Chemical control of weedy rice in pre-germinated wet seeded rice in Thailand

摘要

Weedy rice (Oryza sativa f. spontanea) is a noxious weed in direct seeded rice (Oryza sativa L.) in the Central Plain of Thailand. By 2006, the area of invasion of this weed had expanded to 200,000 ha. Farmers use several methods to control weedy rice; however, chemical control is needed. A field experiment was conducted in the wet season 2005 in Supanburi Province where weedy rice infestation was >70%. Rice herbicides with different modes of action were used. Moderate phytotoxicity to rice plants was observed after application of oxardiargyl and dimeth-anamid; however, rice plants recovered within two weeks. In the untreated check, weedy rice density was 264 panicles m~(-2), which caused rice yield losses of up to 2.5 t ha~(-1) when compared with oxadiargyl at 0.25 kg a.i. ha~(-1) applied at nine days after sowing (DAS). Two applications of herbicide gave excellent control of weedy rice resulting in higher rice yields than a single application. The best combination of herbicides were flufenacet at0.113 kg a.i. ha~(-1) or dimethanamid at 0.28 kg a.i. ha~(-1) applied at two days before sowing rice and followed with oxadiargyl at 0.25 kg a.i. ha~(-1) at nine DAS or a tank mixture of profoxydim + quinclorac at 0.02 + 0.09 kg a.i. ha~(-1) at 7 DAS. With those combinations, the infestation of weedy rice was reduced by >90% and rice yield was substantially increased by up to 3.9 t ha~(-1). Although herbicides are effective for controlling weedy rice, other control methods such as using clean seed, weed eradication prior to planting, hand pulling and weedy rice panicle removal are also recommended to prevent the evolution of resistance to herbicides in the weedy rice populations.