Performance of sequential herbicides in dry-seeded rice in the Philippines

•Pre-emergence fb two post-emergence herbicides performed better than pre-emergence fb one post-emergence herbicide.•Pre-emergence herbicides must be used in DSR to achieve effective weed control and high grain yield.•Herbicides are the most effective and reliable weed management tools in DSR systems.•DSR systems needed the integration of agronomic practices with herbicides.

Economical and sustainable weed management in dry-seeded rice (DSR) depends on appropriate combinations of potential pre-emergence and post-emergence herbicides. A field study was conducted during the dry seasons of 2013 and 2014 at the International Rice Research Institute, Philippines, to evaluate the weed control efficiency of some pre- and post-emergence herbicide combinations in a DSR system. The herbicide treatments were: (i) oxadiazon 750 g ai ha−1 was sprayed at 1 DAS fb 2,4-D 500 g ai ha−1 at 28 DAS; (ii) oxadiazon 750 g ai ha−1 was sprayed at 1 DAS fb bispyribac-sodium 30 g ai ha−1 at 14 DAS fb 2,4-D 500 g ai ha−1 at 28 DAS; (iii) oxadiazon 750 g ai ha−1 was sprayed at 1 DAS fb bispyribac-sodium 45 g ai ha−1 at 14 DAS fb 2,4-D 500 g ai ha−1 at 28 DAS; (iv) bispyribac-sodium 30 g ai ha−1 was sprayed at 14 DAS fb 2,4-D 500 g ai ha−1 at 28 DAS; and (v) bispyribac-sodium 45 g ai ha−1 was sprayed at 14 DAS fb 2,4-D 500 g ai ha−1 at 28 DAS. The lowest weed density (22–28 plants m−2) and biomass (7–16 g m−2) were found in the plots treated with oxadiazon fb bispyribac-sodium 45 g ha−1 fb 2,4-D. However, weed density and biomass in this treatment were similar to that in the treatment oxadiazon fb bispyribac-sodium 30 g ha−1 fb 2,4-D. The highest weed density (123–239 plants m−2) and biomass (108–149 g m−2) were recorded in the plots treated with bispyribac-sodium 30 g ha−1 fb 2,4-D. The plots treated with oxadiazon fb bispyribac-sodium 30 g ha−1 fb 2,4-D had 12–14% higher rice grain yield than the plots that did not receive bispyribac-sodium (i.e., oxadiazon fb 2,4-D), and 20–25% higher grain yield than the plots that did not receive oxadiazon (i.e., bispyribac-sodium 45 g ha−1 fb 2,4-D). The results suggest that pre-emergence herbicides must be used in DSR to achieve effective weed control and high grain yield.