Rice pest constraints in tropical Asia: Characterization of injury profiles in relation to production situations

A protocol for characterizing patterns of rice cropping practices and injur ies due to pathogens, insects, and weeds was developed and used in six site s in tropical Asia covering a wide range of environments where lowland rice is cultivated. The data collected in a total population of 456 individual farmers' fields were combined to site-specific weather data and analyzed us ing nonparametric multivariate techniques: cluster analyses with chi-square distance and correspondence analyses. The main results are: (i) patterns o f cropping practices that are common across sites can be identified; (ii) c onversely, injury profiles that are common across sites can be determined; (iii) patterns of cropping practices and injury profiles are strongly assoc iated at the regional scale; (iv) weather patterns are strongly associated with patterns of cropping practices and injury profiles; (v) patterns of cr opping practices and injury profiles allow for a good description of the va riation in actual yield; and (vi) patterns of cropping practices and injury profiles provide a framework that accurately reflects weather variation an d site diversity, and reliably accounts for variation in yield. The mean es timated yield across sites (4.12 t ha(-1)) corresponds to commonly cited av erages in the region and indicates the potential for increased productivity with better management practices, especially an improved water supply. Inj uries due to pests are secondary compared with other yield-limiting factors . Injury profiles were dominated by stem rot and sheath blight (IN1); bacte rial leaf blight, plant hoppers, and leaf folder (IN2); and sheath rot, bro wn spot, leaf blast, and neck blast (IN3). IN1 was associated with high (mi neral) fertilizer inputs, long fallow periods, low pesticide use, and good water management in (mostly) transplanted rice crops of a rice-rice rotatio n. IN2 was associated with direct-seeded rice crops in an intensive rice-ri ce rotation, where fertilizer and pesticide inputs are low and water manage ment is poor, or where fertilizer and pesticide inputs are high and water m anagement is adequate. IN3 corresponds to low input, labor intensive Gland weeding and transplanting) rice crops in a diverse rotation system with unc ertain water supply. Weed infestation was an omnipresent constraint. This s tudy shows the potential for developing pest management strategies that can be adapted throughout the region, rather than being site-specific.