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.