Insecticidal soap is used to control many plant insect pests. Soap has been used for more than 200 years as an insect control. Because insecticidal soap works on direct contact with pests via the disruption of cell membranes when the insect is penetrated with fatty acids, the insect's cells leak their contents causing the insect to dehydrate and die. Insecticidal soap is sprayed on plants until the entire plant is saturated because the insecticidal properties of the soap occurs when the solution is wet. Soaps have a low

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

ian toxicity and are therefore considered safe to be used around children and pets, and may be used in

organic farming Organic farming, also known as ecological farming or biological farming,Labelling, article 30 o''Regulation (EU) 2018/848 of the European Parliament and of the Council of 30 May 2018 on organic production and labelling of organic products and re ...

Composition

Insecticidal soap's active ingredient is most often a potassium salt of fatty acids. Insecticidal soap should be based on long-chain

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, f ...

s (10–18 carbon atoms), because shorter-chain fatty acids tend to be damaging for the plant ( phytotoxicity). Short (8-carbon) fatty-acid chains occur for example in

coconut oil frameless , right , alt = A cracked coconut and a bottle of coconut oil Coconut oil (or coconut butter) is an edible oil derived from the wick, meat, and milk of the coconut palm fruit. Coconut oil is a white solid fat; in warmer climates du ...

and soaps based thereon. "'Green Soap' is a potassium/coconut oil soap ....

hat A hat is a head covering which is worn for various reasons, including protection against weather conditions, ceremonial reasons such as university graduation, religious reasons, safety, or as a fashion accessory. Hats which incorporate mecha ...

has also been shown to be effective, as an unlabeled insecticide, in controlling soft-bodied insects including aphids". Recommended concentrations of insecticidal soap are typically in the range 1–2 percent soap mixed with water. One manufacturer recommends a concentration of 0.06% to 0.25% (pure soap equivalent) for most agricultural applications.; another one recommends concentrations of 0.5 to 1% pure soap equivalent. In the

European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are located primarily in Europe, Europe. The union has a total area of ...

, fatty acid potassium salts are registered and allowed as insecticide at a 2% concentration. Insecticidal soap is most effective if it is dissolved in soft water, since the fatty acids in soap tend to precipitate in

hard water Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bicarbo ...

, thereby reducing the effectivity. Insecticidal soap is sold commercially for aphid control. Labels on these products may not always use the word soap, but they will list "potassium salts of

s" or "potassium laurate" as the active ingredient. Certain types of household soaps (not synthetic

detergent A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are m ...

s, ) are also suitable, but it may be difficult to tell the composition and water content from the label. Potassium-based soaps are typically soft or liquid.

Mechanism of action

The mechanism of action is not exactly understood. Possible mechanisms are: * Soap, which enters via the insect's

trachea The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air- breathing animals with lungs. The trachea extends from t ...

, may disrupt

cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

s, resulting in the cell contents leaking from the damaged cells (

cytolysis Cytolysis, or osmotic lysis, occurs when a cell bursts due to an osmotic imbalance that has caused excess water to diffuse into the cell. Water can enter the cell by diffusion through the cell membrane or through selective membrane channels ...

). * Soap may dissolve the wax layer on the

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

("skin"), which leads to water loss by evaporation. * Soap may block breathing openings or trachea, which leads to suffocation. * Soap may interfere with growth hormones. * Soap may affect insect

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run ...

Affected organisms

Insecticidal soap works best on soft-bodied insects and

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

s such as

aphids Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...

, adelgids, mealybugs,

spider mite Spider mites are members of the Tetranychidae family, which includes about 1,200 species. They are part of the subclass Acari (mites). Spider mites generally live on the undersides of leaves of plants, where they may spin protective silk webs, a ...

thrips Thrips (order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed mostly on plants by puncturing and sucking up the contents, although a few are ...

, jumping plant lice,

scale insect Scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than th ...

s, whiteflies, and sawfly larvae. It can also be used for

caterpillar Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder Sy ...

s and

leafhopper A leafhopper is the common name for any species from the family Cicadellidae. These minute insects, colloquially known as hoppers, are plant feeders that suck plant sap from grass, shrubs, or trees. Their hind legs are modified for jumping, and ...

s, but these large-bodied insects can be more difficult to control with soaps alone. Many pollinators and predatory insects such as lady beetles,

bumblebee A bumblebee (or bumble bee, bumble-bee, or humble-bee) is any of over 250 species in the genus ''Bombus'', part of Apidae, one of the bee families. This genus is the only Extant taxon, extant group in the tribe Bombini, though a few extinct r ...

s, and hoverflies are relatively unaffected. However, soap will kill predatory mites that may help control spider mites. Also, the soft-bodied aphid-eating larvae of lady beetles,

lacewing The insect order Neuroptera, or net-winged insects, includes the lacewings, mantidflies, antlions, and their relatives. The order consists of some 6,000 species. Neuroptera can be grouped together with the Megaloptera and Raphidioptera in the ...

, 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 ''Amblyseius'' is a large genus of predatory mites belonging to the family Phytoseiidae.de Moraes, G. J. (2005)Phytoseiidae Species Listing Biology Catalog, Texas A&M University. Retrieved on August 19, 2010. Many members of this genus feed on ...

andersoni''). Green peach aphids are difficult to control since they reproduce quickly (one adult female can deposit up to four

nymphs A nymph ( grc, νύμφη, nýmphē, el, script=Latn, nímfi, label=Modern Greek; , ) in ancient Greek folklore is a minor female nature deity. Different from Greek goddesses, nymphs are generally regarded as personifications of nature, are ...

per day) because they tend to reside under the leaves and in leaf axils ("leaf armpits"), where they may not be wetted by a soap spray. Manufacturers indeed state that their insecticidal soaps are only suitable for controlling green peach aphids if used in combination with another insecticide, whereas the same soaps can control other aphids on their own. Among green peach aphids that are in contact with a 2% soap solution, around 95% of the adults and 98% of

die within 48 hours. At 0.75% concentration, the mortality rates are reduced to 75% and 90%, respectively. Since 2011, insecticidal soap has also been approved in the United States for use against

powdery mildew Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of ascomycete fungi in the order Erysiphales. Powdery mildew is one of the easier plant diseases to identify, a ...

. In the European pesticide registration, its use as an insecticide is listed for aphids, white fly, and spider mites. It may not be used against

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...

and

moss Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta ('' sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and ...

Use

Insecticidal soap solution will only kill pests on contact; it has no residual action against aphids that arrive after it has dried. Therefore, the infested plants must be thoroughly wetted. Repeated applications may be necessary to adequately control high populations of pests. Soap spray may damage plants, especially at higher concentrations or at temperatures above 32 °C (90 °F). Plant injury may not be apparent until two days after application. Some plant species are particularly sensitive to soap sprays. Highly sensitive plants include: horse chestnut, Japanese maple (''Acer''), ''

Sorbus aucuparia ''Sorbus aucuparia'', commonly called rowan (UK: /ˈrəʊən/, US: /ˈroʊən/) and mountain-ash, is a species of deciduous tree or shrub in the rose family. It is a highly variable species, and botanists have used different definitions of the ...

'' (mountain ash), Cherimoya fruit, '' Lamprocapnos'' (bleeding heart), and sweet pea. Other sensitive plants are, for example: '' Portulaca'', some tomato varieties, ''

Crataegus ''Crataegus'' (), commonly called hawthorn, quickthorn, thornapple, Voss, E. G. 1985. ''Michigan Flora: A guide to the identification and occurrence of the native and naturalized seed-plants of the state. Part II: Dicots (Saururaceae–Cornacea ...

'' (hawthorn),

cherries A cherry is the fruit of many plants of the genus '' Prunus'', and is a fleshy drupe (stone fruit). Commercial cherries are obtained from cultivars of several species, such as the sweet ''Prunus avium'' and the sour ''Prunus cerasus''. The ...

plum A plum is a fruit of some species in ''Prunus'' subg. ''Prunus'.'' Dried plums are called prunes. History Plums may have been one of the first fruits domesticated by humans. Three of the most abundantly cultivated species are not found ...

, ''

Adiantum ''Adiantum'' (), the maidenhair fern, is a genus of about 250 species of ferns in the subfamily Vittarioideae of the family Pteridaceae, though some researchers place it in its own family, Adiantaceae. The genus name comes from Greek, meaning "un ...

'' (maidenhair fern), ''

Euphorbia milii ''Euphorbia milii'', the crown of thorns, Christ plant, or Christ thorn, is a species of flowering plant in the spurge family Euphorbiaceae, native to Madagascar. The species name commemorates Baron Milius, once Governor of Réunion, who introdu ...

'' (crown of thorns), ''

Lantana camara ''Lantana camara'' (common lantana) is a species of flowering plant within the verbena family ( Verbenaceae), native to the American tropics. It is a very adaptable species, which can inhabit a wide variety of ecosystems; once it has been introdu ...

'', '' Tropaeolum'' (nasturtium), ''

Gardenia jasminoides ''Gardenia jasminoides'', commonly known as gardenia, is an evergreen flowering plant in the coffee family Rubiaceae. It is native to parts of South-East Asia. Wild plants range from 30 centimetres to 3 metres (about 1 to 10 feet) in height. Th ...

'', ''

Lilium longiflorum ''Lilium longiflorum'' (Japanese: テッポウユリ, ''Teppōyuri''), often called the Easter lily, is a plant endemic to both Taiwan and Ryukyu Islands (Japan). '' Lilium formosanum'', a closely related species from Taiwan, has been treated as ...

'' (Easter lily).

Conifer Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All ext ...

s under (drought) stress or with tender new growth are sensitive as well. Damage may occur as yellow or brown spotting on the leaves, burned tips, or leaf scorch. Plants under

drought A drought is defined as drier than normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D. Jiang, A. Khan, W. Pokam Mba, D. Rosenfeld, J. Tierney, an ...

stress, young transplants, unrooted

cutting Cutting is the separation or opening of a physical object, into two or more portions, through the application of an acutely directed force. Implements commonly used for wikt:cut, cutting are the knife and saw, or in medicine and science the scal ...

s and plants with soft young growth tend to be more sensitive. Sensitivity may be tested on a small portion of a plant or plot before a full-scale application. One manufacturer recommends that applications are done with 7- to 14-day intervals, with a maximum of three applications, as repeated applications may aggravate phytotoxicity. In addition, water conditioning agents can increase phytotoxicity. Thanks to its low mammalian toxicity, application of insecticidal soap is typically allowed up to the day of harvest.

References

{{reflist, refs= "Soaps" and Detergents: Should They Be Used on Roses?
R.A. Cloyd, American Rose Society (2018).
M.L. Flint, University of California Davis, July 2013.
W.S. Cranshaw, University of Colorado. March 2008.
J. D. Ubl, Clemson University, July 2009. Insecticidal Soaps - Modes of Action
(video). L.L. Keeley (20 Aug 2013). Toxicity of biopesticides to green apple aphid, predatory insects and mite in an apple-tree orchard
L. Raudonis et al., Zemdirbyste-Agriculture, vol. 97, No. 1 (2010), p. 49–54. Pesticide product label for Super insecticidal soap concentrate
US Environmental protection agency, July 2011. According to the ''Super insecticidal soap concentrate label'' above: 0.5 pint of a 25% concentrate per 25 gallons = 0.06%. Toxicity effects of an insecticidal soap on the green peach aphid
{{webarchive, url=https://web.archive.org/web/20150402192822/https://www.mysciencework.com/publication/file/1970822/toxicity-effects-of-an-insecticidal-soap-on-the-green-peach-aphid-homoptera-aphididae , date=2015-04-02 . E. Tremblay et al., Phytoprotection 90: 35-39 (2009). Pesticide product label for M-Pede insecticide miticide fungicide
US Environmental protection agency, July 2011. Fatty acids C7 to C20
{{webarchive, url=https://web.archive.org/web/20150419172351/http://ec.europa.eu/sanco_pesticides/public/index.cfm?event=activesubstance.detail&language=NL&selectedID=1322 , date=2015-04-19 . EU-database voor pesticides. Review report for the active substance Fatty Acids C7 to C20
{{webarchive, url=https://web.archive.org/web/20150419172318/http://ec.europa.eu/sanco_pesticides/public/index.cfm?event=activesubstance.ViewReview&id=746 , date=2015-04-19 . Europese Commissie (2013). Insecticides Sustainable agriculture

Composition

Mechanism of action

Affected organisms

Use

See also

References