Management of Cogongrass (Imperata cylindrica) with Velvetbean (Mucuna pruriens var. utilis) and Herbicides

Field experiments were conducted in 1992 to 1993 and in 1995 to 1996 in Iba dan, Nigeria, to assess the effect of velvetbean and herbicides on maize (c orn) and cogongrass growth and to assess regrowth of the weed 1 yr after tr eatment. In 1992 and 1995 cover cropping with velvetbean and imazapyr and g lyphosate application reduced cogongrass density as much as the handweeded control, The smothering effect of velvetbean was equivalent to that of glyp hosate at 1.8 kg/ha but was less than imazapyr even at the lowest rate of 0 .5 kg/ha. Addition of adjuvant did not improve the efficacy of either herbi cide. Maize grain yield was higher in velvetbean plots than in fallow plots dominated by cogongrass. Velvetbean and herbicide effects on cogongrass 1 yr later (1993 and 1996) followed a similar trend as observed in the year o f application. Annual weed density was highest in glyphosate plots, followe d by imazapyr, and least in plots previously seeded to velvetbean. Maize gr ain yield was higher in herbicide plots (average yield of 3,170 and 1,920 k g/ha in 1993 and 1996, respectively) than in velvetbean plots (2,800 to 1,1 80 kg/ha in 1993 and 1996, respectively) and handweeded plots (2,890 and 72 3 kg/ha in 1993 and 1996, respectively). In 1996 the lowest maize yield was in handweeded plots without velvetbean, suggesting that weeding four times suppressed cogongrass density and biomass, but was not sufficient to minim ize the subsequent competition from annual weeds, Uncontrolled cogongrass r educed maize yield to zero. These studies suggest that planting velvetbean for cogongrass control may be a better alternative for farmers without the resources to purchase herbicides.