Do you prefer organic pest control? Have you seen lots of homemade pest remedies on Facebook or gardening websites that you wonder if you should try? Then you’ve probably heard of insecticidal soap! What you may not know is that:
- Many things we think of as “soaps” aren’t really soaps
- Not all soaps are effective as insect killers
- Many soaps may damage or even kill your plants rather than your pests!
So what ARE insecticidal soaps?
Insecticidal soaps are soap products registered as insecticides. According to Raymond Cloyd, Extension Entomologist, Kansas State University, they are “‘reduced risk’ insecticides…used in certain situations because they leave minimal residues, are less toxic to humans, and are short-lived in the environment because they degrade rapidly.” He notes that “Soap is a general term for the salts of fatty acids.”
The Environmental Protection Agency only registers potassium salts of fatty acids as active ingredients of insecticidal soaps. Why does this matter? Other salts and other fatty acids in soaps aren’t necessarily effective as insecticides—and may be harmful to plants!
Should you use an insecticidal soap for pest control?
First, identify your pest! Not all insects are pests and not all pests are controlled with insecticidal soaps. Then decide if your plants will benefit from using insecticidal soap:
- Will the affected plants tolerate insecticidal soap? Read the label to be sure the product is registered for use on the garden plants that pests are threatening.
-
Insecticidal soap label. - Do your plants need intervention—how much pest damage can you—and your plants—tolerate?
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Adult Ladybug eating an aphid. Do you need an insecticide?
Commercially produced insecticidal soap sprays can effectively kill “soft-bodied” pests they come in contact with, such as:
- Aphids,
- Leafhoppers,
- Mealybugs,
- Mites,
- Scales,
- Thrips, and
- Whiteflies
-
Thrip damage on onions. Is this sufficient to warrant use of an insecticide? 
Whiteflies: Does this infestation justify using an insecticide?
Insecticidal soaps are most effective on the early stages of pest development—such as larvae—and safest when applied only to plants listed on the product label when those plants are not under too much stress. In other words, use insecticidal soap when pests first start to appear in sufficient numbers to become a threat to your plants.
Insecticidal soaps can’t:
- Control soft-bodied insects after the spray dries on the plant—only spray when you can see the pests!
- Control “hard-bodied” insects, such as beetles.
- Distinguish between beneficial insects and pests!
Are all insecticidal soaps organic?
Check the Organic Materials Review Institute (OMRI) list for registered organic pesticides. Many pesticides that contain potassium salts of fatty acids contain other active ingredients that are not organic.
What about those recipes for insecticidal soap?
Many “soaps” you have in your home are detergents, not soaps! These cleaning products may kill your plants rather than your pests. Even those soap products on your shelf that might have some insecticidal properties may damage your plants or may not be as effective as products registered for garden use. If asked, the makers of popular soap products will emphasize like we do—read the label! If the product isn’t registered for garden use, don’t use it!
Article by Buncombe County Extension Master GardenerSM Volunteers
For more information:
Raymond Cloyd, “Fundamentals of Using Soaps as Insecticides”:
https://blogs.k-state.edu/kansasbugs/2020/06/12/fundamentals-of-using-soaps-as-insecticides/
OMRI Products List: https://www.omri.org/omri-lists/download
How to choose a pesticide: http://npic.orst.edu/pest/select.html
Discussion of pest tolerance: https://extension.entm.purdue.edu/radicalbugs/default.php?page=decision_making
Organic gardening: https://content.ces.ncsu.edu/extension-gardener-handbook/17-organic-gardening#insects