The increasing use of synthetic chemicals for pest control in rice has
become an overwhelming economical border, and more important, it could pose
a serious threat of the environment. In addition, the extensive use of
synthetic herbicides has been the cause for the evolution of
herbicide-resistant barnyardgrass worldwide. This weed species is the most
competitive weed in rice after the red rice. Thus, this study was conducted
to examine the combination effects of aqueous sunflower leaf extracts with
lower rate of pretilachlor on barnyardgrass emergence and growth in Marang
(sandy loam) and Seberang (silt loamy) soil series under glasshouse
conditions. Interestingly, the ED95 values (rate that causes 95%
inhibition) of pretilachlor for emergence and shoot fresh weight
(SFW) of barnyardgrass were reduced by 79 and 82%,
respectively, when being mixed with sunflower leaf extracts in Marang
series. In contrast, the addition of sunflower leaf extracts increased
ED95 value of pretilachlor in Seberang series. Rice seedlings
at 4 and 8 d after sowing (DAS) were found to be tolerant to this mixture
treatment. However, root growth of rice seedlings were inhibited at 0 and 2
DAS. These results suggest that sunflower leaf extracts have potential to
reduce rate of pretilachlor for inhibiting emergence and growth of
barnyardgrass without injuring rice seedlings in rice fields depending on
soil types and growth stage of rice.