Red rice (Oryza sativa L.) is considered the worst weed to the rice crop in the State of Rio Grande do Sul, Brazil. The difficulty of its chemical control and the high degree of infestation in rice fields determine the necessity of developing systems for cultural control. The objective of this study was to evaluate the effects of three sowing rates, three row spacings and two irrigated rice cultivars on red rice control, grain yield and agronomic characteristics of irrigated rice under minimum tillage system. The experiment was conducted in 1994/95, at Rice Experimental Station, IRGA, Cachoeirinha/RS. The treatments consisted of row spacings of 13.5, 20 and 30 cm, sowing rates of 75, 150, and 225 kg/ha and cultivars BR-IRGA 410 and IRGA 416. The results indicated that increasing of sowing rate associated with narrowing row spacing in the taller cultivar and higher season, BR-IRGA 410, gave higher competitivity to rice with regard to red rice. The use of early season rice cultivar, IRGA 416, reduced the amount of red rice seed that fallen to the ground.
Cultural control; sowing rates; row; weed; oryza sativa