Effect of herbicide and moisture level onRottboellia cochinchinensisandCyperus rotundusin upland rice

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Abstract
Field experiments were conducted to determine the effectiveness of herbicides in controlling Rottboellia cochinchinensis (Lour.) W. D. Clayton and Cyperus rotundus L. in upland rice (Oryza sativa L.) at different moisture regimes as imposed by a line source sprinkler system. Preemergence application of pendimethalin [N‐(1‐ethylpropyl)‐3,4‐dimethyl‐2,6‐dinitrobenzenamine] was highly effective in controlling R. cochinchinensis irrespective of soil moisture after herbicide application. Bentazon [3‐(1‐methylethyl)‐(1H)‐2,1,3‐benzothiadiazin‐4(3H)‐one 2,2‐dioxide] and 2,4‐D [(2,4‐dichlorophenoxy)acetic acid] applied at postemergence effectively controlled C. rotundus when moisture supply was well above pan evaporation. These herbicides also had no adverse effect on rice stand and resulted in higher yield over the control. Water application rates above upland pan evaporation for a season‐long period was essential to obtain a high response to weed control either by herbicides or hand weeding. The data suggest that proper weed control by herbicides or hand weeding will not result in high upland rice grain yields if moisture level from rains fall below the critical level.