Weed Growth and Grain Yield, as Affected by Herbicides, in Dry-seeded Rice in Sri Lanka

Dry-seeded rice (Oryza sativa L.) is an emerging establishment system in irrigated areas in many Asian countries, including Sri Lanka. A field experiment was conducted in the major (Maha) 2011/12 and minor (Yala) 2012 seasons at the research farm of the Rice Research and Development Institute, Sri Lanka, to evaluate the efficacy of several herbicides in an irrigated dry-seeded rice system. Herbicide treatments included propanil, followed by MCPA (2-methyl-4-chlorophenoxyacetic acid), pendimethalin, oxadiazon plus propanil, oxyfluorfen, and pendimethalin, followed by fenoxaprop plus ethoxysulfuron, oxadiazon plus propanil, followed by fenoxaprop plus ethoxysulfuron, and oxyfluorfen followed by fenoxaprop plus ethoxysulfuron. The efficacy of herbicides varied across years. All herbicide-treated plots had lower weed density and weed biomass than the untreated plots. The results suggested that oxyfluorfen applied alone provided the poorest weed control. Generally, there was no effect of the additional spray of fenoxaprop plus ethoxysulfuron on weed biomass at 42 days after planting. However, grain yield was higher in the plots sprayed with the pre-emergence, followed by post-emergence herbicides, compared with the plots sprayed with only pre-emergence herbicide(s). The results suggest that different herbicide options are available in Sri Lanka to effectively control weeds in dry-seeded rice systems.