Composition and Mechanism of Action
– Insecticidal soaps are potassium salts of fatty acids.
– Long-chain fatty acids are preferred to avoid plant damage.
– Short-chain fatty acids found in coconut oil can be used to make insecticidal soaps.
– Green Soap, a potassium/coconut oil soap, is effective against soft-bodied insects.
– Recommended concentrations range from 12% soap mixed with water to 0.5-1% pure soap equivalent.
– The exact mechanism of action is not fully understood, but possible mechanisms include disruption of cell membranes, dissolving the wax layer on the insect’s skin, suffocation, interfering with growth hormones, and affecting insect metabolism.
Affected Organisms
– Insecticidal soap works best on soft-bodied insects and arthropods like aphids, adelgids, mealybugs, spider mites, and thrips.
– It can also be effective against caterpillars and leafhoppers.
– Predatory insects like lady beetles, bumblebees, and hoverflies are relatively unaffected.
– Predatory mites may be killed by soap.
– Green peach aphids are challenging to control with insecticidal soap alone.
Use
– Insecticidal soap only kills pests on contact and has no residual action.
– Infested plants must be thoroughly wetted with the soap solution.
– Repeated applications may be necessary for high pest populations.
– Soap spray can damage plants, especially at higher concentrations or high temperatures.
– Certain plants, such as conifers under stress or with tender new growth, are more sensitive to soap spray.
References
– Cranshaw, W.S. (2008). Insect Control: Soaps and Detergents: Fact Sheet.
– Oregon State University, National Pesticide Information Centre (NPIC) (2001). Potassium Salts of Fatty Acids: General Fact Sheet.
– Cloyd, Raymond A. (2018). Soaps and Detergents: Should They Be Used on Roses?.
– Pesticide product label for Super insecticidal soap concentrate. US Environmental protection agency, July 2011.
– Pesticide product label for M-Pede insecticide miticide fungicide. US Environmental protection agency, July 2011.
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– May contain unverified or inaccurate information.
– Not recommended for academic or research purposes. Source: https://en.wikipedia.org/wiki/Insecticidal_soap
