Efficacy and economics of different herbicides, their weed species selectivity, and the productivity of mechanized dry-seeded rice

• Highest net benefit can be achieved by using a PRE or early-POST herbicides.
• Use of POST herbicide according to the weed species present in the field is important.
• Selection of right herbicides is a cost-effective method for weed control in dry-seeded rice.

A field study was conducted in 2012 and 2013 at the International Rice Research Institute (IRRI) farm in Los Baños, Philippines, to evaluate the economic performance of PRE oxadiazon and pendimethalin, early POST butachlor plus propanil and thiobencarb plus 2,4-D, and late POST herbicides bispyribac-sodium and fenoxaprop plus ethoxysulfuron applied solely or sequentially. All herbicide treatments with PRE or early POST herbicides reduced total weed density by 85–100% and biomass by 80–100%, whereas late POST treatments reduced weed density by 32–50% and biomass by 40–62% compared with the nontreated weedy check. The highest grain yield was achieved in weed-free plots (5.9–6.1 t ha−1) and the lowest in weedy plots (0.2 t ha−1). Among the herbicide treatments, rice treated with oxadiazon, thiobencarb plus 2,4-D, and butachlor plus propanil followed by the late POST herbicides had grain yield increments of 23–25, 20 to 26, and 18 to 23 times that of the yield in weedy plots, respectively. The economic analysis showed that the sole application of oxadiazon provided the highest net profit and benefit-cost ratio in both years, which was similar to the treatments involving oxadiazon or early POST herbicides, followed by the sequential application of late POST herbicides.