Effects of Types and Duration of Weeds on Yield Parameters of Cocoyam ( Xanthosoma saghtifolium )

Weeds reduce yields of all tropical crops significantly, and these effects vary with different species. Thus, the influence of time of weed control and types of weeds on yield parameters of cocoyams ( Xanthosoma sagittifolium ), a tropical tuber crop, was determined by two experiments conducted simultaneously. In one experiment, weeds were removed at different times during crop growth. In the other, different weed types were removed selectively to leave either one or two of the identified categories, namely grasses, broadleaves and sedges. The presence of weeds throughout the growth cycle of the crop reduced yields of cocoyams by 60 %. Removal of weeds at early growth stages produced greater yields than weeds were present beyond 18–22 weeks after planting. The presence of weeds at the time of tuber initiation had the greatest adverse effect on yield parameters. Weeds had a delaying but not an inhibitory effect on cormel initiation. However, all other yield parameters were reduced by weeds. Broadleaved weeds, which have similar growth patterns as cocoyams reduced yields to a greater extent than grasses. Sedges had no significant impact on cocoyams. The presence of grasses and broadleaves together reduced growth and yields of this crop to a greater extent than any other combination.