and contrary to any rumors you may have heard, you can’t just use ordinary kitchen soap to control an insect problem in the garden. In fact, some household soaps can actually kill plants. (And these soaps are NOT organic!)

One fundamentally important property of horticultural soaps has to do with how many carbons are attached to them. Soaps with lots of carbons, for example, are long-chain fatty acids and have insecticidal properties. On the other hand, when carbons are removed from the soap, you end up with short-chain fatty acids, which tend to have herbicidal properties. (Herbicides are what you use to kill weeds.)

This is why it’s so important to use store-bought insecticidal soaps and not just any kitchen or bath soap for gardening situations. Do you know if your dish soap is a short- or long-chain fatty acid? Is it an insecticide or an herbicide? Do you know if it’ll burn your plant? These are very serious questions!

Facts

Insecticidal soaps are one of the least expensive pesticides on the market.
There are also organic insecticidal soaps out there. You need to look for the OMRI (Organic Materials Review Institute) logo or other certifying agency logo on the label.

Tips

Insecticidal soaps only kill if they come in contact with the pest. So know where your pest is located on your plant before you spray. (Often it’s on the undersides of leaves.)

Definitions

Herbicide: A product used to kill unwanted plants (weeds).

Faqs

Q: If I mix insecticidal soap at a higher rate will it kill pests better?
A: No. This can damage your plant or even kill it. Stronger is not better! Always follow label instructions!

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Articles

How to Use Insecticidal Soap
Insecticidal soap is a great tool for any gardener’s plant management program. Knowing how to use this product – and understanding its limitations – is key to successful pest control.
Fighting Pests and Diseases in Your Natural Garden
When you’ve got a natural garden, it just makes sense to garden naturally. So put aside those synthetic controls. Good gardening practices, coupled with keen scouting and organic pest and disease control, should be enough when fighting garden pests – and can keep your landscape lush and lovely.
Integrated Pest Management: Part 1
Want to keep the pests away without using chemicals? Practice integrated pest management! Learn the basics of this important method – from what IPM is to how it helps prevent pest problems.

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