A variety of management implications of our understanding of pest population dynamics have been presented in previous sections. However, it is important to take a broader perspective and consider how all the different tools at the pest controller's disposal can be deployed most effectively, both to maximize the economic benefit of reducing pest density and to minimize the adverse environmental and health consequences. This is what integrated pest management (IPM) is intended to achieve. It combines physical control (for example, simply keeping invaders from arriving, keeping pests away from crops, or picking them off by hand when they arrive), cultural control (for example, rotating the crops planted in a field so pests cannot build up their numbers over several years), biological and chemical control, and the use of resistant varieties of crop. IPM came of age as part of the reaction against the unthinking use of chemical pesticides in the 1940s and 1950s.
IPM is ecologically based and relies heavily on natural mortality factors, such as weather and enemies, and seeks to disrupt the latter as little as possible. It aims to control pests below the EIL, and it depends on monitoring the abundance of pests and their natural enemies and using various control methods as complementary parts of an overall program. Broad-spectrum pesticides in particular, although not excluded, are used only very sparingly, and if chemicals are used at all it is in ways that minimize the costs and quantities used. The essence of the IPM approach is to make the control measures fit the pest problem, and no two problems are the same - even in adjacent fields. Thus, IPM often involves the development of computer-based expert systems inoculation against glasshouse pests microbial control of insects via inundation biological control is not always environmentally friendly
IPM: an ecologically rather than chemically based philosophy k
Growth stage of crop?
Time of year?
Possible to use cultural controls?
If not possible that can be used by farmers to diagnose pest problems and suggest appropriate responses (Mahaman et al., 2003).
The caterpillar of the potato tuber moth (Phthorimaea operculella) commonly damages crops in New Zealand. An invader from a warm temperate subtropical country, it is most devastating when conditions are warm and dry (i.e. when the environment coincides closely with its optimal niche requirements - see Chapter 3). There can be as many as 6-8 generations per year and different generations mine leaves, stems and tubers. The caterpillars are protected both from natural enemies (parasitoids) and insecticides when in the tuber, so control must be applied to the leaf-mining generations. The IPM strategy for potato tuber moth (Herman, 2000) involves: (i) monitoring (female pheromone traps, set weekly from mid summer, are used to attract males, which are counted); (ii) cultural methods (the soil is cultivated to prevent soil cracking, soil ridges are molded up more than once and soil moisture is maintained); and (iii) the use of insecticides, but only when absolutely necessary (most commonly the organophosphate, methamidophos). Farmers follow the decision tree shown in Figure 15.5.
Implicit in the philosophy of IPM is the idea that pest control cannot be isolated from other aspects of food production and it is especially bound up with the means by which soil fertility is maintained and improved. These broader sustainable agricultural systems, including IFS (integrated farming systems) in the USA and LIFE (lower input farming and environment) in Europe (International Organisation for Biological Control, 1989; National Research Council, 1990), have advantages in terms of reduced environmental hazards. Even so, it is unreasonable to suppose that they will be adopted widely unless they are also sound in economic terms. In this context, Figure 15.6 shows the yields of apples from organic, conventional and integrated production systems in Washington State from 1994 to 1999 (Reganold et al., 2001).
Figure 15.5 Decision flow chart for the integrated pest management of potato tuber moths (PTM) in New Zealand. Boxed phrases are questions (e.g. 'what is the growth stage of the crop?'), the words in the arrows are the farmer's answers to the questions (e.g. 'before the tuber has formed') and the recommended action is shown in the vertical box ('don't spray the crop'). Note that February is late summer in New Zealand. (After Herman, 2000.) Photograph © International Potato Center (CIP).
1997 1998 Year
IPM for the potato tuber moth integration of IPM in sustainable farming systems
Figure 15.6 The fruit yields of three apple production systems. (From Reganold et al., 2001.)
Organic management excludes such conventional inputs as synthetic pesticides and fertilizers whilst integrated farming uses reduced amounts of chemicals by integrating organic and conventional approaches. All three systems gave similar apple yields but the organic and integrated systems had higher soil quality and potentially lower environmental impacts. When compared with conventional and integrated systems, the organic system produced sweeter apples, higher profitability and greater energy efficiency. Note, however, that despite some widely held beliefs, organic farming is not totally free of adverse environmental consequences. For example, some approved pesticides are just as harmful as synthetic ones whilst the application of animal manure may lead to undesirable levels of nitrate runoff to streams just as synthetic fertilizers can (Trewavas, 2001). There is a need for research to compare the types and magnitudes of environmental consequences of the various approaches to agricultural management.
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