Among the three weed groups, the grass density was affected by
weed control treatments more in DS14 but not so much in DS13
(Table 2). The lowest grass weed density was found in the plots
treated with oxadiazon fb bispyribac-sodium fb
fenoxaprop þ ethoxysulfuron (0 and 18 plants m2 in DS13 and
DS14, respectively), which was 66e100% lower than the weed
density in the oxadiazon only-treated plots. The plots that received
oxadiazon fb bispyribac-sodium and oxadiazon fb
fenoxaprop þ ethoxysulfuron had similar grass weed density to the
plots that received oxadiazon fb bispyribac-sodium fb
fenoxaprop þ ethoxysulfuron. Meanwhile, the six weed control
treatments affected broadleaved weed density in both years, with
the lowest density (4.2 and 140.6 plants m2 in DS13 and DS14,
respectively) found in the plots treated with oxadiazon fb
bispyribac-sodium fb fenoxaprop þ ethoxysulfuron. The application
of oxadiazon fb fenoxaprop þ ethoxysulfuron (fb 2,4-D fb MW)
reduced sedge density by 63% in DS14. Oxadiazon is used as a PRE
herbicide to control a broad spectrum of weeds in DSR systems;
however, its application should be followed by a POST herbicide
and hand weeding as reported in a previous study (Chauhan and
Abugho, 2013). In our study, we found that in the plots that were
given a single application of oxadiazon, weed density was 32e52%
higher than in the plots treated with oxadiazon fb bispyribacsodium
fb fenoxaprop þ ethoxysulfuron, which indicates that the
application of only PRE herbicides is not enough to provide sufficient
weed control in DSR systems. These results are also supported
by a previous study in which the application of oxadiazon alone
provided 60e75% weed control compared with a weed-free treatment
(Ishaya et al., 2007).