Effect of rice establishment methods on weedy rice (Oryza sativa L.) infestation and grain yield of cultivated rice (O. sativa L.) in Sri Lanka

Weedy rice is a great threat to rice production in Sri Lanka. Selective herbicides to manage weedy rice in conventional rice cultivars are not available in Sri Lanka. In the absence of appropriate chemical control measures, cultural approaches may help to achieve effective control of weedy rice. A study was conducted in two consecutive seasons in farmers€™ fields at three sites (Atalla, Samanthurai, and Girithale villages) in Sri Lanka to evaluate the effect of different establishment methods (farmers€™ practice, random broadcast, row seeding, seedling broadcast, and transplanted rice) on weedy rice infestation and rice yield. The farmers’ practice had a higher number of weedy rice panicles (60-80 m-2) than the random broadcast (39-48 panicles m-2), seedling broadcast (3-15 panicles m-2), and transplanted rice (1.3-3.0 panicles m-2) methods. The use of clean rice seeds in the random broadcast method reduced weedy rice seed production by 29-41% compared with the farmers’ practice (0.6-2.0 t•ha-1). Compared with the farmers’ practice, the seedling broadcast method reduced weedy rice seed production by 71-87% and transplanted rice by 95-98%; and increased rice yield by 27-49% (7.5-9.1 t/ha). At all three sites, the farmers€™ practice resulted in the lowest grain yield (5.1-6 .7 t/ha). Compared with the farmers€™ practice, the random broadcast and row seeding methods increased rice yield by up to 21% and 31%, respectively. The findings suggest that the use of clean rice seeds, the use of a row-seeded crop, and the adoption of different rice planting methods may help to suppress the spread of weedy rice.