Homemade Insecticidial Soap
Answered by: Conrad Richter
Question from: Elizabeth Duggan
Posted on: May 31, 2001

Thank you for "being there."

Do you know of a simple, do-it-yourself formula for insecticidial soap? I live in a small town in Mexico, and commercial preperations like this are hard to find. I also have white flies.

The commercial products made by Safer’s and others differ from ordinary soaps in that the fatty acid salts are made with potassium instead of sodium. Plants will suffer if sodium levels are too high, whereas potassium is one of the three major nutrients for plants. In addition, some commercial products contain additives such as the botanical insecticide pyrethrum that improve knockdown rates.

Still, it is possible to make a very effective homemade spray using liquid soap. Make sure that the soap is in fact a soap and not a detergent which is toxic to plants. The dilution rate (with water) should be about 1 part soap to 20 to 50 parts of water. Test the mixture on a few plants to make sure that the concentration is not too strong to cause wilting and burning of the leaves. Any damage will be visible within a few hours of application. Adjust the dilution rate accordingly.

Insecticidal soap at high concentrations acts as a herbicide (which is how we control weeds in our greenhouses which is why you need to test and adjust your soap spray concentration.

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