Tapioca (Manihot esculenta Crantz) is a high carbohydrate tropical tuber crop relished for its taste by the people of Kerala. Both the method of planting adopted and growth habit of cassava gives opportunities for luxurious weed growth during the initial stage of the crop and hence the crop is prone to weed competition during the first 2-3 months after planting. The present study was carried out with the objective of identifying a good pre emergence herbicide for tapioca as a labour saving and cheaper option. Diuron was the most effective herbicide as evidenced by the lowest weed dry matter production and highest weed control efficiency (WCE). This was not found a good herbicide in tapioca intercropped with legume either for green manure or grain purpose due to the 100% mortality of the green gram.  In legume intercropped tapioca, fluchloralin  0.75 kg/ha resulted in good weed control with a cost saving of 60% over hand weeding.  In a pure tapioca crop the herbicide Diuron 2 kg/ha resulted in excellent weed control with least cost.  A saving of 86% in costs was effected compared to manual weeding.