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Cooperative Extension Service College of Agriculture and Home Economics

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Organic GardeningNaturalInsecticidesGuide H-150

L.M. EnglishExtension Entomologist

This publication is scheduled to be updated and reissued 7/10.

Despite our best efforts, nonchemical methods some-times fail to prevent excessive insect damage in thegarden. At such times, the use of insecticides may bethe only alternative left to save the crop. When damagebecomes great enough to warrant emergency measures,organic gardeners often will want to use natural insecti-cides and various homemade botanical sprays, instead of

synthetic organic chemicals.The insecticide used should have low toxicity to manand to other warm-blooded animals. Insecticides shouldbe used only when needed and in strict accordance withlabel directions. A good understanding of insecticides al-lows these materials to be used effectively without harm-ing you or the environment.

The following information may help New Mexico gar-deners select a natural insecticide for their specific needs:

PyrethrumBotanical insecticide. This slightly toxicinsecticide is derived from the flowers of a species ofchrysanthemum imported mainly from Kenya andEcuador. The material causes rapid paralysis of most

insects, but the insects usually recover unless the py-rethrum is combined with a synergist or other poison.Pyrethrum mixed with synergists such as piperonylbutoxide or piperonyl cyclonene increases toxicity andproduces longer, residual action, and is used extensivelyin space sprays, household sprays, crop sprays and dusts.This chemical is registered for use on most vegetablesand fruits at any time during the growing season.

NicotineBotanical insecticide. Pure nicotine is atobacco extract highly toxic to warm-blooded animals.The insecticide usually is marketed as a 40% liquidconcentrate of nicotine sulfate, which is diluted in waterand applied as a spray. Dusts can irritate the skin and are

not normally available for garden use. Nicotine is usedprimarily for piercing-sucking insects such as aphids,whiteflies, leafhoppers and thrips. Nicotine is more ef-fective when applied during warm weather. It degradesquickly, so it can be used on many food plants nearingharvest. It is registered for use on a wide range of veg-etable and fruit crops.

SabadillaBotanical insecticide. Sabadilla is obtainedfrom the seeds of a lily-like plant and acts as both a con-tact and stomach poison for insects. It is not particularlytoxic to mammals, but it does cause irritation of theeyes and respiratory tract. A mask should be worn whenworking with this insecticide. This material deterioratesrapidly when exposed to light and can be used safely on

food crops shortly before harvest. Generally Sabadilla isused as a 5 to 20% dust or as a spray.RotenoneBotanical insecticide. Rotenone is ex-

tracted from the roots of derris plants in Asia and cubeplants in South America. This general garden insecticideis harmless to plants, highly toxic to fish and manyinsects, moderately toxic to mammals, and leaves noharmful residue on vegetable crops. It acts as both acontact and stomach poison to insects. It is slow actingand, in the presence of sun and air, its effectiveness islost within a week after application. Wear a mask duringapplication because rotenone can irritate the respiratorytract. Rotenone dusts and sprays have been used for

years to control aphids, certain beetles and caterpillarson plants, as well as fleas and lice on animals.

NeemBotanical insecticide. Neem oil is an extractfrom the Neem tree, Azadirachta indica (Meliaceae).The neem tree is native to Southeast Asia and growsin many countries throughout the world. It is a closerelative to the common Chinaberry tree. This treepropagates readily from cuttings, stumps, tissue cultureor seeds. It is widely used as a shade tree in many areasbecause it tolerates a wide range of conditions. Theneem tree has many medicinal uses. It has been used asan antiseptic and diuretic. It has been used to cure dis-ease from diabetes to syphilis, and widely relied upon by

herbalists in its native habitat. The uses of the neem treeas a source of natural insecticides was discovered over40 years ago.

The seeds of the neem tree contain the highestconcentration of azadirachtin and other biologicallyactive compounds. Because they contain the highestconcentration of these compounds, most experimentaland commercial preparations of neem are seed extracts.

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Some of the commercial insecticides registered by EPAare: Turplex, Neemguard, Margosan-0, Wellgro, Repe-lin, Neemis, NeemazaL and Neemark.

These products generally are well known for their an-tifeedant activity. The Lepidoptera (moths and butterfliesand their larvae) are the most affected order of insects.These compounds also act as growth regulators, which

causes some larvae to remain in a permanent larval stage.Registered pesticide labels may vary, and you shouldcarefully study the label before use.

Other PesticidesGardeners have been using soap to control insects sincethe early 1800s. During the first half of the 19th century,whale oil soap and, more commonly, fish oil soaps werean important part of insect control. Recent tests indicateIvory Liquid dishwashing detergent, when diluted withwater to a 1 to 2% solution, provides the most consistentcontrol and is easy to mix. There are also soaps avail-able that are specifically formulated to control insects on

plants. Thorough coverage of the plant and repeated ap-plications may be necessary to bring insect populationsunder control. High rates of soaps and detergents maydamage some varieties of plants. The most effective soapshave carbon chains of C-12 or C-18. Laurate (C-12) isthe main component of most dishwashing liquids andvarious other products in common usage. The richestnatural source of this is coconut oil.

Organic gardeners have been using a spray mixtureof onions, garlic and pepper to control insects for manyyears. Recent scientific research indicates using this mix-ture has been erratic and, in many cases, ineffective forinsect control. Sprays of food-derived substances may

have no or sporadic success.Spraying several times a week may help to bring

infestations under control. Expecting control withone application is unrealistic.

Safe Use of PesticidesWhen it is necessary to use insecticides to protect thegarden, use them wisely and safely. The following tipswill help you make better use of insecticides. Inspect the entire garden at least weekly to monitor

insect numbers and activity. Pay particular atten-tion to underside of leaves where mites, whiteflies,aphids and insect eggs occur. If treatments are appliedwhen an infestation first starts, insect numbers canbe maintained at lower levels much more easily, andwith smaller amounts of chemicals.

Apply insecticides to all plants surfaces so an insectanywhere on the plant will be exposed to a lethalamount of the chemical. Do not apply insecticidesto wilted plants or during the hottest part of the day.Apply dusts only when the wind is calm and plantsare dry. Sprays should be applied when the wind isno more than 5 to 10 miles per hour. Repeated treat-

ment may be necessary after a rain. Apply insecticides only at recommended dosages.

Increased amounts can be dangerous, cause plantdamage and leave harmful residues without improv-ing insect control.

The length of effective control with insecticides varieswidely. The longevity of toxic properties varies pri-marily with the product, formulation, water, pH andenvironmental conditions. Temperature, humidity,wind and sunlight affect insecticides. The greater theextremes, the sooner the insecticides are detoxified.

The time interval required by the Environmental

Protection Agency between treating a crop and har-vesting that crop varies with the insecticide and thecrop. This information is printed on the pesticidelabel to ensure that any residues will be within estab-lished tolerances at harvest time.

Always read and follow mixing and application in-structions on the insecticide label for safe and effec-tive insect control.

Some synthetic organic materials are actually less tox-ic and more efficient than some natural insecticides.Because a material is a natural pesticide, it does notnecessarily follow that it is not toxic to man or harm-ful to the environment if used improperly.

In most situations it is helpful to use several controltechniques to reduce insect pest populations to lowenough levels that insecticides are not required, or areneeded only sparingly. With reduced insecticide use,biological control agents can become more effective, in-secticide costs will be saved, and you will have the satis-faction of knowing that few, if any, poisons were appliedto edible crops.

New Mexico State University is an equal opportunity/affirmative action employer and educator. NMSU and the U.S. Departmentof Agriculture cooperating..Revised July 2005 Las Cruces, NM

The information given herein is supplied with the

understanding that no discrimination is intendedand no endorsement by the New Mexico CooperativeExtension Service is implied.