Speargrass invasiveness in Derived Savanna (DS) and southern Guinea Savanna – northern fringe (SGS) is influenced by the rainfall amount and cultural practices (weed management methods, tillage method and plant spacing). Studies were conducted between 2015 and 2016 in Eruwa (DS) and Kishi (SGS), to investigate the problem of weed incidence in farmers’ fields and the influence of weed control methods adopted on invasiveness with structured questionnaire; the invasiveness of predominant weed [speargrass – Imperata cylindrica (L.) Reauschel]. The geographical analysis were carried out in an ArcGIS environment. Results showed that speargrass was the predominant weed identified by 100% and 90% of farmers in DS and SGS respectively. Other weeds identified were broadleaf (54%), grass (38%) and sedge (8%) in both locations. Manual weeding (slashing and hoe-weeding) was the most common weed control method used among respondent farmers in the two agro-ecologies. 60% and 50% of the farmers adopted manual weeding in DS and SGS respectively. This was followed by chemical weed control (DS 30% and SGS 40%) and manual + chemical was practiced by 10% each of farmers in both agro-ecologies. Frequently used weed control methods followed the order of Manual weeding (MW) > Chemical weeding (CW) > Manual + chemical weeding (MW + CW). Average speargrass density in DS was 140 stands/sq.m (0 – 288 stands/sq.m), while the mean was 39 stands/sq.m (0 – 160 stands/sq.m) in SGS. Speargrass covered 288.07 sq.km (79.80% of surveyed area) with <50 stands/m2 in SGS, while 231.74 sq.km (57.60% of surveyed area) with density of 150 stands/sq.m in DS. Weed management methods and locations might have influenced speargrass invasiveness.
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