{{Short description|Spray used to kill plant pests}} '''Insecticidal soap''' is used to control many plant insect pests. Soap has been used for more than 200 years as an insect control.<ref name=":1">{{Cite web|url=https://extension.colostate.edu/topic-areas/insects/insect-control-soaps-and-detergents-5-547/|title=Insect Control: Soaps and Detergents: Fact Sheet|last=Cranshaw|first=W.S.|date=2008|website=Colorado State University: Extension|access-date=4 December 2019}}</ref> 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.<ref>{{Cite web|url=http://npic.orst.edu/factsheets/psfagen.pdf|title=Potassium Salts of Fatty Acids: General Fact Sheet|last=Oregon State University|first=National Pesticide Information Centre (NPIC)|date=2001|website=|access-date=4 December 2019}}</ref> 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.<ref name=":0">{{Cite web|url=https://www.rose.org/single-post/2018/03/20/%E2%80%9CSoaps%E2%80%9D-and-Detergents-Should-They-Be-Used-on-Roses|title="Soaps" and Detergents: Should They Be Used on Roses?|last=Cloyd|first=Raymond A.|date=2018|website=American Rose Society|access-date=4 December 2019|archive-date=15 May 2019|archive-url=https://web.archive.org/web/20190515084621/https://www.rose.org/single-post/2018/03/20/%E2%80%9CSoaps%E2%80%9D-and-Detergents-Should-They-Be-Used-on-Roses|url-status=dead}}</ref> Soaps have a low mammalian toxicity <ref name="label-super"/><ref name="label-mpede"/> and are therefore considered safe to be used around children and pets, and may be used in organic farming.{{citation needed|date=February 2020}}
== Composition == Insecticidal soap's active ingredient is most often a potassium salt of fatty acids.<ref name=":1" /> Insecticidal soap should be based on long-chain fatty acids (10–18 carbon atoms) because shorter-chain fatty acids tend to be damaging for the plant (phytotoxicity).<ref name="rose"/> Short (8-carbon) fatty-acid chains occur for example in coconut oil and soaps based thereon.{{citation needed|date=April 2020}} "'Green Soap' is a potassium/coconut oil soap .... [that] has also been shown to be effective, as an unlabeled insecticide, in controlling soft-bodied insects including aphids".<ref name=":0" /> Recommended concentrations of insecticidal soap are typically in the range 1–2 percent soap mixed with water.<ref name="CSU"/><ref name="UCD"/><ref name="Clemson"/> One manufacturer recommends a concentration of 0.06% to 0.25% (pure soap equivalent) for most agricultural applications.;<ref name="label-super"/><ref name="label-super-conc"/> another one<ref name="label-mpede"/> recommends concentrations of 0.5 to 1% pure soap equivalent. In the European Union, fatty acid potassium salts are registered and allowed as insecticide<ref name="eu-db"/> at a 2% concentration.<ref name="eu-rr-2013"/>
Insecticidal soap is most effective if it is dissolved in soft water, since the fatty acids in soap tend to precipitate in hard water, thereby reducing the effectivity.<ref name="rose"/><ref name="label-super"/>
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 fatty acids" or "potassium laurate" as the active ingredient. Certain types of household soaps (not synthetic detergents,<ref name="rose"/> ) are also suitable, but it may be difficult to tell the composition and water content from the label. Potassium-based soaps{{Broken anchor|date=2024-06-15|bot=User:Cewbot/log/20201008/configuration|target_link=soap#Effect of the alkali|reason= The anchor (Effect of the alkali) has been deleted.}} are typically soft or liquid.
== Mechanism of action == The mechanism of action is not exactly understood.<ref name="rose"/> Possible mechanisms are:<ref name="rose"/><ref name="keeley-youtube"/> * Soap, which enters via the insect's trachea, may disrupt cell membranes, resulting in the cell contents leaking from the damaged cells (cytolysis). * Dissolving the wax layer on the cuticle ("skin"), which leads to water loss by evaporation. * Blocking breathing openings or trachea, which leads to suffocation. * Interfering with growth hormones. * Affecting insect metabolism.
== Affected organisms == Insecticidal soap works best on soft-bodied insects and other arthropods such as<ref name="CSU"/><ref name="label-super"/> aphids, adelgids, mealybugs, spider mites, thrips, jumping plant lice, scale insects, whiteflies, and sawfly larvae. It can also be used for caterpillars and leafhoppers, but these large-bodied insects can be more difficult to control with soaps alone. Many pollinators and predatory insects such as lady beetles, bumblebees, and hoverflies are relatively unaffected. However, soap will kill predatory mites that may help control spider mites.<ref name="CSU"/><ref name="raudonis"/> Also, the soft-bodied aphid-eating larvae of lady beetles, lacewing, and hoverflies may be affected negatively. According to one study<ref name="raudonis"/> a single soap application killed about 15% of lacewing and lady-beetle larvae, and about 65% of predatory mites (''Amblyseius andersoni'').
Green peach aphids are difficult to control<ref name="tremblay-2009"/> since they reproduce quickly (one adult female can deposit up to four nymphs 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<ref name="label-super"/><ref name="label-mpede"/> 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 nymphs die within 48 hours.<ref name="tremblay-2009"/> 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.<ref name="label-super"/><ref name="label-mpede"/> In the European pesticide registration, its use as an insecticide is listed for aphids, white fly, and spider mites.<ref name="eu-rr-2013"/> It may not be used against algae and moss.<ref name="eu-rr-2013"/>
== 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).<ref name="UCD"/><ref name="Clemson"/> Plant injury may not be apparent until two days after application. Some plant species are particularly sensitive to soap sprays. Highly sensitive plants include:<ref name="label-super"/> horse chestnut, Japanese maple (''Acer''), ''Sorbus aucuparia'' (mountain ash), cherimoya fruit, ''Lamprocapnos'' (bleeding heart), and sweet pea. Other sensitive plants include:<ref name="Clemson"/><ref name="label-super"/> ''Portulaca'', some tomato varieties, ''Crataegus'' (hawthorn), cherries, plum, ''Adiantum'' (maidenhair fern), ''Euphorbia milii'' (crown of thorns), ''Lantana camara'', ''Tropaeolum'' (nasturtium), ''Gardenia jasminoides'', ''Lilium longiflorum'' (Easter lily). Conifers 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 stress, young transplants, unrooted cuttings 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,<ref name="label-super"/> as repeated applications may aggravate phytotoxicity. In addition, water conditioning agents can increase phytotoxicity.{{citation needed|date=March 2015}}
Thanks to its low mammalian toxicity, application of insecticidal soap is typically allowed up to the day of harvest.<ref name="label-super"/><ref name="label-mpede"/>
== See also== * Biological pest control * Green pesticide * Insect trap * List of beneficial weeds * List of pest-repelling plants * Organic farming
== References == <references>
<ref name="rose">[https://www.rose.org/single-post/2018/03/20/%E2%80%9CSoaps%E2%80%9D-and-Detergents-Should-They-Be-Used-on-Roses "Soaps" and Detergents: Should They Be Used on Roses?] R.A. Cloyd, American Rose Society (2018).</ref> <ref name="UCD">[https://web.archive.org/web/20000816081247/http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7404.html Aphids: Integrated Pest Management for Home Gardeners and Landscape Professionals]. M.L. Flint, University of California Davis, July 2013.<!--note: date in PDF--></ref> <ref name="CSU">[http://www.ext.colostate.edu/pubs/insect/05547.html Insect Control: Soaps and Detergents]. W.S. Cranshaw, University of Colorado. March 2008.<!--note: date in PDF--></ref> <ref name="Clemson">[http://www.clemson.edu/extension/hgic/pests/pesticide/hgic2771.html Insecticidal Soaps for Garden Pest Control]. J. D. Ubl, Clemson University, July 2009.</ref> <ref name="keeley-youtube">[https://www.youtube.com/watch?v=-qS6nt1zuq8 Insecticidal Soaps - Modes of Action] (video). L.L. Keeley (20 Aug 2013).</ref> <ref name="raudonis">[http://www.lzi.lt/tomai/97(1)tomas/97_1_tomas_str6.pdf 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.</ref> <ref name="label-super">[https://web.archive.org/web/20150402223345/http://www.epa.gov/opp00001/chem_search/ppls/048222-00005-20110721.pdf Pesticide product label for Super insecticidal soap concentrate]. US Environmental protection agency, July 2011.</ref> <ref name="label-super-conc">According to the ''Super insecticidal soap concentrate label'' above: 0.5 pint of a 25% concentrate per 25 gallons = 0.06%.</ref> <ref name="tremblay-2009">[https://www.mysciencework.com/publication/file/1970822/toxicity-effects-of-an-insecticidal-soap-on-the-green-peach-aphid-homoptera-aphididae 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).</ref> <ref name="label-mpede">[https://web.archive.org/web/20150402091823/http://www.epa.gov/opp00001/chem_search/ppls/010163-00324-20110726.pdf Pesticide product label for M-Pede insecticide miticide fungicide]. US Environmental protection agency, July 2011.</ref> <ref name="eu-db">[http://ec.europa.eu/sanco_pesticides/public/index.cfm?event=activesubstance.detail&language=NL&selectedID=1322 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.</ref> <ref name="eu-rr-2013">[http://ec.europa.eu/sanco_pesticides/public/index.cfm?event=activesubstance.ViewReview&id=746 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).</ref>
</references>
Category:Insecticides Category:Sustainable agriculture