Determinants of parasitic weed infestation in rainfed lowland rice in Benin

The parasitic weed Rhamphicarpa fistulosa is threatening rainfed lowland rice production in Benin. The aim of this study was to explore factors (such as biophysical characters of the rice growing environment, farmers' management practices, and socioeconomic characteristics) that affect the infestation of rainfed lowland rice fields by R. fistulosa and farmers' ability to cope with the problem. Data were collected from 231 rice plots located in 12 inland valleys infested by Rhamphicarpa in Benin. Data were analyzed using a double hurdle model, which analyses both the likelihood (of occurrence) and the severity of infestation. Results showed that 72% of the surveyed rice plots were infested by R. fistulosa and the average severity was 109 plants m−2. The likelihood of infestation was higher on poorly fertile soils and fields located in the inland-valley bottom, and it decreases through timely use of herbicides and ploughing. Severity of infestation was higher on rice plots cultivated by female-headed households farmers and reduced through management practices such as late sowing, timely application of post-emergence herbicide, three hoe or hand weeding operations, medium-rate fertilizer application and prolonged fallow. Likelihood and severity of infestation were found to be negatively correlated. These findings suggest that farmers can reduce the likelihood and the severity of infestation of their plot as long as they are aware of factors causing the problem given their access to and management capacity of production resources.