3

Applying Agroecological Concepts to Development of Ecologically Based Pest Management Strategies

MIGUEL A. ALTIERI and CLARA INES NICHOLLS

University of California, Berkeley

Most scientists today would agree that conventional modern agriculture faces an environmental crisis. Serious problems such as land degradation, salinization, pesticide pollution of soil, water, and food chains, depletion of ground water, genetic homogeneity, and associated vulnerability raise serious questions regarding the sustainability of modern agriculture. The causes of the environmental crisis are rooted in the prevalent socioeconomic system, which promotes monocultures and the use of high input technologies, and agricultural practices that lead to natural resource degradation. Such degradation is not only an ecological process but also a social, political, and economic process. While productivity issues represent part of the problem of natural resource degradation, addressing the problem of agricultural production must go beyond technological issues and include attention to social, cultural, and economic issues that account for the crisis as well.

The loss of yields due to pests in many crops, despite the substantial increase in the use of pesticides, is a symptom of the environmental crisis affecting agriculture. It is well known that cultivated plants grown in genetically homogeneous monocultures do not possess the necessary ecological defense mechanisms to tolerate pest populations that experience outbreaks. Modern agriculturists have selected crops for high yields and high palatability, making them more susceptible to pests by sacrificing natural resistance for productivity. On the other hand, modern agricultural practices negatively affect pests ' natural



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 14
PROFESSIONAL SOCIETIES and Ecologically Based Pest Management: Proceedings of a Workshop 3 Applying Agroecological Concepts to Development of Ecologically Based Pest Management Strategies MIGUEL A. ALTIERI and CLARA INES NICHOLLS University of California, Berkeley Most scientists today would agree that conventional modern agriculture faces an environmental crisis. Serious problems such as land degradation, salinization, pesticide pollution of soil, water, and food chains, depletion of ground water, genetic homogeneity, and associated vulnerability raise serious questions regarding the sustainability of modern agriculture. The causes of the environmental crisis are rooted in the prevalent socioeconomic system, which promotes monocultures and the use of high input technologies, and agricultural practices that lead to natural resource degradation. Such degradation is not only an ecological process but also a social, political, and economic process. While productivity issues represent part of the problem of natural resource degradation, addressing the problem of agricultural production must go beyond technological issues and include attention to social, cultural, and economic issues that account for the crisis as well. The loss of yields due to pests in many crops, despite the substantial increase in the use of pesticides, is a symptom of the environmental crisis affecting agriculture. It is well known that cultivated plants grown in genetically homogeneous monocultures do not possess the necessary ecological defense mechanisms to tolerate pest populations that experience outbreaks. Modern agriculturists have selected crops for high yields and high palatability, making them more susceptible to pests by sacrificing natural resistance for productivity. On the other hand, modern agricultural practices negatively affect pests ' natural

OCR for page 14
PROFESSIONAL SOCIETIES and Ecologically Based Pest Management: Proceedings of a Workshop enemies, which in turn do not find the necessary environmental resources and opportunities in monocultures to effectively suppress pests. As long as the structure of monocultures is maintained as the structural base of agricultural systems, pest problems will continue to persist. Thus, the major challenge for those advocating ecologically based pest management (EBPM) is to find strategies to overcome the ecological limits imposed by monocultures. Integrated pest management (IPM) approaches have not addressed the ecological causes of the environmental problems in modern agriculture. There still prevails a narrow view that specific causes affect productivity, and overcoming the limiting factor (e.g., insect pest) via new technologies continues to be the main goal. In many IPM projects the main focus has been to substitute less noxious inputs for the agrochemicals that are blamed for so many of the problems associated with conventional agriculture. Emphasis is now placed on purchased biological inputs such as Bacillus thuringiensis, a microbial pesticide that is now widely applied in place of chemical insecticide. This type of technology pertains to a dominant technical approach called input substitution. The thrust is highly technological, characterized by a limiting factor mentality that has driven conventional agricultural research in the past. Agronomists and other agricultural scientists have for generations been taught the “law of the minimum ” as a central dogma. According to this dogma, at any given moment there is a single factor limiting yield increases, and that factor can be overcome with an appropriate external input. Once one limiting factor has been surpassed—for example nitrogen deficiency, with urea as the correct input—then yields may rise until another factor, pests for example, becomes the new limiting factor due to increased levels of free nitrogen in the foliage that attracts and supports the herbivore populations. That factor then requires another input— a pesticide in this case—and so on, perpetuating a process of treating symptoms rather than dealing with the real causes that evoked the ecological imbalance. The addition of biotechnology-based approaches in pest management is merely a new tool to be used as input substitutions to address the problems (e.g., pesticide resistance, pollution, soil degradation) caused by previous agrochemical technologies. Transgenic crops developed for pest control closely follow the paradigm of using a single control mechanism (a pesticide) that, as a strategy, has been shown to fail repeatedly over time against pest insects, pathogens, and weeds. Transgenic crops are likely to increase the use of pesticides and to accelerate the evolution of “super weeds” and resistant insect pests. The “one gene–one pest” approach emphasized by plant breeders introducing vertical resistance or by biotechnologists developing transgenic crops has proven to be easily overcome by pests that are continuously adapting to new situations and evolving detoxification mechanisms. There are many unanswered ecological questions regarding the impact of the release of transgenic plants and microorganisms into the environment. Among the major environmental risks associated with genetically engineered plants are the unintended transfer to plant relatives of the “transgenes ” and the unpredictable ecological effects.

OCR for page 14
PROFESSIONAL SOCIETIES and Ecologically Based Pest Management: Proceedings of a Workshop Given the above considerations, agroecological theory predicts that biotechnology will exacerbate the problems of conventional agriculture. By promoting monocultures it will also undermine ecological practices of farming, such as crop rotation and polycultures, which are key strategies to break the homogeneous nature of monocultures. As presently conceived, biotechnology does not fit into the broad ideals of sustainable agriculture. This production-oriented viewpoint has diverted agriculturists from realizing that limiting factors only represent symptoms of a more systematic disease inherent to imbalances within the agroecosystem. This viewpoint has also diverted them from an appreciation of the complexity of agroecological processes, thus underestimating the root causes of agricultural limitations. A useful framework to achieve a deeper knowledge of the dynamics of agroecosystems is to use agroecological principles. Agroecology goes beyond a one-dimensional view of agroecosystems and includes their genetics, agronomy, and edaphology in order to embrace an understanding of ecological and social levels of coevolution, structure, and function. For agroecologists, sustainable yield in the agroecosystem derives from the proper balance of crops, soils, nutrients, sunlight, moisture, and other coexisting organisms. The agroecosystem is productive and healthy when these balanced and rich growing conditions prevail and when crop plants remain resilient to tolerate stress and adversity. Occasional disturbances can be overcome by a vigorous agroecosystem that is adaptable and diverse enough to recover once the stress has passed. Occasionally strong measures (e.g., microbial insecticides, alternative fertilizers) may need to be applied by farmers employing alternative methods to control specific pests or soil problems. Agroecology provides the guidelines to carefully manage agroecosystems without unnecessary or irreparable damage. Simultaneous with the struggle to fight pests or diseases, the agroecologist strives to restore the resiliency and health of the agroecosystem. If the cause of disease or pests and so forth is recognized as an imbalance, then the goal of the agroecological treatment is to recover the balance. In agroecology, biodiversification is the primary technique to evoke self-regulation and sustainability. From a management perspective, the agroecological objective is to provide a balanced environment, sustained yields, biologically mediated soil fertility, and natural pest regulation through the design of diversified agroecosystems and the use of low-input technologies. The strategy is based on ecological principles that lead crop management to optimal recycling of nutrients and organic matter turnover, closed energy flows, water and soil conservation, and a balance between pest and natural enemy populations. The strategy exploits the complementary and synergistic attributes that result from the various combinations of crops, trees, and animals in spatial and temporal arrangements. These combinations determine the establishment of a planned and associated functional biodiversity, which performs key ecological services in the agroecosystem. The optimal behavior of agroecosystems depends on the level of interactions between and among the various biotic and abiotic components. By assembling a functional biodiversity, it is possible to initiate synergistic

OCR for page 14
PROFESSIONAL SOCIETIES and Ecologically Based Pest Management: Proceedings of a Workshop responses that subsidize agroecosystem processes by providing ecological services, such as the activation of soil biology, the recycling of nutrients, the enhancement of beneficial arthropods and antagonists, and so on. In other words, ecological concepts are utilized to favor natural processes and biological interactions that optimize synergies so that diversified farms are able to sponsor their own soil fertility, crop protection, and productivity. By assembling crops, animals, trees, soils, and other factors in spatially and or temporally diversified schemes, several processes are optimized. Such processes (such as organic matter accumulation, nutrient cycling, natural control mechanisms, etc.) are crucial in determining the sustainability of agricultural systems. Agroecology takes greater advantage of natural processes and beneficial on-farm interactions in order to reduce off-farm input use and to improve the efficiency of farming systems. Technologies emphasized tend to enhance the functional biodiversity of agroecosystems as well as the conservation of existing on-farm resources. Promoted technologies are multifunctional, as their adoption usually means favorable changes in various components of the farming systems at the same time. For example, legume-based crop rotations are one of the simplest forms of biodiversification and can simultaneously optimize soil fertility and pest regulation. It is well known that rotations improve yields by the known action of interrupting weed, disease, and insect life cycles. However, they can also have subtle effects such as enhancing the growth and activity of soil organisms, including vesicular arbuscular mycorrhizae, which allow crops to more efficiently use soil nutrients and water. Another practice is cover cropping or the growing of pure or mixed stands of legumes and cereals to protect the soil against erosion, which ameliorates soil structure, enhances soil fertility, and suppresses pests including weeds, insects, and pathogens. Cover crops can improve soil structure and water penetration, prevent soil erosion, modify the microclimate, and reduce weed competition. Besides these effects, cover crops can affect the dynamics of orchards and vineyards by enhancing soil biology and fertility and by increasing the biological control of insect pest populations through the harboring of predators and parasites. Perhaps the most dramatic example of the integrative effects of a multipurpose technology in simultaneously enhancing IPM and soil fertility is organic soil management. Some studies suggest the physiological susceptibility of crops to insects is affected by the form of fertilizer used (organic vs. chemical fertilizer). Studies documenting lower density of several insect herbivores in low-input farming systems have partly attributed such reduction to lower nitrogen content in the organically farmed crops. The ultimate goal of agroecological design is to integrate components so that overall biological efficiency is improved, biodiversity is preserved, and the agroecosystem productivity and its self-sustaining capacity is maintained. The goal is to design an agroecosystem that mimics the structure and function of natural ecosystems. These systems typically include:

OCR for page 14
PROFESSIONAL SOCIETIES and Ecologically Based Pest Management: Proceedings of a Workshop Vegetative cover as an effective soil- and water-conserving measure, met through the use of no-till practices, mulch farming, and cover crops and other appropriate methods; Regular supply of organic matter through the addition of organic matter (manure and compost) that results in the promotion of soil biotic activity; Nutrient recycling mechanisms through the use of crop rotations and crop/livestock systems based on the use of legumes; and Pest regulation assured through enhanced activity of biological control agents achieved by introducing and/or conserving natural enemies and antagonists. The process of converting a conventional crop production system that relies heavily on systemic, petroleum-based inputs to a diversified agroecosystem with low inputs is not simply a process of withdrawing external inputs without compensatory replacement or alternative management. Considerable ecological knowledge is required to direct the array of natural flows necessary to sustain yields in a low-input system. The process of conversion from a high-input conventional management to a low-external-input management is a transitional process with four marked phases: progressive chemical withdrawal; rationalization and efficiency of agrochemical use through integrated pest management and integrated nutrient management; input substitution—using alternative, low-energy input technologies; and redesign of diversified farming systems with an optimal crop/animal integration, which encourages synergism so that the system can sponsor its own soil fertility, natural pest regulation, and crop productivity. During the four phases, management is guided to ensure the following processes: increasing biodiversity both in the soil and above ground; increasing biomass production and soil organic matter content; decreasing levels of pesticide residues and losses of nutrients and water components; establishment of functional relationships between the various plant and animal components on the farm; and optimal planning of crop sequences and combinations and efficient use of locally available resources. The challenge for EBPM scientists is to identify the correct management techniques and crop assemblages that, through their biological synergism, will provide key ecological services that sustain the performance of agroecosystems. The exploitation of these synergisms in real farm settings involves agroecosystem design and management that require an understanding of the numerous relationships among soils, plants, herbivores, and natural enemies. Clearly, the emphasis of this approach is to restore natural control mechanisms

OCR for page 14
PROFESSIONAL SOCIETIES and Ecologically Based Pest Management: Proceedings of a Workshop through the addition of selective biodiversity components within and outside the crop field, thereby creating a whole array of possible arrangements of vegetation in time and space.