Speargrass [Imperata cylindrica (L.) Raeuschel] Growth in Relation to Season, Rainfall and Temperature Patterns of Southern Agro-ecologies of Nigeria

Speargrass posed a major constraint to crop producion in some agroecologies in Nigeria.  Hence, the study was conducted to investigate the influence of seasons, rainfall and temperature patterns on speargrass components growth with the view to improve its management. This study was conducted between 2014 and 2016 at Eruwa (7˚32’0˚N, 3˚ 25’0 ˚E, 187m altitude) in Derived savanna (DS) and Kishi (08˚.98’N, 003˚.94’E; 364m altitude) in the southern Guinea savanna (SGS)–northern fringe agroecologies of Nigeria. Twelve months of the year starting from July were randomly assigned to plots in an abandoned speargrass infested farmland, replicated three times and arranged in Randomized Complete Block Design. Monthly temperature, rainfall and speargrass samples (shoot and rhizome) were measured. Results showed that rainfall amount varied across the months in both locations. The highest rainfall was recorded in September (264.20 mm) and hottest month was May, 2016 (28.5oC) in Derived savanna between 2014 and 2016 (Table 1). Kishi had 186 mm rainfall in the wettest months and the hottest months had 28.0 oC within the specified period of the study (Table 2).  Total speargrass total dry weight (STDW) increased with rise in rainfall in both locations. Meanwhile, there were variations in the components (Shoot and rhizome) weight. However, there was decline in speargrass dry matter during the dry months (January to April) in the locations. This might have reflected the effects of moisture deficit.  Notwisthanding, Rhizome:shoot varied  at both locations. Derived savanna (Eruwa) had rhizome:shoot >1.00 in five months throughout the study (5/24), while southern Guinea savanna (Kishi) had rhizome:shoot >1.00 in eleven months (11/24). Speargrass control might be more challenging especially in SGS than DS in the months with higher Rhizome:shoot ratio > 1.00. Derived savanna had more months (19/24 months) with lower rhizome:shoot ratio (< 1.00) than SGS (13/24 months). This might have resulted from more rainy months and better distribution of rainfall in Derived savanna for speargrass shoot growth and the resultant decrease in rhizome:shoot (< 1.00). This is a clue for better translocation of herbicides for season-long speargrass control.