Allelopathic effects of sunflower leaf extract and selected pre-emergence herbicides on barnyardgrass

Barnyardgrass has been the most frequently reported troublesome weed in rice fields because it is an aggressive invader that is difficult to control and reduces rice yields significantly. A laboratory study was conducted to determine the effects of sunflower leaf extract and pre-emergence herbicides, pretilachlor and thiobencarb, on shoot emergence and seedling growth of barnyardgrass. The sunflower leaf extract and the pre-emergence herbicides exhibited phytotoxic effects on barnyardgrass at different degrees of potency. It was found that sunflower leaf extract and thiobencarb are root inhibitors and strong shoot inhibitors respectively. Whereas, pretilachlor is a strong root and shoot inhibitor. The emergence and seedling growth of barnyardgrass were inhibited by 80 – 100% with increasing concentration of sunflower leaf extract from 10 – 15% (w/v). Comparatively, rice seedlings were more tolerant to sunflower leaf extract where rice emergence and growth were inhibited by 10 – 65% at the same concentrations. The present findings suggest the possibility of using sunflower leaf extract as a pre-emergence bio-herbicide for inhibiting seedling growth of barnyardgrass without injuring the rice seedlings. Keywords: allelopathy; pre-emergence bio-herbicide; Echinochloa crus-galli; rice; phytotoxicity