Two field experiments were conducted during the 1986 wet season at Samaru in the northern Guinea savanna ecological zone of Nigeria to study the effects of mulching, periods of weed interference and chemical weed control ginger (Zingiber officinale Roscoe). In the weed interference trial, the use of grass mulch resulted in lower weed infestation and vigorous growth of ginger compared with the unmulched plots. Mean dry rhizome yield in mulched plots was about 37% higher than that of the unmulched situation. Mulching also resulted in lower weed dry matter production compared with no mulching due to the effect of grass mulch which suppressed weed growth through smothering. It was also apparent in this trial that weed infestation for 4 weeks after planting (WAP) did not adversely affect crop growth due to initial slow growth of the crop. Maximum rhizome yield could be obtained even when the crop is allowed to be infested up to 12 WAP due to lack of crop injury which usually occurs during weed removal at early stages of growth. Probably the critical period of weed competition in the crop is between 12 and 16 WAP. It was apparent that all the herbicide treatments consistently controlled weeds effectively both before and after one supplementary weeding. Among the weed control treatments, mixtures of metolachlor with chlorbromuron and prometryne, each at 1.0 + 1.0 kg a.i/ha, terbutryne at 1.33 + 0.67 kg a.i./ha metribuzin at 1.0 to 0.25 kg a.i./ha, fluometuron and ametryne, each at 1.0 + 1.0 and 1.5 + 1.5 kg a.i./ha and with diuron at 1.0 + 0.4 and 1.5 + 0.8 kg a.i./ha, all followed by supplementary hoe-weeding at 13 weeks after planting, resulted in significantly higher rhizome yield and effective seasonlong weed reduction compared with the unweeded control . Except the mixtures of metolachlor with fluometuron, ametryne and diuron, high rates of the other herbicide mixtures did not differ significantly in rhizome yield from the unweeded check, thus indicating possible detrimental effect of increasing the rates of these mixtures for weed control in the crop. It was apparent that atrazine-containing mixture was not tolerated by this crop, since both rates resulted in poor crop vigour and low rhizome yield comparable to the unweeded control. In this trial, unchecked weed growth throughout the crop life cycle significantly depressed crop vigour, leaf, stem and shoot dry weight and number of leaves per plant. It also reduced rhizome yield by 50.3% and 63.0% compared with the appropriate best treatments in the weed interference and chemical weed control trials, respectively