Red rice (Oryza sativa L.) and barnyardgrass (Echinochloa spp.) biotype susceptibility to postemergence‐applied imazamox

Abstract

Pot experiments were conducted to evaluate the level of imazamox tolerance in five red rice (Oryza sativa L.) and four barnyardgrass (three Echinochloa crus‐galli (L.) Beauv. and one Echinochloa oryzoides (Ard.) Fritch) morphologically distinct biotypes collected from rice fields in northern Greece. The susceptibility of barnyardgrass biotypes to propanil was also studied. Red rice biotypes were not controlled by imazamox applied at 40 g ha−1. In contrast, 80 g imazamox ha−1 provided 56–84% red rice control (averaged across shoot number and fresh weight reduction). Not all barnyardgrass biotypes were susceptible to imazamox applied postemergence. However, propanil applied at 2.6 kg ha−1 controlled the E. crus‐galli biotypes well, but propanil applied at rates of 2.6 and 5.2 kg ha−1 was not effective in reducing the shoot number and fresh weight of the E. oryzoides biotype. Propanil applied at 10.4 kg ha−1 reduced the shoot number and fresh weight of this biotype by 78 and 85%, respectively. In most cases, a linear equation (y = % of control, x = g ha−1) provided the best fit for regressions between red rice or barnyardgrass shoot number or fresh weight and imazamox rates. The results of this study suggest that postemergence application of imazamox is not effective against all red rice and barnyardgrass biotypes found in the rice fields of Greece and that significant variability regarding herbicide efficacy among biotypes might exist.