Integrated management of Imperata cylindrica (Speargrass) in yam and cassava: Weed pressure in crop, crop growth and yield

Abstract

The carry-over effects of different methods used to reclaim speargrass infested lands on weed pressure, the growth and yield of cassava and yam were investigated on farmers' fields. The experiments were carried out in the forest-savannah transition zone of Ghana between 2000 and 2003. The dry weight of speargrass rhizomes varied from 182 g at 5 months after planting (MAP) {17 months after treatment (MAT)} to 175 g at 12 MAP (24 MAT) on the fallow plots and plots from which speargrass was slashed before planting mucuna. There were no rhizomes on the ploughed plots that were planted to mucuna and those that were sprayed with glyphosate or hoed before mucuna was planted at 5 MAP. The residue from mucuna suppressed speargrass for about 5 months after senescence resulting in more vigorous and taller cassava plants and cassava root yields of 110-118% greater for the glyphosate+mucuna plot than that of the fallow plot. Hoeing followed with mucuna gave root yields of 53-85% greater than fallow. The tuber yields of yam due to the carry-over effect of glyphosate alone, resulted in 12% increase in yields over fallow plots. Hoeing followed with mucuna resulted in tuber yield 50% greater than fallow whilst using glyphosate+mucuna gave 112% increment in tuber yields. On the ploughed plots, tuber yields of yam were 61% greater than that for fallow plots when mucuna was cropped for one season and 76% greater for mucuna cropped for two seasons. Growing mucuna on ploughed plots for one season was just as effective as cropping for two seasons in smothering speargrass. The results show a significant carry-over effect of an initial cultivation of the soil and mucuna and glyphosate+mucuna to control speargrass for about 5 months in a succeeding cassava and yam crop. © Academic Journals Inc.