Influence of Repeated Application of Herbicides on Weed Succession and Yield of Rice Based Cropping System in India

Field experiments were conducted to determine the effect of continuous application of herbicide on weed growth and yield of rice-rice-pulse cropping sequence over nine cropping seasons. The dominant weed species were Marselia quadrifolia, Echinochloa crus-galli, Cyperus difformis and Monochoria vaginalis. In hand weeded plots M. quadrifolia and the annual grass E. crus-galli were dominant in the early crops; E. crus-galli dominated in the later crops, with a shift to M. vaginalis in dicots. Annual application of herbicides caused a population shift from dicots to monocots, particularly grasses. Among grasses, Leptochloa chinensis , a difficult weed to control replaced dicots and reduced E. crus-galli. Combined chemical treatment and manual weeding as well as manual weeding controlled the weed growth and maintained the yield of rice throughout the period of study.