Chemical control of weedy rice in precise hill-direct-seeded rice in South China

Precise hill-direct-seeded rice, which is both cost- and labor-saving, is based on the direct seeding of rice by using a precision rice hill-drop drilling machine. Weedy rice (Oryza sativa f. spontanea), also known as red rice, is a major weed in precise hill-direct-seeded rice, causing an 80% yield loss and a reduction in grain quality. The aim of this study was to evaluate the control efficiency of weedy rice by pretilachlor (a pre-emergence herbicide) and fenclorim (a safener) and their safety for precise hill-direct-seeded rice in two consecutive years. The amount of rice seed germination was accelerated by soaking the seeds in the safener at 0.67gaiL1 for 1h before sowing. The pre-emergence pretilachlor treatments were applied 2 days after sowing cultured rice. The inhibition of the shoot fresh weight of the cultured rice was reduced by 3.3, 6.4 and 7.4% with 450, 900 and 1350gaiha1 of pretilachlor at 32 days after sowing (DAS) and that of the root fresh weight was reduced by 2.6, 4.9 and 8.1%, respectively. With fenclorim and pretilachlor in a precise hill-direct-seeded rice field in 2010 and 2011, the weedy rice control efficiency at 32DAS was reduced by 100 and 98.0%, respectively. The pre-emergence pretilachlor treatments that were applied at 2DAS were much more efficient in the weedy rice control and less inhibitory to the cultured rice growth. The rice yield was increased by 26.126.7% in the mechanical precise hill-direct-seeded rice, relative to the manual-seeding rice, with the application of fenclorim and pretilachlor.