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Figure 2.2 Linear and threshold damage relationship
Source: Norton 1993
The damage relationship describes the level of loss associated with different levels of pest attack. Although this relationship is often non linear, for
decision making purposes it is only necessary to distinguish two forms of damage relationship. A linear damage relationship Figure 2.2a is associated with pest
that are vectors of disease, where the crop is unable to compensate, or where the major concern is the presence of during a pest causing quarantine or cosmetic
damage. In this case, the slope of the damage relationship is the critical factor determining the degree of control required.
The second relationship, threshold damage, has the form shown in Figure 2.2b. there is a level of tolerance associated with low levels of pest attack, or
compensation to damage occurs, particularly where this damage is to part as of the plant which are not part of the marketable yield, such as leaves and roots of fruit
crop. 2.3.6 Technique of Integrated Pest Management IPM
In terms of IPM methods, IRRI 2009, point out that components of IPM practices include:
1. Pest-resistant crop varieties
: this is the easiest, effective, compatible, economical and practical method among all the pest management practices.
Such crop varieties are extensively used in pest prone areas as a principal method of IPM or as a supplement to other pest management strategies.
Yield
Pest Density a
Yield
Pest Density T
b
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2. Cultural methods : these refer to good agronomic practices that enhance the
crop productivity and also suppress the pest population. The cultural practices which are commonly used for rice system are;
a. Proper sanitation: timely removal of weed to reduce the pest survival and reduce the chance or any carryover of the pest
b. Proper water management timely irrigation and good drainage system is
required to control plant hoppers. c.
Proper spacing: provision of alley ways of 30 cm. Width after 2-3 m bed planting particularly in the white backed plat hopper and brown plant
hopper prone area, proves helpful d.
Time planting: timely and synchronous planting can reduce the occurrence of insect pests like yellow stem borer.
e. Balanced fertilizer: judicious and optimum dose of nitrogen and other
fertilizer based on soil testing is essential. Split dosage of nitrogen can also reduce the risk of gall midge, leaf hopper, brown plant hopper, etc.
3. Biological control
: biological control is the mainstay of the IPM strategy. Out of 100 phytophagus insects having potential of becoming pests, only a
few attain the pest status while the rest are kept under check by their natural enemies. Even those which attain the pest status have biological agents like
predators, parasites ,and pathogens which decrease their population in the rice ecosystem, it is very important to conserve the natural enemies of pest in the
field. Avoid the use of broad spectrum pesticides when natural enemies are abundant.
4. Chemical control : application of pesticides is no doubt one of the quickest
