Evaluation of herbicide mixtures for weed management in direct seeded aerobic rice

Abstract:

Can herbicide mixtures offer a dependable answer to the growing weed menace in direct seeded aerobic rice? This question has become pressing as aerobic rice cultivation expands across water-scarce regions, and weeds remain the single largest biological constraint to grain yield. The present research was carried out during the wet season of 2023 at the research farm of Visayas State University, Baybay, Leyte, to evaluate five herbicide mixture treatments against a weedy check and a season-long weed-free control in a randomised complete block design with three replications. Treatments included pre-emergence pendimethalin (1000 g a.i. ha⁻¹) followed by post-emergence bispyribac-sodium (25 g a.i. ha⁻¹), pendimethalin followed by fenoxaprop-p-ethyl (60 g a.i. ha⁻¹), oxyfluorfen (200 g a.i. ha⁻¹) followed by bispyribac-sodium, and pendimethalin alone, compared against the controls. Observations on weed density, weed dry weight, weed control efficiency, crop growth parameters, and grain yield were recorded at 30, 60, and 90 days after sowing. Pendimethalin followed by bispyribac-sodium recorded the lowest weed density (24.6 no. m⁻²) and the highest weed control efficiency (71.8%) at 60 DAS, which translated into the highest grain yield (4.38 t ha⁻¹), statistically at par with the weed-free check. The weedy check suffered a yield penalty of 46.6% relative to the best treatment. These results point to the sequential application of pendimethalin and bispyribac-sodium as a practical, cost-effective weed management option for aerobic rice under direct seeding in the Visayas region.