Evaluation of preemergence herbicides for weed control in wet-seeded rice

摘要

Economic factors, such as the rising labor cost for transplanting and recent changes in rice production technology by intensification through double or triple cropping, have improved the desirability of direct seeding of rice under puddled conditions, although transplanting is still a major traditional method of crop establishment under lowland conditions (Pandey and Velasco 1999). Direct sowing of pregerminated seeds after puddling in lowlands is termed "wet seeding." Competition from weeds is a maj or constraint to the productivity of wet-seeded rice because rice has no growth advantage over weeds, as in transplanted rice. Grass weeds are also more difficult to hand weed at the transplanting stage because of their similar morphology to that of rice . Weeds have been reported to reduce the yield of wet-seeded rice by 15-70%. Direct-seeded rice covers 26% and 28% of the total rice area in South Asia and India, respectively (Pandey and Velasco 1999). It may become more popular if an effective weed con trol system is developed. The nonavailability of labor at the critical period of crop-weed competition and increased labor costs present problems at weeding in wet-seeded rice, At present, although many herbicides are available for transplanted rice, the ir effectiveness in wet-seeded rice has not been evaluated as a replacement for the traditional hand weeding, with its high labor requirement. This study was thus conducted to evaluate the performance of different preemergence herbicides for effective we ed control in wet-seeded rice in places where labor is scanty and costly.