Insecticidal Soaps: An effective and eco-friendly pest control method for sustainable agriculture
Insecticidal soaps, also known as potassium salts of fatty acids, are bio pesticides used as insecticides, herbicides, fungicides, and algaecides. They are produced by combining potassium hydroxide with fatty acids derived from animal fats and plant oils, such as palm, coconut, olive, castor, and cottonseed. They work through various mechanisms, offering farmers safe alternatives to chemical pesticides.
Description
Presentation
Soap was first discovered and used by the Chinese as a pesticide in 1101 A.D and It has also been used as an insecticide in Europe since 1787. Before 1900, fish or whale oil soaps were the most commonly used insecticidal soaps. Although the first pesticide product containing soap salts was registered for use in 1947 (USEPA, 1992). [1]
Insecticidal soaps are biodegradable and specifically designed for pest control and are widely used in organic farming. The solution is sprayed directly on pests, killing them upon contact. It is less toxic for humans and short lived in the environment and does not leave harmful residues on crops. [2]
Composition and molecular structure for Potassium salt of long chain fatty acids
Soap is technically sodium or potassium salt of a fatty acid. Soap is produced as a result of the chemical reaction called ‘saponification. This takes place when fatty acids (plant oils, butters or animal fats) are emulsified with a sodium or potassium hydroxide solution. For insecticidal soap, the active ingredient is most often a potassium salt of long chain fatty acids.(Ahmad et al., 2020)
How to make homemade insecticidal soap ?
Traditional DIY Insecticidal Soap: An effective and Eco-Friendly solution, simply mix and pour into a spray bottle for easy application:
The ingredients:
- 2.5 tablespoons (37 ml) pure liquid soap (not detergent), advisably castile soap.
- 1 gallon (3.8 L) warm water (distilled or tap, but not hard)
- 2.5 tablespoons (37 ml) vegetable oil
Procedure to follow when making insecticidal soaps
To make a homemade insecticidal soap:
- Start by measuring 2.5 tablespoons (37 ml) of vegetable oil and 2.5 tablespoons (37 ml) of pure liquid soap.
- In a large container or directly in a spray bottle, add 1 gallon (3.8 L) of warm water, which helps dissolve the ingredients.
- Pour the measured oil and soap into the water and stir gently to combine, avoiding excessive bubbles. If using a container, transfer the mixture carefully into a clean spray bottle.
- Before each use, shake the spray bottle to ensure the oil and soap are evenly mixed, as they may separate over time. [3]
Video on How to make homemade insecticidal soap
Insecticidal soap products available on the market
Safer leads the market in insecticidal soaps with its OMRI-listed Insect Killing Soap, popular for organic gardening. Garden Safe and Espoma's Earth-tone line also offer trusted, eco-friendly options for natural pest control, while Natria by Bayer provides effective solutions tailored to home gardeners seeking safe, sustainable pest management. [4]
The cost of purchasing insecticidal soap
Insecticidal soap products vary in price depending on the brand and packaging size. However the price range for insecticidal soap products from leading brands generally falls between €6.50 and €46 for 709 ml to 1 liters.
Safer Brand Insect Killing Soap, ranges from about €11 for a 16-ounce (473 ml) concentrate (makes up to 6 gallons) to around €46 for larger ready-to-use versions with multiple spray bottles and Garden Safe Insecticidal Soap, priced at approximately €6.50 for a 24-ounce (710 ml) ready-to-use bottle (Prices are converted from Dollar to Euro) [5]
On the other hand, Making insecticidal soap at home can be affordable and simple with basic household ingredients. When compared to commercial options, homemade insecticidal soap offers a cost-effective and organic pest control method for gardeners looking to reduce expenses and avoid synthetic chemicals.
Mode of action
The mode of action of soaps is still not well-understood although there are four ways by which soaps may kill insect and mite pests.
- Soaps may penetrate through the fatty acids present in the insect’s outer covering (cuticle) thus dissolving or disrupting cell membranes. This impairs cell integrity causing cells to leak and collapse, destroying respiratory functions, and resulting in dehydration and death of the insect or mite pests.
- Soaps may block the spiracles (breathing pores), interfering with respiration thus leading to suffocation.
- Soaps interfere with insect growth regulators, interfering with cellular metabolism and the production of growth hormones during metamorphosis.
- Soaps may uncouple oxidative phosphorylation or inhibit the production of adenosine triphosphate (ATP), which reduces energy production, (“Insecticidal Soap,” 2024; Makenzie, 2024).
A guiding video of the mechanism of insecticidal soap on insects
How to use insecticidal soap
Application
Spray directly the infected plant, it is important to spray both the top surface and, especially, the underside of the leaves as many of the pests will be found Demon Maxthere’’. Because of the relatively short residual action and the fact that the insects must be in contact with the soap to be effective, repeat applications may be necessary every 4- to 7-days (follow the label directions) until the pests are eliminated. Avoid excessive applications as leaf damage may accumulate with repeated exposure. Always follow the directions on the label.
The quality of the water you are using should be considered when using insecticidal soaps. Hard water reduces the effectiveness of the insecticidal soap. It is important to use the purest water possible. You can determine if your tap water is compatible by mixing the recommended concentration of soap that you want to use with the appropriate amount of water in a glass jar. Agitate and let the mixture stand for 15 minutes. If the mix remains uniform and milky, the water quality is fine for the spray. If there is scum on the surface, you should use distilled or bottled water, (Cranshaw, n.d.; Features, 2013).
Frequency: Reapply every 7-10 days, or as needed, to maintain control over pest populations.
Reapplying insecticidal soap is necessary to maintain its effectiveness against pest infestations. Typically, it should be reapplied every 7–10 days, especially during severe infestations. This frequency ensures that any newly hatched pests are targeted before they can reproduce. It’s important to follow label instructions, as excessive use can harm plants or reduce the effectiveness of the treatment. Applying it early in the morning or late in the evening is recommended to prevent potential plant stress from sunlight exposure.
Where insecticidal soap is used?
Insecticidal soaps can be used in vegetable gardens, orchards, greenhouses, and even on houseplants. They are particularly effective on crops like tomatoes, cucumbers, leafy greens, and fruit trees.
Use and targeted pest
Insecticidal soap can be used as an insecticide, fungicides, algaecide and herbicide for example M-Pede Fungicide used as biological fungicide, specifically in controlling powdery mildew. In the United States, for one, insecticide soap has been officially approved for use as a fungicide, specifically in powdery mildew on vegetables and roses (Hodgson (1954-2022), 2018).
Insecticidal soap works best on soft-bodied insects and other arthropods such as:
It can also be used for caterpillars and leafhoppers, but these large-bodied insects can be more difficult to control with soaps alone. (Cranshaw,W.S. (2008; “Insecticidal Soap,” 2024). [6]
When to use it
Timing: Use insecticidal soaps during the early morning or late afternoon to avoid direct sunlight, which can cause plant damage (phytotoxicity).
Insecticidal soap is generally effective only when it remains wet on the plant surface. While it’s wet, the soap targets soft-bodied insects by penetrating their cell membranes and dehydrating them, which leads to their elimination. Once the soap dries, its insecticidal properties are no longer active and it becomes far less likely to impact insects. This is why reapplication is sometimes recommended after rain, as the product may wash away and reduce effectiveness if it hasn’t had time to work while wet. For those concerned about non-target insects on the ground, dried insecticidal soap residue is less harmful and generally safe, as it loses its ability to affect insect cell membranes once it’s no longer in liquid form. [7] If it rains soon after applying insecticidal soap, the spray could potentially wash off and reach the ground. Insecticidal soaps are generally designed to have minimal impact on non-target organisms, and they degrade quickly without residual action once dried. [8]
Pest Life cycle: Best used when pest populations are still small. Monitor plants regularly for early signs of infestation.
Advantages (For the farmer and environment)
Environmentally Friendly: Insecticidal soaps are biodegradable and have minimal impact on non-target organisms, making them safe for beneficial insects like ladybugs and pollinators.
Organic Certification: Approved for use in certified organic farming.
Safe to Use: Non-toxic to humans, animals, and plants when used properly.
Cost-Effective: A cheaper alternative to synthetic pesticides,(Ryan, 2013).
The limits (For the farmer and environment)
Limited Spectrum: Only effective against soft-bodied insects and requires direct contact, so it’s not useful for hard-shelled pests like beetles.
It may kill predatory mites. Toxic to aquatic invertebrates, and slightly toxic to cold-water and warm-water fish.
Phytotoxicity: Overuse or improper application can cause plant damage. Potential to cause plant injury — phytotoxicity. Hairy leaf plants may hold the soap on their surfaces longer, resulting in a burn, (Ryan, 2013).
Weather sensitivity: Rain can wash away the soap, reducing effectiveness.
Detrimental to some beneficial organisms. Soap will kill predatory mites that may help control spider mites. Also, the soft-bodied aphid-eating larvae of lady beetles, lacewing, and hoverflies may be affected negatively. According to one study a single soap application killed about 15% of lacewing and lady-beetle larvae, and about 65% of predatory mites (Amblyseius andersoni). Toxic to aquatic invertebrates, and slightly toxic to cold-water and warm-water fish. [9]
How to get insecticidal soap
Insecticidal soaps are widely available at garden centers, agricultural supply stores, and online retailers. Brands like Safer and Bonide offer organic-certified insecticidal soap products.
Some relevant links to purchase different brands of insecticidal soap
- https://vegetalbioplant.com/en/protection-stress/61-potassium-soap-premium.html?srsltid=AfmBOoowHSMVKc7dMFz_uqtWQYGQ4HlEykXxJDdueAfzHIUPoHYmZQjv
- Insecticidal Soap RTU - Bonide
- https://bioadvanced.com/natria-insecticidal-soap-ready-to-use-24-oz.html
- https://bowoodfarms.com/products/insecticidal-soap-spray-16oz-con
Current regulation of insecticidal soaps
In the EU, insecticidal soaps are regulated to ensure they are safe and effective, especially on edible crops. Overseen by the European Food Safety Authority (EFSA), these soaps, recognized as low-risk due to their natural composition, must meet strict pesticide standards to be approved. EFSA requires extensive testing to confirm that these products effectively target pests without harming non-target species, human health, or the environment. Once approved, insecticidal soaps are monitored continuously, aligning with the EU’s sustainable agriculture goals, including Integrated Pest Management (IPM), which encourages reduced chemical use and safer pest control methods.
- Approved for use in EU organic agriculture under EU Regulation (EC) No 889/2008
- In the European pesticide registration, its use as an insecticide as listed for aphids, white fly, and spider mites
Since 2011, insecticidal soap has also been approved in the United States for use against powdery mildew, (farmonaut, n.d.; Hodgson (1954-2022), 2018; How Pesticides Are Regulated in the EU - EFSA and the Assessment of Active Substances | EFSA, 2018; Insecticidal Soaps | Agricultural Marketing Service, n.d.; Pesticide Evaluations, n.d.; Sustainable Use of Pesticides - European Commission, n.d.). [10]
Example of experimental test done on insecticidal soap as a fungicide.
Use of organic olive soap in Squash cultivation to control Powdery Mildew:
Cultural Practices
The application of organic olive soap not only serves as a fungicide but also complements sustainable agricultural practices by reducing the need for conventional chemical treatments. Used to manage powdery mildew, a common fungal pathogen in squash and other vegetable crops, these soaps disrupt fungal cell membranes, curbing the pathogen’s spread on plant surfaces. When combined with other cultural practices, such as ensuring proper air circulation and reducing excess leaf moisture, the application of organic olive soap can significantly improve the effectiveness of powdery mildew control strategies.
Specific efficacy against Powdery Mildew
In a controlled greenhouse study, organic olive soap applications in squash crops led to a noticeable reduction in powdery mildew infections. The study explored various application regimens, finding that applying the soap preventively, or at the first signs of mildew, offered the best results. Regular treatments, applied every 7–10 days, helped keep the disease under control, especially when integrated with preventive measures like reducing dense plant growth and removing infected leaves. These combined efforts help create an environment less conducive to mildew proliferation, offering a holistic solution to managing fungal infections.
Greenhouse experiment conditions
The research was conducted under the following experimental conditions:Spacing and Application: Squash plants were sprayed with organic olive soap solutions at regular intervals, while untreated control plants served as a comparison.
Application Frequency: For best efficacy, treatments were reapplied at intervals, ensuring the active ingredients reached the leaves and stems most vulnerable to powdery mildew.
This study highlights the role of organic olive soap in sustainable pest management systems, particularly valuable in Integrated Pest Management (IPM). The minimal environmental footprint of these soaps makes them ideal for organic farming and eco-conscious agriculture, supporting the health of beneficial organisms while targeting pathogenic fungi.(Frem et al., 2022).
Testimonials from farmers
Review from farmer on the use of SAFER Insecticidal soap products
References
http://npic.orst.edu/factsheets/archive/psfatech.pdf
A Short History of Pest Management. (n.d.). Retrieved 1 November 2024, from https://extension.psu.edu/a-short-history-of-pest-management
Fundamentals of Using Soaps as Insecticides | Extension Entomology. (n.d.). Retrieved 1 November 2024, from https://blogs.k-state.edu/kansasbugs/2020/06/12/fundamentals-of-using-soaps-as-insecticides/
Ahmad, Z., Noor, S., Ahmad, M., & Rashid, K. (2020). Optimum Composition of Developed Additive Based Insect Repellent Paint. https://doi.org/10.21203/rs.3.rs-98595/v1
Bentley, R. (2023, June 19). 5 Best Insecticidal Soaps (2024 Guide). This Old House. https://www.thisoldhouse.com/pest-control/89645/best-insecticidal-soap
Cloyd, R. A. (2023). Horticultural Entomology and Plant Protection Specialist.
Cranshaw, W. (n.d.). Insect Control: Soaps and Detergents.
farmonaut. (n.d.). EU Agricultural Policy Update: EFSA’s 2024 Procurement Process for Food Safety and Sustainable Farming. Retrieved November 3, 2024, from https://farmonaut.com/europe/eu-agricultural-policy-update-efsas-2024-procurement-process-for-food-safety-and-sustainable-farming/
Features, A. G. last updated in. (2013, January 11). A Complete Guide To Homemade Insecticidal Soap. Gardeningknowhow. https://www.gardeningknowhow.com/plant-problems/pests/pesticides/homemade-soap-spray.htm
Frem, M., Nigro, F., Medawar, S., & Moujabber, M. E. (2022). Biological Approaches Promise Innovative and Sustainable Management of Powdery Mildew in Lebanese Squash. Sustainability, 14(5), Article 5. https://doi.org/10.3390/su14052811
Hodgson (1954-2022), L. (2018, April 12). Insecticidal Soap Is Also a Fungicide. Laidback Gardener. https://laidbackgardener.blog/2018/04/12/insecticidal-soap-is-also-a-fungicide/
How pesticides are regulated in the EU - EFSA and the assessment of active substances | EFSA. (2018, April 24). https://www.efsa.europa.eu/en/corporate/pub/pesticides-ebook-180424
https://en.wikipedia.org/w/index.php?title=Insecticidal_soap&oldid=1229181943
Insecticidal Soaps | Agricultural Marketing Service. (n.d.). Retrieved November 3, 2024, from https://www.ams.usda.gov/rules-regulations/organic/petitioned-substances/insecticidal-soaps
Makenzie. (2024, September 5). “Soaps” and Detergents: Should They Be Used on Roses? American Rose Society. https://rose.org/soaps-and-detergents-should-they-be-used-on-roses/
Pesticide evaluations: Regulations and guidance | EFSA. (n.d.). Retrieved November 3, 2024, from https://www.efsa.europa.eu/en/applications/pesticides/regulationsandguidance
Ryan, J. (2013, August 5). Insecticidal soap. Farmer’s Weekly. https://www.farmersweekly.co.za/crops/field-crops/insecticidal-soap/
Sustainable use of pesticides—European Commission. (n.d.). Retrieved November 3, 2024, from https://food.ec.europa.eu/plants/pesticides/sustainable-use-pesticides_en
Annexes
