- Author: Surendra K. Dara
- Author: Sumanth S. R. Dara
- Author: Suchitra S. Dara
- Author: Ed Lewis
A study was conducted in the summer of 2017 to evaluate the efficacy of various chemical, botanical, and microbial pesticides against arthropod pests on zucchini. Zucchini plants initially had a high aphid infestation, but populations gradually declined due to natural control by lady beetle activity. However, heavy silverleaf whitefly (Bemisia tabaci) infestations developed by the time the study was initiated. Other pests that were present during the study period were aphids (possibly melon aphids), the western flower thrips (Frankliniella occidentalis), and the pacific spider mite (Tetranychus pacificus).
Experiment was conducted using a randomized complete block design with 10 treatments. Each treatment had two 38” wide and 300' long rows of zucchini replicated four times. Treatments included i) untreated control, ii) Sivanto 200 SL (flupyradifurone) 14 fl oz/ac, iii) Sequoia (sulfoxaflor) 2.5 fl oz/ac, iv) Venerate XC (heat-killed bacterium, Burkholderia rinojensis strain A396) 4 qrt/ac, v) PFR-97 20% WDG (entomopathogenic fungus, Isaria fumosorosea Apopka strain 97) 2 lb/ac, vi) I1800AA (undisclosed botanical extract) 10.3 fl oz/ac, vii) I1800A 12.7 fl oz, viii) I1800A 17.1 fl oz, ix) I1800A 20.5 fl oz, and x) VST-00634LC (based on a peptide in spider venom) 25%. A spray volume of 50 gpa for all treatments except for VST-00634LC, which had 25 gpa. Treatments were applied on 28 August and 4 September, 2017 using a tractor-mounted sprayer with three Teeject 8003vs flat spry nozzles that covered the top and both sides of each bed.
Pest populations were counted before the first spray application and 4 days after each application. On each sampling date, one mid-tier leaf was collected from each of the five randomly selected plants within each plot. A 2-square inch disc was cut out from the middle of each leaf and the number of aphids, eggs and nymphs of silverleaf whitefly, larvae of western flower thrips, and eggs and mobile stages of pacific spider mite were counted under a dissecting microscope. Data were analyzed using Statistix software and Tukey's HSD test was used to separate significant means.
Efficacy varied among different treatments and for different pests.
Aphid: There was a general decline in aphid populations during the study period and there was no difference (P > 0.05) among the treatments (Fig. 1).
Western flower thrips: Nymphal numbers declined in most of the treatments during the observation period (Fig. 2). However, significant differences (P = 0.0220) only after the second spray application where Sivanto treatment had significantly fewer thrips than Venerate treatment (Fig. 2). There was a 92.5% decline by the end of the study, compared to the pre-treatment counts, from PFR-97 application, followed by 88.1% decline in Sivanto, 85.4% in VST-00634, and 82.9% in I1800AA at 10.3 fl oz.
Pacific spider mite: There was an increase in mite eggs in all treatments after the first spray application followed by a decline after the second one without significant differences (P > 0.05) (Fig. 3) Similar trend was also seen in mobile stages in some treatments. Number of mobile stages was significantly different (P = 0.0025) only after the first spray where untreated control, PFR-97, Venerate, and I1800AA at 20.5 fl oz had the lowest. When percent change in egg numbers from the pre-treatment counts, only I1800AA treatments reduced egg numbers after the second spray with a 33.8% decline at 10.3 fl oz rate, 35.7% at 20.5 fl oz, and 60% at 17.1 fl oz. There was also a decline in the mobile stages after the second spray with 54.1% reduction in untreated control to 67.7% in PFR-97 treatment.
Silverleaf whitefly: There was a general increase in the egg and nymphal stages of whitefly during the study (Fig. 4). Significant differences were seen pre-treatment counts of egg (P = 0.0330) and nymphal stages (P = 0.0011), and after the second spray in nymphal stages (P = 0.0220). Compared to the untreated control, both Sivanto and Sequoia resulted in a significant reduction in egg numbers after the first spray, whereas Sequoia, Venerate, and I1800AA at 20.5 fl oz reduced nymphal stages after the second spray. When the percent change from the pre-treatment counts was compared, only Sivanto and Sequoia reduced whitefly egg numbers after both sprays. There was also a reduction in eggs after the first spray from I1800AA at 17.1 fl oz. However, there was a reduction in nymphal stages after the first spray in Sivanto, I1800AA at 17.1 fl oz, and VST-00634, and after the second spray in Sivanto, Sequoia, Venerate, and I1800AA at 17.1 and 20.5 fl oz.
All arthropod pests: When all data were combined for different pests and their life stages, Sivato, Sequia, and PF-97 resulted in a significant (P = 0.0001) decline in pest numbers compared to untreated control after the first spray. Only Sivanto and Sequoia caused such a reduction (P = 0.0048) after the second spray.
In general, both the chemical pesticides (Sivanto and Sequoia) provided a very good pest control. The efficacy of the botanical extract was moderate to good depending on the pest, life stage, or the application date. Spider venom-based product also provided a good control while microbial products had a moderate impact. Although chemical pesticides appeared to be very efficacious, non-chemical alternatives were also effective. It is important to consider all these options to apply in combinations or rotations to obtain desired pest suppression without posing the risk of insecticide resistance.
Acknowledgements: Thanks for the financial support of Arysta LifeScience, CertisUSA, Dow AgroSciences, and Vestaron, and the technical assistance of Neal Hudson.
- Author: Melissa O'Neal, Marrone Bio Innovations
- Author: Surendra K. Dara
Biopesticide refers to a pesticide which originates from animals, microorganisms, or plants. In addition to preventing yield losses through pest and disease control, biopesticides improve environmental and human health by contributing to the reduction of chemical pesticides as well as by improving the quality of produce (Popp et al., 2012). Additionally, these products have the potential to improve harvest and shipping flexibility, assist with environmental stewardship, and assist growers to achieve sustainability goals. Biopesticides are also important tools in integrated pest management (IPM) programs and reducing the risk of resistance to chemical pesticides (Pretty and Bharucha, 2015), improving worker safety through short restricted entry intervals (Valland, n.d.), conserving natural enemies, and maintaining environmental health (EPA, 2017a).
Biopesticides are inherently less toxic than conventional pesticides. Most affect only the target pest and closely related organisms, in contrast to broad spectrum conventional pesticides that may affect nontarget organisms such as beneficial insects, birds, wildlife, aquatic animals, and mammals. The majority of biopesticides often rapidly decompose, resulting in decreased exposure as well as preventing many pollution problems commonly associated with conventional pesticides. Although relatively safer than chemical pesticides, users or applicators should follow safety guidelines and wear personal protective equipment according to the label directions (EPA, 2017a). It is also important to follow guidelines for spray volume, application rates, droplet size, water pH, compatibility with tank-mix partners, time and frequency of application, and other details to ensure efficacy of the biopesticides (van Zyl et al., 2010; Wang & Liu, 2007; Whitford et al., 2009).
Biopesticides use has been increasing in the recent years. They can be used as standalone treatments or combined or rotated with other pesticides in both organic and conventional production systems. The fact that there are no residues is a huge benefit for exported commodities, as maximum residue limit issues continue to be a challenge in this arena (Berger, 2013).
In expanding upon the role of biopesticides in biocontrol, the topic of resistance management is a key consideration. Pest resistance to conventional chemical pesticides is a significant concern. Scientific research has repeatedly demonstrated that continuous use of the same class of pesticides, especially those reliant on a single mode of action, will result in the emergence of a pest population resistant to those products (Osteen et al., 2012). Populations of insect pests, plant pathogens, nematodes, and weeds all have the ability to develop resistance quickly, even to different types of functionally similar chemistries. This phenomenon is called cross-resistance and is caused by multi-chemistry detoxification mechanisms present in many pest populations (Horowitz and Ishaaya, 2009).
Because of the increasing number of novel, low-impact chemistries available, educators and growers have additional tools to manage resistance within IPM programs (EPA, 2017a). Biopesticides have long been used in combination with synthetic chemistries to provide the basis for excellent control programs that effectively manage resistance. Additionally, they typically have modes of action that are different from synthetic pesticides and do not rely on a single target site for efficacy. Properly used, these products have the potential to extend the effective field life of all products by curtailing the development of resistant pest populations (Horowitz and Ishaaya, 2009).
According to the United States Environmental Protection Agency (EPA), “IPM is an effective and environmentally sensitive approach to pest management that relies on a combination of common-sense practices” (2017b, p. 1). The University of California Statewide Integrated Pest Management Program (UCIPM) (2017) defines the IPM approach as combining prevention, cultural, physical, biological and chemical means to control pests, all the while minimizing economic, public health, beneficial as well as non-target organism, and environmental risks. Biopesticides are noted among the low-risk and most highly effective tools for achieving crop protection in IPM systems. The challenges of farming require that IPM systems actively integrate multiple management approaches to balance optima productivity with sustainability (BPIA, 2017).
Biopesticides should be considered as a component of a holistic total program and used at an appropriate time and pest density. Today, many forward looking IPM professionals are incorporating biopesticides into traditionally conventional pest management strategies (EPA, 2017b). However, education and training are needed to address biopesticide best use practices, the methods of integrating them into IPM programs; as well as instruction to promote an understanding of their unique modes of action (EPA, 2017b). Part of the educational process involves research through fair and realistic field trials that evaluate biopesticides both as standalone treatments as well as in combination and rotation with other options with an objective of improving IPM practices (Abler et al., 1992; Kumar and Singh, 2015). All of these learning experiences are useful in demonstrating the science of biopesticide use and establishing best use practices. A better understanding of biopesticide potential and the mode of action of different active ingredients, increased grant support to promote biopesticide research, and productive grower-industry-researcher collaborations to generate applied research data and design IPM strategies are necessary to make the best use of biopesticides and for environmental sustainability.
Abler, D.G., G.P. Rauniyar, and F.M. Goode. 1992. Field trials as an extension technique: The case of Swaziland. NJARE 21(1): 30-35.
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(BPIA). Biological Products Industry Alliance. 2014. Biopesticides in a program with traditional chemicals offer growers sustainable solutions. http://www.bpia.org/wp-content/uploads/2014/01/grower-final.pdf
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(EPA). U.S. Environmental Protection Agency. 2017a. Biopesticides. https://www.epa.gov/pesticides/biopesticides#what
(EPA). U.S. Environmental Protection Agency. 2017b. Integrated pest management principles. https://www.epa.gov/safepestcontrol/integrated-pest-management-ipm-principles
Horowitz, A. and I. Ishaaya. (2009). Biorational control of arthropod pests: Application and resistance management. Springer, New York, NY.
Kumar, S., and A. Singh. 2015. Biopesticides: Present status and the future prospects. J Fertil Pestic 6: e129. doi:10.4172/2471-2728.1000e129
Osteen, C., J. Gottlieb, and U. Vasavada (eds.). 2012. Agricultural Resources and Environmental Indicators. EIB-98, U.S. Department of Agriculture, Economic Research Service, August 2012.
Popp, J., K. Peto, and J. Nagy. 2012. Pesticide productivity and food security: A review. Agron Sustain Dev 33: 243–255. DOI 10.1007/s13593-012-0105-x.
Pretty, J. and Z.P. Bharucha. 2015. Integrated pest management for sustainable intensification of agriculture in Asia and Africa. Insects 6(1): 152–182.
(UCIPM). University of California Statewide Integrated Pest Management Program. 2017. What is integrated pest management (IPM)? http://www2.ipm.ucanr.edu/WhatIsIPM/
Vallad, G.E. n.d. Use of biopesticides for the management of vegetable diseases. University of Florida Gulf Coast Research and Extension Center. http://ipm.ifas.ufl.edu/pdfs/Bio-Pesticides_Slides_IPM_site.pdf
van Zyl, S.A., J. Brink, F.J. Calitz, S. Coertze, and P.J. Fourie. 2009. The use of adjuvants to improve spray deposition and Botrytis cinerea control on Chardonnay grapevine leaves. Crop Prot 29(1): 58-67. https://doi.org/10.1016/j.cropro.2009.08.012
Wang, C.J. and Z.Q. Liu. 2007. Foliar uptake of pesticides: Present status and future challenge. Pest Biochem Phys 87(1): 1-8. https://doi.org/10.1016/j.pestbp.2006.04.004
Whitford, F., D. Penner, B. Johnson, L. Bledsoe, N. Wagoner, et al. 2009. The impact of water quality on pesticide performance. Purdue Extension Publication PPP-86. https://www.extension.purdue.edu/extmedia/ppp/ppp-86.pdf
- Author: Surendra K. Dara
Entomopathogens are microorganisms that are pathogenic to arthropods such as insects, mites, and ticks. Several species of naturally occurring bacteria, fungi, nematodes, and viruses infect a variety of arthropod pests and play an important role in their management. Some entomopathogens are mass-produced in vitro (bacteria, fungi, and nematodes) or in vivo (nematodes and viruses) and sold commercially. In some cases, they are also produced on small scale for non-commercial local use. Using entomopathogens as biopesticides in pest management is called microbial control, which can be a critical part of integrated pest management (IPM) against several pests.
Some entomopathogens have been or are being used in a classical microbial control approach where exotic microorganisms are imported and released for managing invasive pests for long-term control. The release of exotic microorganisms is highly regulated and is done by government agencies only after extensive and rigorous tests. In contrast, commercially available entomopathogens are released through inundative application methods as biopesticides and are commonly used by farmers, government agencies, and homeowners. Understanding the mode of action, ecological adaptations, host range, and dynamics of pathogen-arthropod-plant interactions is essential for successfully utilizing entomopathogen-based biopesticides for pest management in agriculture, horticulture, orchard, landscape, turf grass, and urban environments.
Important entomopathogen groups and the modes of their infection process are described below.
There are spore-forming bacterial entomopathogens such as Bacillus spp., Paenibacillus spp., and Clostridium spp, and non-spore-forming ones that belong to the genera Pseudomonas, Serratia, Yersinia, Photorhabdus, and Xenorhabdus. Infection occurs when bacteria are ingested by susceptible insect hosts. Pseudomonas, Serratia and Yersinia are not registered in the USA for insect control.Several species of the soilborne bacteria, Bacillus and Paenibacillus are pathogenic to coleopteran, dipteran, and lepidopteran insects. Bacillus thuringiensis subsp. aizawai, Bt subsp. kurstaki, Bt subsp. israelensis, Bt subsp. sphaericus, and Bt subsp. tenebrionis are effectively used for controlling different groups of target insects. For example, Bt subsp. aizawai and Bt subsp. kurstaki are effective against caterpillars, Bt subsp. israelensis and Bt subsp. sphaericus target mosquito larvae, and Bt subsp. tenebrionis is effective against some coleopterans.
When Bt is ingested, alkaline conditions in the insect gut (pH 8-11) activate the toxic protein (delta-endotoxin) that attaches to the receptors sites in the midgut and creates pore in midgut cells. This leads to the loss of osmoregulation, midgut paralysis, and cell lysis. Contents of the gut leak into insect's body cavity (hemocoel) and the blood (hemolymph) leaks into the gut disrupting the pH balance. Bacteria that enter body cavity cause septicemia and eventual death of the host insect. Insects show different kinds of responses to Bt toxins depending on the crystal proteins (delta-endotoxin), receptor sites, production of other toxins (exotoxins), and requirement of spore. The type responses below are based on the susceptibility of caterpillars to Bt toxins.
Type I response – Midgut paralysis occurs within a few minutes after delta-endotoxin is ingested. Symptoms include cessation of feeding, increase in hemolymph pH, vomiting, diarrhea, and sluggishness. General paralysis and septicemia occur in 24-48 hours resulting in the death of the insect. Examples of insects that show Type I response include silkworm, tomato hornworm, and tobacco hornworm.
Type II response – Midgut paralysis occurs within a few minutes after the ingestion of delta-endotoxin, but there will be no general paralysis. Septicemia occurs within 24-72 hours. Examples include inchworms, alfalfa caterpillar, and cabbage butterfly.
Type III response – Midgut paralysis occurs after delta-endotoxin is ingested followed by cessation of feeding. Insect may move actively as there will be no general paralysis. Mortality occurs in 48-96 hours. Higher mortality occurs if spores are ingested. Insect examples include Mediterranean flour moth, corn earworm, gypsy moth, spruce budworm.
Type IV response – Insects are naturally resistant to infection and older instars are less susceptible than the younger ones. Midgut paralysis occurs after delta-endotoxin is ingested followed by cessation of feeding. Insect may move actively as there will be no general paralysis. Mortality occurs in 72-96 or more hours. Higher mortality occurs if spores are ingested. Cutworms and armyworms are examples for this category.
Unlike caterpillars, the response in mosquitoes is different where upon ingestion of Bt subsp. israelensis delta-endotoxin, the mosquito larva is killed within 20-30 min.
While Bt with its toxic proteins is very effective as a biopesticide against several pests, excessive use can lead to resistance development. Corn earworm, diamondback moth, and tobacco budworm are some of the insects that developed resistance to Bt toxins. Genetic engineering allowed genes that express Bt toxins to be inserted into plants such as corn, cotton, eggplant, potato, and soybean and reduced the need to spray pesticides. However, appropriate management strategies are necessary to reduce insect resistant to Bt toxins in transgenic plants.
Paenibacillus popilliae is commonly used against Japanese beetle larvae and known to cause the milky spore disease. Although Serratia is not registered for use in the USA, a species is registered for use against a pasture insect in New Zealand. In the case of Photorhabdus spp. and Xenorhabdus spp., which live in entomopathogenic nematodes symbiotically, bacteria gain entry into the insect host through nematodes. Biopesticides based on heat-killed Chromobacterium subtsugae and Burkholderia rinojensis are reported to have multiple modes of action and target mite and insect pests of different orders.
Entomopathogenic fungi typically cause infection when spores come in contact with the arthropod host. Under ideal conditions of moderate temperatures and high relative humidity, fungal spores germinate and breach the insect cuticle through enzymatic degradation and mechanical pressure to gain entry into the insect body. Once inside the body, the fungi multiply, invade the insect tissues, emerge from the dead insect, and produce more spores. Natural epizootics of entomophthoralean fungi such as Entomophaga maimaiga (in gypsy moth), Entomophthora muscae (in flies), Neozygites fresenii (in aphids), N. floridana (in mites), and Pandora neoaphidis (in aphids) are known to cause significant reductions in host populations. Although these fastidious fungi are difficult to culture in artificial media and do not have the potential to be sold as biopesticides they are still important in natural control of some pest species. Hypoclealean fungi such as Beauveria bassiana, Isaria fumosorosea, Hirsutella thompsonii, Lecanicillium lecanii, Metarhizium acridum, M. anisopliae, and M. brunneum, on the other hand, are commercially sold as biopesticides in multiple formulations around the world. Fungal pathogens have a broad host range and are especially suitable for controlling pests that have piercing and sucking mouthparts because spores do not have to be ingested. However, entomopathogenic fungi are also effective against a variety of pests such as wireworms and borers that have chewing mouthparts.
Related to fungi, the spore-forming microsporidium, Paranosema (Nosema) locustae is a pathogen that has been used for controlling locusts, grasshoppers, and some crickets. When P. locustae is ingested, the midgut tissues become infected, followed by infection in the fat body tissues. The disease weakens and eventually kills the orthopteran host within a few weeks.
Entomopathogenic nematodes are microscopic, soil-dwelling worms that are parasitic to insects. Several species of Heterorhabditis and Steinernema are available in multiple commercial formulations, primarily for managing soil insect pests. Infective juveniles of entomopathogenic nematodes actively seek out their hosts and enter through natural openings such as the mouth, spiracles, and anus or the intersegmental membrane. Once inside the host body, the nematodes release symbiotic bacteria that kill the host through bacterial septicemia. Heterorhabditis spp. carry Photorhabdus spp. bacteria and Steinernema spp. carry Xenorhabdus spp. bacteria. Phasmarhabditis hermaphrodita is also available for controlling slugs in Europe, but not in the USA.
Infective juvenile of Steinernema carpocapsae entering the first instar larva of a leafminer through its anus.
Similar to bacteria, entomopathogenic viruses need to be ingested by the insect host and therefore are ideal for controlling pests that have chewing mouthparts. Several lepidopteran pests are important hosts of baculoviruses including nucleopolyhedroviruses (NPV) and granuloviruses (GV). These related viruses have different types of inclusion bodies in which the virus particles (virions) are embedded. Virus particles invade the nucleus of the midgut, fat body or other tissue cells, compromising the integrity of the tissues and liquefying the cadavers. Before death, infected larvae climb higher in the plant canopy, which aids in the dissemination of virus particles from the cadavers to the lower parts of the canopy. This behavior aids in the spread of the virus to cause infection in healthy larvae. Viruses are very host specific and can cause significant reduction of host populations. Examples of some commercially available viruses include Helicoverpa zea single-enveloped nucleopolyhedrovirus (HzSNVP), Spodoptera exigua multi-enveloped nucleopolyhedrovirus (SeMNPV), and Cydia pomonella granulovirus (CpGV).
Most entomopathogens typically take 2-3 days to infect or kill their host except for viruses and P. locustae which take longer. Compared to viruses (highly host specific) and bacteria (moderately host specific), fungi generally have a broader host range and can infect both underground and aboveground pests. Because of the soil-dwelling nature, nematodes are more suitable for managing soil pests or those that have soil inhabiting life stages.
Microbial control and Integrated Pest Management
There are several examples of entomopathogen-based biopesticides that have played a critical role in pest management. Significant reduction in tomato leaf miner, Tuta absoluta, numbers and associated yield loss was achieved by Bt formulations in Spain (Gonzalez-Cabrera et al, 2011). Bt formulations are also recommended for managing a variety of lepidopteran pests on blueberry, grape, and strawberry (Haviland, 2014; Zalom et al, 2014; Bolda and Bettiga, 2014; Varela et al, 2015).
Lecanicellium muscarium-based formulation reducedgreenhouse whitefly (Trialeurodes vaporariorum) populations by 76-96% in Mediterranean greenhouse tomato (Fargues et al, 2005). In other studies, B. bassiana applications resulted in a 93% control of twospotted spider mite (Tetranychus urticae) populations in greenhouse tomato (Chandler et al, 2005) and 60-86% control on different vegetables (Gatarayiha et al, 2010). The combination of B. bassiana and azadirachtin reduced rice root aphid (Rhopalosiphum rufiabdominale) and honeysuckle aphid (Hyadaphis foeniculi) populations by 62% in organic celery in California (Dara, 2015a). Chromobacterium subtsugae and B. rinojensis caused a 29 and 24% reduction, respectively, in the same study. IPM studies in California strawberries also demonstrated the potential of entomopathogenic fungi for managing the western tarnished plant bug (Lygus hesperus) and other insect pests (Dara, 2015b, 2016). Entomopathogenic fungi also have a positive effect on promoting drought tolerance or plant growth as seen in cabbage (Dara et al, 2016) and strawberry (Dara, 2013) and antagonizing plant pathogens (Dara et al, 2017)
Application of SeMNPV was as efficacious as methomyl and permithrin in reducing beet armyworms (S. exigua) in head lettuce in California (Gelernter et al, 1986). Several studies demonstrated PhopGV as an important tool for managing the potato tubermoth (Phthorimaea operculella) (Lacey and Kroschel, 2009).
The entomopathogenic nematode, S. feltiae,reduced raspberry crown borer (Pennisetia marginata) populations by 33-67% (Capinera et al, 1986). For managing the branch and twig borer (Melagus confertus) in California grapes, S. carpocapsae is one of the recommended options (Valera et al, 2015).
Entomopathogens can be important tools in IPM strategies in both organic and conventional production systems. Depending on the crop, pest, and environmental conditions, entomopathogens can be used alone or in combination with chemical, botanical pesticides or other entomopathogens.
Acknowledgements: Thanks to Dr. Harry Kaya for reviewing this article.
Bolda, M. P. and L. J. Bettiga. 2015. UC IPM Pest Management Guidelines: Caneberries. UC ANR Pub. 3437.
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- Author: Surendra K. Dara
Arthropod pests or diseases cause a variety of damages to crops. Some by reducing plant vigor resulting in lesser yields and some by causing direct damage to the produce which can be unmarketable due to deformity, unpleasant taste, damaged tissue due to insect feeding, presence of insects and/or frass, decay due to secondary infections, and other factors. It is quite understandable when the produce is not accepted because of the taste or potential health risk. For example, citrus fruit with huanglongbing or citrus greening disease transmitted by Asian citrus psyllid gives a bitter taste to citrus juice. Navel orangeworm larvae bore into almonds and feed on the nut causing complete or partial damage and leave frass and cause fungal infections. Brown marmorated stink bug damage on fruits and vegetables change the texture and taste of the damaged area. Such damage certainly makes the produce unmarketable and applying pesticides or administering other control measures to prevent the damage is warranted.
On the other hand, certain damage is only cosmetic with no reported change in taste or quality of the produce. One example would be fruit deformity caused by the lygus bug in strawberries. Strawberry is a high value fruit appreciated for its taste, shape, color, and flavor. Lygus bug feeding on young green berries results in uneven growth and deformity of mature berries. While there is no record of the impact of lygus damage on strawberry fruit quality, millions of pounds of pesticides are applied to control lygus bug or similar pests that cause cosmetic damage in strawberries and other crops.
The preference of consumers for perfectly shaped fruits and vegetables creates a need for intensive pest management practices and results in associated financial and environmental costs. Since chemical pesticides are generally economical and effective tools to manage pests, they are widely used. The overuse of certain effective pesticides causes development of resistance in pest populations. This, in turn, leads to increased use of the same or other pesticides. Excessive use of chemical pesticides can have a harmful effect on beneficial arthropods resulting in secondary pest outbreaks. Organic agriculture is gaining popularity due to environmental and human health concerns from chemical pesticide use. “Organic agriculture produces products using methods that preserve the environment and avoid most synthetic materials, such as pesticides and antibiotics” according to USDA. But organic agriculture is not necessarily the only sustainable solution.
Before agricultural industrialization, there was a better balance between pests and their natural enemies (beneficial arthropods such as predators and parasitoids that attack pests). Once agriculture was industrialized, thousands of acres of monoculture now provide an unlimited supply of food for a variety of pests. When the natural balance is disrupted, natural enemies alone are not sufficient to manage pest populations. This is where an Integrated Pest Management (IPM) strategy plays an important role in bringing a sense of balance into pest management. IPM employs multiple tools that include selecting resistant varieties, modifying planting dates, changing irrigation and nutrient management practices, conserving or releasing natural enemies, applying chemical, botanical, and microbial pesticides, or using mechanical tools. Each of these tools contribute to reducing pest numbers, complement each other, and result in pest management in an environmentally sustainable manner.
Organic agriculture, on the other hand, relies on biopesticides instead of chemical pesticides, which can sometimes be less effective or slow in achieving desired control. For example, an effective chemical pesticide with a specific mode of action could kill pest populations within a few hours of application. However, using a biopesticide based on an insect-pathogenic microorganism like the bacterium Bacillus thuringiensis or the fungus Beauveria bassiana, can take a few days to allow the microorganism to infect and kill the pest. When pest numbers are low, non-chemical solutions may provide required control to minimize damage. However, with heavy pest infestations, chemical pesticides are often needed to provide timely control that prevents further buildup of pest populations and the resulting damage to crops.
Organic agriculture is expensive because of generally higher losses due to pests and higher cost of agronomic and pest management practices. Sometimes, ineffective control of pests on organic farms may result in their spread to neighboring fields and increase the risk of pest damage. Organic agriculture does not mean pesticide-free farming, and biopesticides used on organic farms also require safety guidelines similar to chemical pesticides used on conventional farms. Organic agriculture may require a higher number of pesticide sprays increasing the risk of exposure for workers. In some pest and disease situations in certain crops, organically registered products are not available and yield losses could be higher. Exporting organic produce, in light of exotic and invasive pests spreading to other areas, is also a challenge due to limited options for shipping organically produced pest-free fruits and vegetables.
Using cultural practices to reduce the risk of pest infestations and applying biopesticides when pest populations are low and chemical pesticides when populations are high can be components of an IPM strategy where multiple tools are exploited in a balanced manner. Combining and rotating chemical pesticides with non-chemical alternatives strengthens the effectiveness of IPM by providing desired control without the excessive use of chemicals. Chemical pesticides can be used during early stages of the crop growth while biopesticides can be used closer to harvest.
Considering the challenges and risks associated with organic agriculture and the practicality of IPM-based agriculture, a couple of ideas could be worth pursuing to maintain environmental and human health, reduce harmful chemicals, and ensure food security for the growing world population.
Acceptance of imperfect produce: When consumers are tolerant of imperfectly shaped fruits and vegetables with no health risk from pathogens or arthropod pests, a significant amount of pesticides of all kinds could be avoided. This would translate into saving millions of dollars otherwise spent on pesticides and their application costs, and money earned on selling otherwise unmarketable produce. This may also reduce the disposal of unpicked produce at the grocery stores. When consumers accept imperfect fruits or vegetables, the cost of produce, both to produce and purchase, could come down. I recently came across Imperfect Produce, a company that sells imperfect produce and End Food Waste, an organization that started the Ugly Fruit And Veg Campaign.
IPM: Considering the difficulty in ensuring food security exclusively through non-chemical agriculture for the growing world population (projected to be 9.6 billion by 2050), IPM is an effective, practical, and sustainable tool that uses a balanced approach. While organic agriculture is encouraged and supported, and there are several organizations that certify organic production around the world, IPM hasn't caught the attention of marketers yet. Perhaps a seal of IPM should be considered and promoted in the near future.
Opinions expressed in this article are my own and based on my experience in IPM, microbial control, biological control, and from discussions with several growers and scientists.