Dynamics Of Weed Flora In Speargrass (Imperata Cylindrica (L.) Raeuschel) Dominated Fallow As Influenced By Chemical Weed Control And Row Spacing In Soybean (Glycine Max (L.) Merr).

Two Field trials were conducted at Ijorimenger and Asukunya in Tarka Local Government Area of Benue State (07o 14 N, 08o 37 E), in 2007 and 2008 cropping seasons, with the objective to determine the influence of chemical herbicides and row spacing on the control of speargrass and population dynamics of weed flora. Pretillage glyphosate at the rate of 2.16 kg a.i/ha followed by hoe weeding at 6 WAP and fluazifop-p-butyl at the rate of 0.25 kg a.i/ha followed by hoe weeding at 6 WAP significantly reduced speargrass density compared with hoe weeding control at 3 and 6 WAP. A total of 22 and 16 weed species were found under fallow and in the soil. The weed flora at preharvest of soybean, was dominated by Ageratum conyzoides (L.) and Rottboellia cochinchinensis (Lour ), which thrived in plots treated with postemergence fluazifop-p-butyl at the rate of 0.25 kg a.i/ha and pretillage glyphosate at the rate of 2.16 kg a.i/ha respectively. The preponderance of weeds not found under fallow but which emerged after disturbance indicated that there was a change in weed flora composition and density. These results suggest that the use of pretillage glyphosate and fluazifop-p-butyl at 2.16 and 0.25 kg a.i/ha respectively followed by hoe weeding at 6 WAP was effective in suppressing speargrass seedling emergence and change in weed flora composition.