A characterisation of rice pests and quantification of yield losses in the rice-wheat system of India

The relationship between rice cropping practices, biotic constraints, and rice yield levels in the eastern part of Uttar Pradesh, India was studied. The investigation was conducted at the centre of a geographic area representative of the rice-wheat system of South Asia, and covers a large diversity of production situations undergoing intensification. A survey procedure was used to collect data for 3 consecutive years (1993-1995) in 251 individual farmers' fields. Two analytical approaches were used, the emphasis shifting from yield determining variables, that are mostly qualitative in nature, to quantitative, and predominantly yield-reducing, variables. The first approach was intended to characterize relationships among variables using cluster and correspondence analyses, while the second approach was aimed at generating yield loss estimates using combinations of principal components and step-wise multiple regressions. Seven patterns of cropping practices were distinguished, reflecting a wide variation in production situations, especially in terms of use of fertilizers and manure, and degree of water control. Six types of disease profiles, four insect injury profiles, and four weed infestation patterns were identified. Correspondence analysis, based on patterns of cropping practices and injury profiles, yielded a path of increasing attainable yield associated with varying levels of intensification and combinations of injuries. The use of principal component analysis with multiple regression generated estimates of yield reductions due to rice diseases, insects and weeds. The analysis highlighted the effects of changes in patterns of cropping practices on injuries caused by weeds, brown spot, sheath blight and dead hearts. The significance of these findings with respect to current and future IPM needs is discussed. (C) 1997 Elsevier Science Ltd.