Selection and Use of Insecticides for Organic Production - New Mexico State University


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Selection and Use of Insecticides for Organic Production - New Mexico State University

  1. 1. Selection and Use of Insecticides for Organic Production Guide H-168 Tessa Grasswitz1 Cooperative Extension Service • College of Agricultural, Consumer and Environmental SciencesINTRODUCTIONOrganic farming and gardening place a strong em-phasis on non-chemical methods of insect control,chiefly through measures designed to mimic naturalecosystems. These include growing a diversity ofcrops, using only plants that are well-adapted to thesite, practicing crop rotation, building soil health,and encouraging natural predators and parasiticinsects. Many of these tactics are also used by con-ventional growers practicing integrated pest man-agement (IPM). Well-established organic farms and gardens of-ten have very few insect problems. However, pestissues can still arise. Along with native pests, newinvasive species can pose fresh challenges. Addi-tionally, growers transitioning from conventionalsystems may experience particular difficulties inthe first few years of organic production. Underthese circumstances, they may be forced to considerusing a pesticide. There is a common misconcep-tion that because organically approved insecticidesare derived from natural sources they are safer fornon-pest insects. In fact, many of them are toxicto a broad spectrum of insects, including beneficialpredators and parasitic species (Figure 1). Only a Figure 1. Consider potential effects on beneficialvery few materials are highly selective, i.e., harm- insects before spraying insecticides. Larval stagesful to the pest but relatively safe for beneficials. of predators (such as this ladybeetle) are often particularly vulnerable.Furthermore, since the range of chemical controlsavailable to organic growers is much more limitedthan those available to conventional farmers, it is culture (NMDA) for use on the target pest and crop.particularly important to use these products judi- Organic insecticides sold in other states (or on theciously to prevent or delay the development of in- Internet) may not be registered for use here, in whichsecticide resistance. case they are not legal to use in New Mexico. A link Choosing an appropriate insecticide for use in to further information on pesticide regulations inorganic production can be confusing. Bear in mind relation to organic production is provided in the Re-that all insecticides used in New Mexico must be sources section at the end of this publication.registered by the New Mexico Department of Agri-1 Urban/Small Farm Integrated Pest Management Specialist, Department of Extension Plant Sciences, New Mexico State University.To find more resources for your business, home, or family, visit the College of Agricultural, Consumer and EnvironmentalSciences on the World Wide Web at
  2. 2. Certified (or transitioning) organic growers must reasons, highly mobile pests should be sprayed inalso ensure that all the products they use meet the the cool of the early morning when they are rela-requirements of their certifying body and the Na- tively inactive, taking care to avoid spraying flower-tional Organic Program Standards. If a product ing crops where bees might be foraging. Pyrethrumis not included on the list of approved products products are labeled for use against a variety ofmaintained by the Organic Materials Review Insti- pests, including thrips, mites, aphids, various cater-tute (OMRI), then producers should seek further pillars, true bugs, and beetles.advice from their certifier. Certified growers mustalso be able to demonstrate that they have first used ii. Neemall appropriate non-chemical means of control and These products are based on extracts from seeds ofdocumented the conditions justifying the use of an the neem tree, Azadirachta indica, a species native toinsecticide in their organic production plan. As with southern Asia. They may contain neem oil (some-any other pesticide, all organic insecticides should times formulated as a soap) or the purified activebe used only in strict accordance with the directions ingredient, azadirachtin.on the label. Azadirachtin acts mainly as an insect growth Various types of organically approved insecticides regulator, i.e., it disrupts normal growth and de-are discussed below in terms of their active ingre- velopment when applied to immature insects. Fordients. The use of trade names has been kept to a some pests (particularly Lepidoptera [butterflies andminimum since they are subject to change. moths]), it also has anti-feedant and anti-oviposition properties, i.e., it deters them from feeding or laying eggs on treated surfaces. When neem oil is formu-BOTANICAL INSECTICIDES lated as a soap, it acts mainly by disrupting the wa-The following insecticides are derived from plant sources. terproof layer of the insect’s cuticle. Products based on neem work on contact and/ori. Pyrethrum through ingestion. On leaf surfaces, neem is rapidlyPyrethrum is the generic term for several insecti- broken down by sunlight or washed away by rain.cidal compounds (“pyrethrins”) that are found in As with most insecticides, neem should be appliedthe flower heads of the pyrethrum daisy (Chrysan- when target pests are in their early life stages andthemum cinerariaefolium). Do not confuse natural before populations have reached high levels. Evenpyrethrum with synthetic pyrethroids, which have then, repeat applications may be necessary beforesimilar chemical structures but which are not al- effective control is achieved.lowed in organic production. Neem products have been shown to affect over Pyrethrum is a fast-acting contact poison that 200 insect species, including various species of thrips,causes rapid “knockdown” of sprayed insects by leafminers, aphids, scales, caterpillars, beetle larvae,disrupting their nervous system. This initial knock- and some true bugs. Neem is generally considered safedown is followed by paralysis and eventually death. to most adult beneficial insects, but immature stagesHowever, some insects can recover from the knock- (e.g., larval ladybird beetles) are more susceptible.down effect, and for this reason many commercialpyrethrum-based products include synthetic ad- iii. Other botanical insecticidesditives (e.g., piperonyl butoxide) that reduce the A variety of commercial products are based on bo-insect’s ability to detoxify pyrethrum and hence tanical oils or extracts (such as those from garlic orincrease mortality. Products that contain such ad- thyme). In many cases, the modes of action of theseditives, however, are not permitted under the Na- ingredients and their effects on beneficials have beentional Organic Program Standards. little researched and are poorly understood. Some Pyrethrum is a broad-spectrum insecticide that of these products are intended for use as repellentskills insects (including beneficials) on contact; it is rather than control agents, and some of them containhighly toxic to bees, and sprays directly contacting other ingredients that are not permitted under thebees are likely to be lethal. Pyrethrum residues on National Organic Program Standards. If the productplants, however, are rapidly broken down by sun- is not OMRI-approved, producers are advised tolight so that residual activity is limited. For these check with their certifying body prior to use. Guide H-168 • Page 2
  3. 3. MICROBIAL INSECTICIDES world. As with Bt, different insects differ in theirThe following insecticides rely on various microor- susceptibility to different strains, but only a fewganisms or microbial by-products to control insects. strains are currently used in commercial products. Commercial strains are produced by a fermentationi. Bacillus thuringiensis (‘Bt’) process in which the fungal spores are extracted andBacillus thuringiensis is a naturally occurring bacte- formulated into a sprayable product.rium that is common in soil, in dead insects, and Insects become infected with the fungal sporeson plants. It produces both spores (resting stages) either by walking on treated surfaces or through di-and a crystalline protein (endotoxin). When eaten rect contact with the spray. When the fungal sporesby a susceptible insect, the endotoxin is activated contact the insect’s outer surface (cuticle), theand creates holes in the gut wall that allow the spores germinate and send out structures (hyphae)gut contents to enter the insect’s body cavity and that penetrate the insect’s body and proliferate,bloodstream. The insect soon stops feeding and in typically killing the insect in about 3 to 5 days. Thea few days dies of septicaemia; affected insects typi- dead insect then becomes a new source of fungalcally soften and darken as they die. spores, further spreading the infection. Unfortu- Worldwide, there are an estimated 50,000 dif- nately, since the spores are rapidly killed by highferent strains of Bt, and the toxins they contain temperatures and sunlight, these products are mostselectively affect different groups of insects. Com- effective under cool conditions and relatively highmercial products based on Bt typically contain one humidity. They may be suitable for early-season useof the following subspecies: B. thuringiensis kurstaki in hoop houses and similar structures, but are un-(for Lepidopteran larvae, i.e., caterpillar pests), B. likely to work well outdoors in New Mexico in thethuringiensis aizawai (also for Lepidopteran larvae), heat of summer.B. thuringiensis tenebrionis (for beetle larvae; also As with other insecticides that work on contact,known as B. thuringiensis san diego), and B. thuring- good spray coverage is essential, particularly if theiensis israelensis (for fly larvae such as fungus gnats, target insect feeds on the undersides of leaves ormosquitoes, and blackflies). in other protected locations. Multiple applications Not all species of caterpillars, beetles, or flies are may be needed to achieve suppression. Pests thatsusceptible to Bt, but the key to successful use is to bore into the plant are not controlled with thischoose a product containing the subspecies of Bt type of product since they are unlikely to pick upthat is appropriate for the target insect. Since Bt a lethal dose.(like most insecticides) is most effective when ap-plied to young larvae, early detection of the pest is iii. Insect virusesnecessary. Achieving good coverage of treated plants Insects are vulnerable to various naturally occurringis also important, especially since many insects feed viral infections that often cause lethal disease out-on the underside of leaves where they are more pro- breaks when pest populations are high. Such virusestected from sprays. Bt products are broken down are generally very specific to the target insect (andfairly rapidly by sunlight (within a few days) and, hence are safe for beneficial insects), and some havebecause of the specificity of the toxin, are very safe been commercialized as insecticidal products thatfor beneficial insects. can be applied with standard spray equipment. In- Some Bt products may contain additional ingredi- sect viruses are typically covered with a natural pro-ents that are prohibited under the National Organic tein coat that to some extent protects them fromProgram Standards; make sure the product you use rapid environmental degradation when outside ais OMRI-listed and check with your certifier if in living host. To become infected, insects must eatdoubt. Crop plants that have been genetically modi- the virus particles; once inside the highly alkalinefied to produce Bt toxins are also prohibited. environment of the insect gut, the protective coat- ing is broken down, releasing the virus, which thenii. Beauveria bassiana penetrates the cells of the gut wall where it repli-Beauveria bassiana is a soil-dwelling fungus, dif- cates and gradually spreads to other internal organs.ferent strains of which are found throughout the Guide H-168 • Page 3
  4. 4. Typically, infected insects stop feeding within a fewdays, become increasingly inactive, and eventu-ally die. At that point, the body of the insect oftenturns black and soon liquefies, the outer integu-ment (skin) disintegrating to release large numbersof new virus particles, each one of which is capableof starting a new infection if eaten by another hostinsect. Generally, the younger the insect, the moresusceptible they are to infection and the morequickly they will die. Keep in mind that death cantake several days, so large larvae may still cause con-siderable damage before succumbing to infection.In some cases, a sub-lethal infection in a maturelarva may persist into the adult stage, and femalesmay then transmit the infection to their offspringin their eggs. In other cases, mortality from a latentinfection may be delayed until the insect is stressedin some way, for example by lack of food or over-crowding, or during overwintering. Virus particles may persist in protected environ-ments (such as the soil) for some years, and maybe spread by rain, wind, cultivation, and acciden-tal movement by animals. Host-specific sprayableformulations of viruses are currently available forcodling moth (Cyd-X) and corn earworm/tobaccobudworm (Gemstar); however, correct spray tim-ing is critical to ensure success since the larval stageof these insects will bore into their respective hostplants soon after hatching and will then be out ofreach of subsequent sprays (Figure 2). Monitoringwith pheromone traps and correct use of tempera-ture data and development models is recommendedfor these pests. Consult your county CooperativeExtension agent for details. Figure 2. Careful monitoring is needed to time insecticide applications correctly—particularlyiii. Spinosad for pests such as corn earworm that feed withinThe active ingredients in spinosad are derived from the plant.the fermentation of a Caribbean actinomycete (soilbacterium) called Saccharopolyspora spinosa. Prod- reduced. Spinosad-based products are principallyucts based on spinosad disrupt the insect nervous used against caterpillar pests (Lepidoptera), thrips,system, leading to loss of muscle control and even- fruit flies, sawflies, and some pest beetles (e.g.,tually paralysis and death. Insects pick up a lethal the larval stages of Colorado beetles). Spinosad isdose by eating treated plants or by direct contact not fully systemic (able to move within the plant),with a spray droplet or the residue on newly treated but penetrates leaves well enough that it can besurfaces. Affected insects are killed in 1 to 2 days. used against some species of leafminers. Spinosad Spinosad is relatively safe to many important products have been widely used by organic growerspredatory insects, but is toxic to bees and para- against codling moth, but the risk of developingsitic wasps if they are contacted directly by spray resistance makes it inadvisable to use it every gen-droplets; once the residues dry, their toxicity is eration. If possible, use correctly timed applications Guide H-168 • Page 4
  5. 5. of Bt-based products (or Cyd-X) against at least thefirst generation, which tends to be less numerousthan the later ones.OTHER ORGANICALLY APPROVEDINSECTICIDESi. Insecticidal soapsInsecticidal soaps are sprayable liquid formulationsof potassium salts of fatty acids that are specificallyintended for insect control. They work by degrad-ing the outer waterproof layer of the insect cuticleso that the pest dies from desiccation. Soaps workbest against soft-bodied pests such as aphids, mites,mealybugs, and the immature stages of other pests;predatory mites and the soft-bodied larval stages ofbeneficial insects such as ladybird beetles (“ladybugs”)and hoverflies are also likely to be affected. Soapsare ineffective against insect eggs and harder-bodiedadult insects. Some soap-based products are formu-lated with neem oil, and these tend to have a broaderrange of action (see previous section on neem). Target pests must be directly contacted by thespray; once the residue dries on the plant, it is nolonger effective. For this reason, it is more effectiveto spray in the early morning when the insects arebecoming active but temperatures are still relativelycool so that drying is less rapid. Repeat applicationsmay be necessary to achieve control. Be aware that although insecticidal soaps areformulated to be non-toxic to plants (unlike dish Figure 3. Tomato plant treated with kaolin clay.soaps), they may still disrupt the waterproof layerof leaves (particularly those with a dense layer ofwax); check the label recommendations for suscep- iii. Kaolin claytible crop types and, if in doubt, spray only a por- Kaolin is a naturally occurring clay mineral that istion of the plant and wait for several days to check finely ground and processed to produce a sprayablefor adverse effects before proceeding further. material that dries to a fine white film after being applied to leaves, stems, and fruits (Figure 3). Itii. Horticultural oils acts against insects in several ways: it can form aOMRI-listed horticultural oils are based either physical barrier that prevents them from reachingon vegetable products (such as canola oil) or light the plant tissue, act as a repellant (deterring feedingmineral oils. They are combined with emulsifiers to and egg-laying), mask the attractant properties ofhelp disperse them in water for spraying. These oils treated plants, and act as an irritant. In regions withwork by physically clogging the insect’s breathing high summer temperatures and light intensity, it ispores (spiracles), and good coverage to directly con- also used to protect tree fruits (e.g., apples) fromtact the pest is therefore essential. There may be a sunburn and to reduce plant stress by reducingrisk of phytotoxicity (damage to the plant) if these water loss through transpiration. In some regions,products are applied when temperatures are high. kaolin clay has been shown to be effective againstCheck product labels for details. some orchard pests (e.g., apple maggot) and to give Guide H-168 • Page 5
  6. 6. fair control of codling moth; however, heavy usehas been found to be harmful to some beneficialspecies and in some cases this has resulted in out-breaks of scale and mite pests. To be effective, complete coverage of the plantis necessary, which can be difficult to achieve withbackpack equipment and home garden sprayers.Bear in mind, too, that actively growing plants willsoon produce new (unprotected) leaves and thatheavy rain will reduce the clay deposits. Further-more, residues remaining on the crop at harvest arelikely to reduce marketability if not removed.iv. Diatomaceous earthDiatomaceous earth is a fine powder formed fromthe silica-rich “skeletons” of tiny marine plants (dia-toms). This material acts by absorbing the waxesfrom the waterproof layer of the insect’s cuticle sothat the pest eventually dies through desiccation.Although there are organically approved productsbased on this material, their registered uses arelimited mainly to control of ants and similar pestsaround dwellings. Very few plant-feeding pests areincluded under present product registrations.v. Sucrose estersAt present, there is only one product based onsucrose esters; sold under the brand name Su-craShield, it is used as a foliar spray to control or Figure 4. Increasing diversity in the farm andsuppress soft-bodied pests such as aphids, mealy- garden can help reduce pests and hence the needbugs, leafhoppers, mites, thrips, caterpillars, and for insecticides.some scale insects. It acts by creating minute holesin the insect’s waterproof coating so that the pesteventually dries out and dies through desiccation. choice of crops and cultivars to suit the site, cropAs with other pesticides targeted at soft-bodied in- rotation, sanitation, and conservation biologicalsects (e.g., insecticidal soaps), it will affect beneficial control (Figure 4). Certified organic producersinsects that are in a vulnerable stage (e.g., ladybeetle (or those seeking certification) should consider alllarvae) if they are directly contacted by the spray. available options for managing the pests they areThe residues are broken down to sugar, fatty acids, likely to encounter and include this information incarbon dioxide, and water. their organic management plan; if they wish to use a product not included in their management plan, they must first seek approval from their certifyingUSE OF ORGANIC INSECTICIDES body and must ensure that the product chosen isPesticides should only be used as part of an inte- both registered for that purpose with the New Mex-grated pest management (IPM) strategy. This is ico Department of Agriculture (NMDA) and eitherparticularly true in organic growing systems where approved by the Organic Materials Review Institutethe primary emphasis should be on adopting a (OMRI) or their certifier. Both OMRI and theholistic approach to pest prevention that includes NMDA maintain searchable, online product data-building soil health and organic matter, careful bases (see Resources section for links). Guide H-168 • Page 6
  7. 7. SAFE USE OF INSECTICIDES RESOURCESIf it becomes necessary to use insecticides, use them New Mexico Department of Agriculture (NMDA).wisely and safely. The following tips will help you Searchable database of pesticides registered formake better use of these products. use in New Mexico: http://state.ceris.purdue. edu/doc/nm/statenm.html• Try to monitor for pests at least once per week. Organic Materials Review Institute (OMRI). Pay particular attention to the undersides of Searchable database of products and generic leaves where mites, whiteflies, aphids, and many materials currently approved for organic produc- insect eggs are often found. It is important to tion: apply insecticides at the right time—preferably Caldwell, B., E.B. Rosen, E. Sideman, A.M. Shel- when the pest is in the immature stages (Figure ton, and C.D. Smart. 2005. Understanding 2). Be sure that you have correctly identified the pesticide regulations. In Resource guide for organic insect. If in doubt, consult your county Exten- insect and disease management [Online]. Avail- sion agent. able from resourceguide/appendix/appendix_e.php• With many organically approved insecticides, good plant coverage is essential to achieve con- trol. Do not apply insecticides to wilted plants Tessa Grasswitz is NMSU’s urban/ or during the hottest part of the day, or if wind small farm integrated pest management speed is more than 5 to 10 miles per hour. Re- specialist. Her research interests include peated application may be necessary after heavy integrated control of insect pests, conserva- tion of native pollinators, and the interac- rain; check product label for details. tions between soil heath, plant pests, and biological control agents. Her Extension• Apply insecticides only at the dosages recom- program provides research-based pest mended on the product label. Larger amounts management information to small-scale commercial growers, home gardeners, and can be dangerous, cause plant damage, and leave landscape professionals. harmful residues without improving insect con- trol.• The length of effective control provided by an insecticide varies widely, not only with the active ingredient and its formulation but also with the pH of the water used for mixing and with envi- ronmental conditions. Temperature, humidity, wind, and sunlight can all affect insecticide resi- dues on the plant; the greater the extremes, the sooner the insecticides will be degraded.• The time interval required by the Environmental Protection Agency between treating a crop and harvesting that crop (the “pre-harvest interval”) varies with both the product and the crop. This interval is stated on the product label and is set at a level that ensures that any residues left at the time of harvest will be within acceptable limits.• Always read and follow all instructions on the product label for safe and effective insect control. Guide H-168 • Page 7
  8. 8. DISCLAIMER: Brand names appearing in publications are for product identification purposes only. No endorsement is intend- ed, nor is criticism implied of similar products not mentioned. Persons using such products assume responsibil- ity for their use in accordance with current label directions of the manufacturer. Please be aware that pesticide labels and registration can change at any time. By law, it is the applicator’s respon- sibility to use pesticides ONLY according to the directions on the current label. Use pesticides selectively and care- fully, and follow recommended procedures for the safe storage and disposal of surplus pesticides and containers.Contents of publications may be freely reproduced for educational purposes. All other rights reserved. For permission to usepublications for other purposes, contact or the authors listed on the publication.New Mexico State University is an equal opportunity/affirmative action employer and educator. NMSU and the U.S. Departmentof Agriculture cooperating.May 2012 Las Cruces, NM Guide H-168 • Page 8