Weed Management Strategies in Direct wet-seeded Rice Culture under the ecological Conditions of D. L Khan, Pakistan. by KHIZAR HAY AT, INAYAT ULLAH AWAN AND GUL HASSAN Field experiments were conducted at Agricultural Research Institute Dera Ismail Khan, Pakistan during 1999 and 2000, to develop a viable and economically feasible weed management technology for the farmers of the area. The objective of this study was to establish an appropriate Weed management Strategy for effective control of weed flora in direct wet seeded rice. The experiments were conducted using split-plot arrangements in a Randomized Complete Block Design with a sub-plot size of 5m x 3m having three replications, during both years. The first experiment included IR-6, IR-9 and KS-282 varieties in main plots seeded on five different dates in sub-plots. The seeding was done from May 9 to June 18 at 10-day interval, during both the years. The results revealed that seeding of KS-282 on June 18 resulted in significantly lower weed population (m*2), low dry weed biomass (g m''2), greater number of spikelets per panicle, more 1000-grain weight (g), higher net income and Benefit Cost Ratio (BCR) values. However, June 18 seeding was at par with June 8 for number of panicles (m''2), number of days to maturity, paddy and straw yield (t ha*1). Besides, June 8 seeding had lower sterility percentage and greater number of tillers (m*2). The second trial consisted of three seeding rates of 60, 90 and 120 kg ha''1, in main plots, and oxadiazon (Rostar 12 L) @ 0.240 kg a.i, oxadiargyl (Topstar) 0.80 kg a.i, pretilachlor (Rifit) 0.50 kg a.i. and acetachlor (Acelor) 0.125 kg a.i. ha*1 in the sub-plots and were applied at post-emergence stage. Weedy check was also included in the trial. Both the pretilachlor and acetachlor application proved their efficacy against the grasses and sedges and improved yield parameters, increased net return and BCR values over other herbicides and weedy check, when 120 kg ha*1 seed rate was used. In the third experiment, four above mentioned herbicides including a weedy check plot were kept in sub-plots, while herbicides application intervals of 3, 6 and 9 weeks after seeding (WAS), were assigned to main plots. Pretilachlor application showed its superiority in terms of xixhigher paddy and straw yield (ha''1), number of panicles m''2, number of spikelets panicle''1, 1000-grain weight (g), lower dry weed biomass (g m''2) and sterility %, higher net income and BCR values when applied 3 WAS. While, averaging over the intervals of herbicides application, oxadiargyl was at par with pretilachlor for weed population (m''2), plant height (cm), tillers m''2, spikelets panicle''1, 1000-grain weight (g) and straw yield (t ha''1). However, these herbicides were statistically similar for paddy yield (t ha''1), harvest index, and number of panicles (m''2) during the second year of the trial. Oxadiargyl also resulted higher BCR values when applied 9 WAS. Oxadiargyl, pretilachlor and acetachlor controlled the sedges to the extent of 90.7 % and grasses to the tune of 86.3- 86.7 % when applied 3 WAS. In the fourth experiment, IR-6, IR-9 and KS-282 of the coarse group and Basmati-385, Basmati-370 and Basmati-198 from the fine group of rice varieties; assigned to the sub-plots were treated with acetachlor @0.125 kg a.i. and pretilachlor 0.50 kg a.i.ha''1, that were placed in main plots. Weedy check plot was also planted for comparison. Coarse and fine rice varieties responded well to herbicide application and had lower weed population (m''2) and dry weed biomass (g m''2) than weedy check. Acetachlor application to KS-282 gave numerically less dry weed biomass. Fine rice varieties produced significantly less dry weed biomass than coarse varieties but were at par with each other for both these parameters. Coarse variety KS-282 produced the maximum number of tillers and panicles (m''2), lower sterility %, more 1000-grain weight (g), paddy and straw yield (t ha''1) and harvest index, and were statistically at par with those recorded for IR-6. Variety IR-9 was the most early- maturing, while tallest plants were produced by Basmati-198; whereas the maximum spikelets per panicle were recoded for Basmati-370. Acetachlor application resulted in the highest net return and BCR values in Basmati-198 during the first year while, during the second year KS-282 gave higher BCR value. Pretilachlor when applied to Basmati-198 gave the highest net income and BCR during both the years. While, in the fifth experiment, Clamazone @ 0.247 kg a.i.ha''1, in addition to all the previously used four herbicides and the weedy check was tested in sub-plots. The main plots comprised hand weeding 6 and 9 WAS or no weeding. In the last experiment, pretilachlor, clamazone and acetachlor when followed one hand weeding each 6 and 9 WAS resulted in increased paddy and straw yield (t ha''1), harvest index, minimum weed population (m''2), dry weed biomass (g m''2), and lower sterility percentage than oxaziazon and oxadiargyl and the weedy check, though these three herbicides were statistically at par with each other for these parameters. However, numerically higher values for all the parameters were recorded for the pretilachlor xxapplication. The interaction of pretilachlor herbicide with hand weeding 6 WAS produced the maximum paddy yield. Higher BCR value was observed for acetachlor application with no hand weeding (herbicide alone), but pretilachlor gave higher BCR when supplemented with hand weeding 6 and 9 WAS. Pretilachlor application followed by one hand weeding at 6 WAS gave the excellent control of grasses and sedges. It is concluded from the research that direct seeding of course varieties of rice during the June at 120 kg 2nd ha''1 seed rate, pretilachlor application @ 0.240 kg a.i. ha''1 3 week of WAS and combined with hand weeding 6 WAS is the best strategy for higher grain yield of rice in the area.