Abstract
After the first crop, taken from a forest clearing, broadleaf weeds accounted for 85% of the weed population in the unweeded plots. A dramatic change in the weed flora occurred m the second crop with grasses accounting for an average of 77% of the weed flora in the unweeded plots. In the maize (Zea mays L.) plots, the shift to grasses was more pronounced when herbicides were used, an average of 83% of the weeds were grasses. The shift towards grasses continued in the third cropping season. Weeds caused a significant yield reduction in all crops in the first cropping season. In the second crop, yield loses due to weeds were greater when cowpea [Vigna unguiculata (L.) Walp.] was planted after cowpea than when cowpea was planted after maize. In the third crop, except in the continuous maize cropping pattern, yields of maize were not significantly increased by weeding. For cowpea and soyabean [Glycine maz (L) Merr.], yields were significantly increased by weeding but were not affected by cropping pattern.
