Plant Essential Oils

General Information:

Many plant essential oils show a broad spectrum of activity against pest insects and plant pathogenic fungi ranging from insecticidal, antifeedant, repellent, oviposition deterrent, growth regulatory and antivector activities. http://projects.nri.org/adappt/docs/63-84.pdf

As such, they have considerable potential as crop protectants and for pest management in other situations (e.g. urban pest control). Current information indicates that they are safe to the user and the environment, with few qualifications. As a cautionary note, the essential oils that are most eficacious against pests are often the most phytotoxic; this latter property requires serious attention when formulating products for agricultural and landscape use. Also, selectivity among invertebrates is not well documented. Honeybees appear somewhat susceptible (Lindberg et al., 2000), and the susceptibility of various natural enemies has yet to be reported, although the lack of persistence of essential oils under field conditions could provide some measure of temporal selectivity favoring these non-target species. Like other alternative pest management products, essential oil-based pesticides will not be a panacea for crop protection, but there should be substantial market niches, particularly where there is a premium on worker safety and environmental protection, in which these types of products will find wide acceptance among growers.

Among the best known essential oils with bioactivity against insects and other pests are clove oil (eugenol), thyme oil (thymol, carvacrol), mint oil (menthol, pule-gone), lemongrass oil (citronellal, citral), cinnamon oil (cinnamaldehyde), rosemaryoil (1,8-cineole) and oil of oregano (carvacrol). Pesticides based on plant essential oils: from traditional practice to commercialization

Steam distillation of aromatic plants essential oils are produced commercially from botanical sources, many of which are members of the mint family. They have been demonstrated to have fumigant and contact insecticidal activities to a wide range of pests The rapid action against some pests is indicative of a neurotoxic mode of action. Owing to their volatility, essential oils have limited persistence under field conditions; therefore, although natural enemies are susceptible via direct contact, predators and parasitoids reinvading a treated crop one or more days after treatment are unlikely to be poisoned by residue contact with pesticides.

Among the natural products used for pest control, one of the most successful botanical pesticide groups are monoterpenoids, which are mostly found in plant essential oils. Monoterpenoids are related to or derived from monoterpenes, a class of terpenes, containing two units of isoprene, and are 10-carbon molecules. These compounds are plant secondary metabolites and play a key role in defending the plants against herbivores or pathogens. For hundreds of years, monoterpenoids have been widely used as food additives, fragrances, decongestants, external analgesics, and antimicrobials (FANG, 2010).

Tong, Fan, "Investigation of mechanisms of action of monoterpenoid insecticides on insect gamma-aminobutyric acid receptors and

nicotinic acetylcholine receptors" (2010). Graduate eses and Dissertations. Paper 11665.

Essential oils contained in pest control products will have their own application rates. If you are making your own essential oil spray follow these instructions provided by BuildASoil:  "The Essential oils were tested throughout the studies at various levels and found to burn plants with doses that were too high especially if administered while lights are on. Use essential oils during lights out ONLY. The best effects were around 1% essential oils by volume and as such we recommend using .5 1% essential oils for our mixtures and to test in a small amount first." PLANTS PRODUCE OILS AS SECONDARY METABOLITES. VARIATIONS IN OIL CONCENTRATIONS WILL BE DEPENDENT ON GROWING CONDITIONS AND PLANT VARIETIES.

 
 
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Rosemary

Rosemary oil repels both spider mites and whiteflies. Rosemary oil and rosemary oil-based pesticides are non-persistent in the environment and their lethal and sub-lethal effects fade within one or two days.

Residues of all pesticides with rosemary as the active ingredient were found to be moderately toxic to spider mites within the first hour after spraying. However, toxicity decreased significantly after 24 hours. This clearly highlights that rosemary is not persistent in the environment due to its volatile nature.https://open.library.ubc.ca/cIRcle/collections/ubctheses/831/items/1.0092479


The residues of all pesticides containing rosemary did not show significantly statistic toxicity to the predator mite P. persimilis. This indicates a positive IPM program that can be implemented with rosemary oil and P. persimilis.

Rosemary oil was slightly toxic to whiteflies but not significantly toxic after 24 hours.

 
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Oregano

The active ingredient in oregano oil is carvacrol. Carvacrol has broad insecticidal and acaricidal activity against pests and it acts as a fumigant. It is highly toxic to the mite, Tetranychus urticae (Isman 2000) Isman MB. Plant essential oils for pest and disease management. Crop Protection. 2000;19:603–608.

Carvacrol is clearly active against most fungal species tested. The mechanism of action of these compounds against fungi is unknown but may be related to their general ability to dissolve or otherwise disrupt the integrity of cell walls and membranes. As a cautionary note, many of these oils and pure compounds show considerable phytotoxicity to plants at concentrations only slightly above those required for control of plant pathogenic fungi, presumably because plant cells are affected by a similar mechanism. (Murray B. Isman, Nov 21, 2014.)

Target Pests & Diseases:   Spider Mites, Botrytis cinerea, Monilinia fructicola, Rhizoctonia solan, Fusarium moniliforme, Sclerotinia sclerotiorum, Aspergillus spp.

 
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Thyme

The active ingredient in thyme oil is thymol.

Thymol is clearly active against fungal pathogens. The mechanism of action of these compounds against fungi is unknown but may be related to their general ability to dissolve or otherwise disrupt the integrity of cell walls and membranes. As a cautionary note, many of these oils and pure compounds show considerable phytotoxicity to plants at concentrations only slightly above those required for control of plant pathogenic fungi, presumably because plant cells are affected by a similar mechanism. (Murray B. Isman, Nov 21, 2014.) 

thyme oil showed the highest ovicidal activity

Half Life of Thymol: 5 days soil, 16 days water (FANG, 2010).

Target Pests & Diseases:   Spider Mites, Botrytis cinerea, Monilinia fructicola, Fusarium moniliforme, Sclerotinia sclerotiorum, Aspergillus spp., Fusarium solani, Rhizoctonia solani, Pythium ultimum

 
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Sage

Salvia officinalis (sage, also called garden sage, common sage, or culinary sage) is a perennial, evergreen subshrub. The essential oil contains cineole, borneol, and thujone. The essential oils in which thujone occurs are used for mite repellants. Much about sage is anecdotal and we can only surmise its affects based on the chemical compositions of its essential oil production.

Commercial preparations of essential oils of sage, thuja, and cedar which contain thujone have caused central nervous system effects. At a concentration of 4%, alpha-thujone was negative in dermal irritation and maximization tests in humans (FEMA, 1997).

FEMA (1997) FEMA Database: Thujone, Washington, DC, Flavor and Extract Manufacturer's Association, 12 pp

Target Pests & Diseases:   Spider Mites


 

 

 
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Peppermint/

Peppermint (Mentha × piperita, also known as Mentha. balsamea Willd is a hybrid mint: a cross between watermint and spearmint. Peppermint has a high menthol content. The oil contains menthone and varying amounts of many additional compounds including limonene, cineol, pulegone, beta-caryophyllene and beta-pinene.

Peppermint oil has a high concentration of natural pesticides, mainly pulegone (Found mainly in Mentha arvensis var. piperascens Cornmint, Field Mint, Japanese Mint and to a lesser extent-6,530 ppm in Mentha x piperita subsp. nothosubsp. piperita[16]) and menthone.[17]

The chemical composition of the essential oil from peppermint (Mentha x piperita L.) was analyzed by GC/FID and GC-MS. The main constituents were menthol (40.7%) and menthone (23.4%). Further components were (+/-)-menthyl acetate, 1,8-cineole, limonene, beta-pinene and beta-caryophyllene.

A 72 hour enclosed vapor test showed pulegone having100% kill rate with methanol at 39% and menthone at 17% death of spider mites. Phenolic compounds of peppermint also act as feeding deterrents. http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/41829/LarsonKatherineCole1983.pdf;sequence=1

Phenolic compounds in cucumbers were observed to be eleveated

Target Pests & Diseases:   Spider Mites, Fungus Gnats

 
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Lavender

The exact composition of lavender essential oil varies from species to species but consists primarily of monoterpeneoids and sesquiterpeneoids. Of these linalool and linalyl acetate dominate, with moderate levels of lavandulyl acetate, terpinen-4-ol and lavandulol. 1,8-cineole and camphor are also present in low to moderate qualities. In all lavender oil typically contains many more than 100 compounds, although a great many of these are present at very low concentrations.(Shellie, Robert; Mondello, Luigi; Marriott, Philip; Dugo, Giovanni (2002). "Characterisation of lavender essential oils by using gas chromatography–mass spectrometry with correlation of linear retention indices and comparison with comprehensive two-dimensional gas chromatography". Journal of Chromatography A. 970 (1-2): 225–234. doi:10.1016/S0021-9673(02)00653-2. ISSN 0021-9673.)

Mode of action:

Target Pests and Diseases: 

 

 
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Eucalyptus

Source: Cineole-based eucalyptus oil is used as an insect repellent and biopesticide. In the U.S., eucalyptus oil was first registered in 1948 as an insecticide and miticide. The eucalyptus genus also produces non-cineole oils, including piperitone, phellandrene, citral, methyl cinnamate and geranyl acetate.

Mode of action: The oil possesses a wide spectrum of biological activity including anti-microbial, fungicidal, insecticidal/insect repellent, herbicidal, acaricidal and nematicidal. Eucalyptus oil is a complex of a variety of monoterpenes and sesquiterpenes, and aromatic phenols, oxides, ethers, alcohols, esters, aldehydes and ketones; however, the exact composition and proportion of which varies with species. The pesticidal activity of eucalyptus oils has been due to the components such as 1,8-cineole, citronellal, citronellol,citronellyl acetate, p-cymene, eucamalol, limonene, linalool, a-pinene.

Target Pests and Diseases:  Spider Mites, Root Knot Nematodes, Botrytis cinerea, Fusarium oxysporum, Pythium ultimum, Rhizoctonia solani and Phytophthora capsici

Eucalyptus essential oil as a natural pesticide Forest Ecology and Management
Volume 256, Issue 12, 10 December 2008, Pages 2166–2174.

 

 
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Clove

Source: Cloves are the aromatic flower buds of a tree in the family Myrtaceae, Syzygium aromaticum. Eugenol is a phenylpropene and is the active ingredient in clove.

Mode of action: Eugenol composes 72–90% of the essential oil extracted from cloves and is the compound most responsible for clove aroma. Other important essential oil constituents of clove oil include acetyl eugenol, beta-caryophyllene and vanillin, crategolic acid, tannins such as bicornin, gallotannic acid, methyl salicylate, the flavonoids eugenin, kaempferol, rhamnetin, and eugenitin, triterpenoids such as oleanolic acid, stigmasterol, and campesterol and several sesquiterpenes.

Target Pests and Diseases:  Aphids, Whiteflies, Thrips, Spider Mites, Botrytis cinerea

Antifungal activity of eugenol against Botrytis cinerea

 
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Citrus Oil Extracts

Source: Crude citrus oils and the refined compounds d-limonene (hereafter referred to simply as limonene) and linalool are extracted from orange and other citrus fruit peels. Limonene, a terpene, constitutes about 90% of crude citrus oil, and is purified from the oil by steam distillation. Linalool, a terpene alcohol, is found in small quantities in citrus peel and in over 200 other herbs, flowers, fruits, and woods.

Mode of action: The modes of action of limonene and linalool in insects are not fully understood. Limonene is thought to cause an increase in the spontaneous activity of sensory nerves. This heightened activity sends spurious information to motor nerves and results in twitching, lack of coordination, and convulsions. The central nervous system may also be affected, resulting in additional stimulation of motor nerves. Massive over stimulation of motor nerves leads to rapid knockdown paralysis. Adult fleas and other insects may recover from knockdown, however, unless limonene is synergized by PBO. Linalool is also synergized by PBO. Little has been published regarding the mode of action of linalool in insects.

Citric acid contains broad-spectrum antifungal and antibacterial compounds.

Target Pests and Diseases:  Aphids, Whiteflies, Leaf Hoppers, Spider Mites

Texas A&M University - Department of Entomology

 
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Lemongrass

Source: The oil of lemon grass is extracted from fresh or dried lemon grass by steam distillation or simply by pouring boiling water over the foliage. The composition of lemon grass oil depends partly on geographical region or where it is grown. Major constituents of lemon grass oil are citral, geraniol, myrcene, citronellal and limonene. Citronella oil, which repels mosquitoes, contains large amounts of citral. Citral gives lemon grass oil its lemony fragrance. Lemongrass oil is used as a pesticide and a preservative. Research shows that lemongrass oil has antifungal properties.

Mode of action: The modes of action of are similar to that of citrus oil extracts

Target Pests: