Abstract
This experiment were performed as a part of the fundamental works for the purpose of setting a weeding system in field management. It was planned to use nine different weeding treatment at different growth stage of upland rice crop and the influence of weed volumes at the various .growth stage on the growth and yield of the crop was observed. Upland riceplant were very sensitive to weeds, especially to those grow very rapidly, such as Chenopodium album, Polygonum oriental and Amaranthus Blitum, for a few weeks after germination. Digitaria ciliaris grew more in the field, but they were not injurious in this period. When weeds are removed two or three weeks after germination, upland rice plants were not injured by weeds for a few weeks after this weeding even if weeds grow again. The next period when crops were more injured by weeds, was after the stage of flower bud differentiation. So, by weeding only twice at these two periods the growth and the yield of upland rice would be free from the influence of weeds.
