**4. Decision making in IPM**

**3. Systems in agriculture and the situation of IPM as a sub-system**

therefore, to only some of the inputs [45].

236 Soybean - Pest Resistance

**Figure 1.** A hierarchy of systems in agriculture

Spedding [44] defined a system as a group of interacting components, operating together for a common purpose, capable of reaching as a whole to external stimuli. A system is unaffected by its own output and has a specified boundary based on the inclusion of all significant feedbacks. However, four types of systems are generally acknowledged in ag‐ riculture including ecosystem, agroecosystem, farming systems and cropping systems (Figure 1). In this hierarchy, a system may consist of several sub-systems. IPM is a subsystem of cropping system and considered as the operating system used by farmers to manage population of crop pests. This sub-system has a degree of independence and can be studied in isolation of the cropping system. It has its own inputs and has the same output as the main system (i. e. yield) but relates to only some of the components and

> Following widespread concerns about the adverse effects of insecticides it became clear that calendar spraying was not the appropriate approach to pest control. In fact, determining whether an insect control measure (usually an insecticide) is "needed" is one of the basic principles of any IPM programme. "Need" can be defined in a number of ways, but most growers associate the need for an insecticide with economics. In other words, most growers ask some form of these questions: "How many insects cause how much damage?", "Are the damage levels all significant?" and "Will the value of yield protection with an insecticide offset the cost of control?" Therefore, researchers from different agricultural disciplines came to realize that a decision rule or threshold should answer such questions and that pest control must be viewed as a decision making process (Figure 2).

> Pest management is a combination of processes that include obtaining the information, deci‐ sion making and taking action [41]. In assessing, evaluating and choosing a particular pest control option, farmer's perception of the problem and of potential solutions is the most im‐ portant factor (Figure 2). Decision making in pest management, like other economic prob‐ lems in agriculture, involves allocating scarce resources to meet food demand of a growing population. In this process, agricultural producers have to make choices regarding the use of several inputs including labor, insecticides, herbicides, fungicides, and consulting expens‐ es related to the level and intensity of pest infestation and the timing of treatment. However, decision making process for pest control takes place in many levels at the fields. These vari‐ ous layers of decision making affect the whole strategy of pest control in a given cropping

system, region or country as well as the set of approaches and measures that are chosen to implement pest control programmes.

als over a range of environments. In practice, economic injury levels tend to be less rigorous‐ ly defined, but instead are nominal or empirical thresholds based on grower experience or generalized pest-crop response data from research trials. Although not truly comprehensive, such informal EILs in combination with regular monitoring efforts and knowledge of pest biology and life history provide valuable tools for planning and implementing an effective IPM programme. However, because growers will generally want to act before a population reaches EIL, IPM programmes use the economic threshold (Figure 3). The concept of eco‐ nomic threshold implies that if the pest population and the resulting damage are low enough, it does not pay to take control measures. In practice, the term economic threshold has been used to denote the pest population level at which economic loss begins to occur

Integrated Management of *Helicoverpa armigera* in Soybean Cropping Systems

http://dx.doi.org/10.5772/54522

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and indicate the pest population level at which pest control should be initiated [50].

**Figure 3.** Graph showing the relationship between the economic threshold (ET) and economic injury level (EIL). The

Economic injury level and economic threshold of *H. armigera* on some crops was estimated by several researchers (Table 2). In the case of *H. armigera* on soybean, these thresholds are poorly defined and a little information in this regard is available. However, economic thresholds; especially economic injury level; are dynamic and can be varied from year to year or even from field to field within a year depending on crop variety, market conditions, development stages of plant, available management options, crop value and management

arrows indicate when a pest control action is taken.

costs (Table 2).

**5.1. EIL and ET for** *H. armigera* **on different crops**

**Figure 2.** The process of decision making in IPM. (after Reichelderfer *et al*. [47]) 1. The way in which control options are assessed will depend on the farmer's objectives. Subsistence farmers may select for a guaranteed food supply, while commercial farmers are more concerned with profit. 2. The number of options that a farmer can feasibly use will depend on the constraints set by the resources available. 3. Compare the cost-effectiveness of alternative practices.
