Selectivity and weed control efficacy of some herbicides applied to sprinkler irrigated rice (Oryza sativa L.)

Abstract

Sprinkler irrigation can reduce the irrigation water needed to grow rice. However, most available information on weed control with herbicides is related to flood irrigated rice because this is the main growing method. Field experiments were conducted at Zaragoza (Spain) during two years to study weed control and tolerance of sprinkler irrigated rice to several herbicides. The main weeds were Atriplex prostrata Bouchér ex DC., Cyperus rotundus L., Echinochloa crus-galli (L.) Beauv. and Sonchus oleraceus L. Rice cv Guadiamar was tolerant to preemergence (PRE) application of clomazone at 0.36 kg ha-1 and oxadiazon at 0.5 kg ha–1. PRE application of pendimethalin at 1.32 kg ha–1 combined with clomazone at 0.36 kg ha-1 decreased rice yield. Postemergence (POST) application of bentazon at 1.6 kg ha–1 + MCPA at 0.25 kg ha–1 did not injure rice but POST application of azimsulfuron at 0.025 kg ha–1 produced visual crop injury. Only treatments that controlled grassy weeds since rice was planted and by more than 80% at harvest time lead to acceptable rice yield (> 5,000 kg ha–1). Clomazone applied PRE at 0.36 kg ha–1 provided good control of grassy weeds (> 80%) and the highest rice yield, so it is recommended as a selective and efficacious PRE treatment for weed control of annual weeds in sprinkler irrigated rice. The perennial purple nutsedge was difficult to control at high plant densities (> 150 plants m–2) and the recommended herbicide is azimsulfuron applied at POST at 0.02 kg ha–1.