Characterization of rice pest constraints in Asia: an empirical approach

Abstract

A methodology has been developed which allows the risk posed by pests to be addressed in the context of shifting intensification levels of rice production in Asia. The term ‘pest’ is used here to encompass any harmful agent, including pathogens, insects, and weeds. This methodology combines two separate approaches: assessing risk probability, and quantifying risk magnitude. Risk probability may be defined as the probability of a particular pest combination occurring in a given production situation. It can be derived from surveys in selected sites. Yield loss — the gap between attainable and actual yields — is taken as one measure of risk magnitude. It is assessed from a crop loss data base developed from a series of field experiments, where inputs to the rice crop and pests are manipulated independently. The analysis indicates that rice tungro virus disease, rice sheath blight, and weed infestation correspond to very high risk magnitudes. Yield losses due to pest injuries are often strongly influenced by changes in production situation, and, therefore, by variation in attainable yield. The pattern of this relationship strongly depends on the nature of the pest, however. Different pest scenarios from contrasting production situations in Uttar Pradesh, Central Luzon, eastern Thailand and the Mekong Delta can be used to illustrate the present situation, and forward hypotheses on the future need of research at the system level.