Effect of weed control period on weed dominant species and growth of SPT1 rice variety under transplanted cultivation

Abstract

     Weeds are one of the major causes of yield losses in rice production. The understanding of weed species and their specific occurrence can improve an effective timing for weed control which is an important component of integrated weed management. The objectives of this study were to determine effect of different weed control timing on weed species and weed dominant species and to evaluate effect of weed control timing on growth and yield component of rice. The experiment was laid out in RCBD with four replications. Seedlings of SPT1 rice variety were transplanted in the paddy field that was arranged into four treatments; T1 weed-free, T2 weed control before maximum tillering stage (MT), T3 weed control after MT and T4 weedy. At the ripening stage of rice, weed species, weed density, weed dry weight and summed dominance ratio (SDR) were recorded and then growth and yield component of rice were estimated. The results showed that T2 had the most weed species consisted of swamp morning-glory (Ipomoea aquatica Forsk.), yellow bur-head (Limnocharis flava Buch.), water primrose (Ludwigia adscendens (L.) Hara.) and torpedo grass (Panicum repens Linn.), while T3 and T4 was covered by swamp morning-glory and T4 was highest weed density. Weed dominant species in transplanted rice cultivation were swamp morning-glory and yellow bur-head which they were aquatic weeds and highly tolerance to submergence. Every treatments of weed-rice competition decreased growth and yield of rice comparing to T1, especially in T4. The competition of weed and rice at before (T3) or after (T2) MT stage had no difference on plant height, number of filled grain, number of unfilled grain and 1000-grain weight. However, T3 showed more severe decreasing of tiller numbers and grain yield than T2, suggesting that the sensitive growth stage of rice to weed competition was vegetative stage.