Insect Pest Management: Differences Between Conventional and Organic Farming Systems

Integrated Pest Management (IPM), as defined by the United States Environmental Protection Agency (2007), is "the coordinated use of pest and environmental information with available pest control methods to prevent unacceptable levels of pest damage by the most economical means and with the least possible hazard to people, property, and the environment." For nonorganic farming systems, extensive information is available, through land-grant university Cooperative Extension services and other sources, about Integrated Pest Management (IPM) and control of insect pests. Although much of the basic information about insect pest biology is broadly useful, some important differences in approaches to IPM between nonorganic and organic farming systems should be noted.

IPM and the 'Economic Injury Level' Concept

The basic goal of IPM is to control populations of pests so as to minimize economic losses resulting from their damage. A key concept used for decision making in IPM is the concept of the Economic Injury Level (EIL). This concept was first introduced by Stern et al. (1959), who defined it as “The lowest population density of a pest that will cause economic damage; or the amount of pest injury which will justify the cost of control.” IPM decision-making—whether or not to take action to suppress a pest population—in nonorganic systems is dependent on this concept. The EIL is usually expressed as a pest density, but actually it is a level of injury that is indexed by pest numbers. Insect numbers (counts) are used because they typically correlate well with injury—both current and future—and it is often easier to count insects than to quantify injury. Because the results of control measures against insect pests are delayed somewhat after the detection of economically damaging populations, a second concept important to IPM decision-making is required: the Economic Threshold. The Economic Threshold (ET) is the pest abundance at which the EIL is likely to be equalled or exceeded unless the decision to implement control measures is taken; it typically occurs at a pest abundance below the EIL. Pest abundances or injury levels that reach the ET trigger the implementation of reactive control measures because those populations are predicted to result in economic losses if not controlled, whereas pest abundances or injury levels below the ET do not merit intervention. These concepts are illustrated in Fig. 1.

Figure 1. The Economic Injury Level (EIL) is the pest abundance (or level of damage) at which the dollar cost of crop yield loss to the pest begins to exceed the dollar cost of controlling the pest. The Economic Threshold (ET) is the pest abundance (or damage level) at which the EIL is likely to be equalled or exceeded if left unmanaged. The ET is almost always lower than the EIL, and is considered to be the point at which action against the pest is economically justified. The ET is sometimes called an Action Threshold (AT). Figure credit: Ed Zaborski, University of Illinois.

Assumptions Behind Use of the Economic Injury Level Concept in IPM

There are many assumptions about the farming and marketing system built into the EIL and ET concepts that can affect the ability of an organic producer to adopt IPM programs developed for nonorganic farming systems. These assumptions include: cost and availability of allowable, effective control materials, and the market value of the crop.

Cost and availability of allowable, effective control materials

The success of IPM in nonorganic farming systems is often due to a ready arsenal of efficacious synthetic chemical pesticides. Indeed, many of the IPM systems developed for nonorganic crops are based on the preemptive use of pest control materials, such as genetically-modified crops and insecticidal seed treatments, or assessment of pest populations and control of them with the use of “therapeutic” materials (chemical or biological) in a timely, but reactive way. In comparison to conventional systems, the numbers of allowable materials that can be used in a reactive way in organic systems is extremely limited. Often, information on the efficacy of a material allowable in organic systems for a specific pest is lacking. The cost of some allowable materials can be quite high. Therefore, even if an allowable, efficacious pest control material is available, its cost may exceed the benefit that might be gained in using it.

Keep in mind that the National Organic Program (NOP) final rule (United States Deptartment of Agriculture [USDA], 2000) requires that organic farm managers employ preventive management practices to reduce the possibility of weed, insect, and disease problems, and to use nontoxic biological, physical, and mechanical methods to reactively manage pest problems if they do occur. Only when these practices are insufficient to prevent or control pests can organically-approved pesticidal materials be used in Certified Organic farming systems. (Caution: the use of an unapproved material can result in the loss of certification. Always check with your certifier before purchasing or using a new product or material to ensure that it is permitted for use in your organic farming system. For more information, read the related article, Can I Use This Input On My Organic Farm?)

The logical application of the EIL and ET concepts is not limited, however, to the application of pesticidal materials. The appropriate use of any reactive measure to suppress pest populations or their injury to crops—including the nontoxic biological, physical, and mechanical methods that organic farm managers are required to employ in response to an emerging pest problem—could be guided by properly established EILs and ETs. These reactive measures might involve, for example, running a 'bug vaccuum' over a lettuce crop to control leaf hoppers, releasing parasites or predators in a greenhouse to control aphids, or even handpicking hornworms off of tomato plants; all of these incur costs to the grower and may not be justified at lower levels of pest abundance or injury. The use of EILs and ETs would help ensure that the use of these measures was economically justifiable. Unfortunately, limited science-based information about the true costs and efficacy for many of these control measures—information necessary for the development of reliable EILs and ETs—is available for many crops and regions.

Market value of the crop

Organic crops often have a higher market value than the same crop produced nonorganically. Additionally, market channel can also affect the value of a crop and the acceptance of damage. For example, crops sold through wholesale channels for use in processing may have a lower unit value, and have different cosmetic quality requirements than those sold through direct market channels.

The Organic Systems Plan and IPM

Finally, the NOP final rule (USDA, 2000) requires that the manager of a certified organic farm describe explicitly, in the Organic Systems Plan, how the organic farming system will be designed so that pests: do not find plants (cultural and physical control); or are controlled by natural enemies (biological control). Vigorous, healthy plants are more able to withstand damage caused by arthropods and disease. Therefore, a “plant positive” (as opposed to “pest negative”) approach of managing the system for beneficial processes and cycles and creating healthy soil and plants, is the foundation upon which integrated pest management in successful organic production systems is built.

References and Citations

• Stern, V. M., R. F. Smith, R. van den Bosch, and K. S. Hagen. 1959. The integrated control concept. Hilgardia 29: 81–101.
• United States Department of Agriculture. 2000. National organic program: Final rule. Codified at 7 C.F.R., part 205. (Available online at: http://www.ecfr.gov/cgi-bin/text-idx?SID=a6a0935ddf00e166695f4c2138bd58d8&mc=true&node=pt7.3.205&rgn=div5) (verified 15 March 2010).
• United States Environmental Protection Agency. 2007. Pesticides and food: What "Integrated Pest Management" means [Online]. Available at http://www.epa.gov/pesticides/food/ipm.htm (verified 15 March 2010).

Additional Resources

• Pedigo, L. P. Economic thresholds and economic injury levels [Online]. In: E. B. Radcliffe,W. D. Hutchison & R. E. Cancelado (ed.) Radcliffe's IPM world textbook. University of Minnesota, St. Paul, MN. Available at: http://ipmworld.umn.edu/pedigo (verified 5 Nov 2015).