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.
Nomenclature: Pretilachlor, 2-chloro-N-(2,6-diethylphenyl)-N-(2-propoxyethyl)acetamide; barnyardgrass, Echinochloa crus-galli (L.) Beauv., ECHCG; rice and red rice biotype, Oryza sativa L.; sunflower, Helianthus annuus L.
