Here’s a really simple recipe for DIY insecticidal soap:
1 tablespoon of soap
2 cups water (1 pint)
Mix thoroughly and add to spray bottle. Spray insects on plants.
Use regular dish soap, not detergent or anything anti-bacterial.
You can also use pure castile soap like the kind from Dr. Bronner which is certified under the USDA National Organic Program.
He also makes a peppermint castile soap. I read that peppermint oil may help repel deer and other large pests but I have not tried it myself. Let me know if you have!
This recipe works best on soft-bodied vegetable patch pests like aphids, thrips, white flies and spider mites. Soaps kill insects by entering the pest’s respiratory system and breaking down internal cell membranes. It is only effective when it is wet, so aim well. After it is dry it will not harm your beneficial insects.
Some insecticidal soap recipes call for adding 1 tablespoon of some kind of oil, either mineral oil or vegetable oil. This will help the mixture adhere to other hard-bodies pests like fleas. But it will also stick to your ladybug beetles so be careful where you are aiming.
Some plants (especially ferns) are sensitive to soaps. You should always test your mixture first on one leaf on your plant. If it is fine the next day, you solution should be OK to use. It is better not to spray your plants in the middle of the day. Full sun (especially on hairy plants) can turn the water droplets into little magnifying glasses which can burn the leaf.
Pests like to hide underneath the leaves. For best results aim up and get under that foliage.
More info on soaps from our pals at the University of Florida IFAS Extension
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