Abstract/Summary

Lowland rice farmers in Nigeria handweed and uniformly apply herbicides across whole fields. This study aimed to adapt these traditional practices to explore whether farmers could target interventions more precisely to weed patches. Questionnaires were administered to 281 respondents and farmer’s claims were verified by field sampling and trials in controlled environments. The farmers were typically losing 55-91% of their rice yield to weeds. Moreover, 71% reported spatially variable weed distribution in their fields with 69% attributing this to variations in flooding depth. Intensive sampling of two fields confirmed farmers’ claims. For example, Nymphaea maculata Schumach. & Thonn accumulated at flooding depths >6cm while Echinochloa spp. mainly occurred in “drier” parts with <3cm flooding. The farmers’ knowledge of the weed distribution in their fields was, on average, 81% accurate compared to an intensive assessment. The farmers claimed that weeds were glyphosate resistant, but this was found to be incorrect when recommended doses (RD) were applied in controlled-environment studies for Chrysopogon nigritanus (Benth.) Veldkamp and Panicum laxum Sw (Steinchisma laxum (Sw.) Zuloaga). These species did, however, tolerate 1 /4 and 1 /8 rate glyphosate applications respectively, while 1 /8 th rate had an hormetic effect on tiller production of both weeds. Flooding did not influence the glyphosate susceptibility of the rice cultivars but reduced the dose for 50% efficacy (ED50) of P. laxum by 58%. The claims that rice tolerated glyphosate could not be validated, the ED50 of the rice plants being as low as 2- 4% of the RD. The study achieved its aim of raising awareness of precision agriculture without use of technology and when carrying out participatory budgets, the farmers anticipated a 37% reduction in weeding costs. Consequently, 85% and 63% of participating respondents indicating their willingness to adopt site-specific handweeding and herbicide application, respectively; some adopted these options immediately after the study.