Weeds are plants growing where they are not wanted. Many different types of weeds occur in cassava farms and cause considerable losses to the farmer. Weeds are among the major constraints to cassava production, and for cassava farmers to be successful, they must control weeds. Weed control in cassava can be done manually, mechanically, culturally, or chemically (use of herbicides). Manual weed control involves the use of hand/hoe. Mechanical weed control entails the use of motorised weeders. Cultural methods such as the use of cover crops, hand hoe, correct spacing, tillage, and cassava variety also help in the control of weeds. As we know, weeds compete with the cassava crop for nutrients, sunlight, and space. Weeds may harbor pests and diseases or physically injure cassava plants and storage roots. Weeds may also harbor natural enemies that control pests, so certain weeds can be left on cassava farms, provided they are not many enough to compete with the crop. The presence of weeds limits the productivity of cassava, and negatively impacts farming families. Weeding takes 50 to 80% of the total labor budget of cassava growers.





Field trials were carried out over a three year period to evaluate the effectiveness of hand-weeding frequencies and several herbicides for weed control in cassava (Manihot esculenta Crantz). Uncontrolled weed growth caused 40% reduction in root yield of short, profusely branching cassava cultivar while a 68% reduction in root yield was observed in separate studies involving a tall non-branching cultivar. Two or three properly timed hoe weedings gave crop yields that were as good as keeping the plots weed free throughout the growing season. Although pre-emergence application gave good weed control and crop yield, the efficacy of these herbicides was greatly improved when 2 or more herbicides are tank mixed. Excellent crop yield was also observed per Ha basis. At current labour rates in Nigeria, it is cheaper to practise chemical weed control in cassava than to rely on hand-weeding even if the labour is readily available and the weeding can be carried out on time.

Chemical weed control is playing an increasing role in Nigerian agriculture due to the increasing cost and widespread unavailability of the labour required to carry out traditional practices. Nigeria’s drive towards increased food production must involve a systematic approach to weed control based on a good understanding of weed biology and ecology. The objectives of such an approach must be the development of effective control methods which are efficient in the use of available resources and within the reach of the farmers.

Weeds need light to be able to grow. They will grow on bare soil and where there is a lot of light. If there are already other plants growing and shading the ground, then weeds will not grow as well. They can develop from seeds or other parts of the plant that remain in the soil. Therefore it is important to prepare the ground properly before planting.
Management
The best way to control weeds in cassava farms is to combine different practices especially at land clearing, ridge preparation, planting and post planting stages of growing the cassava.

Prepare the land properly by slashing the bush before planting. This will reduce the frequency and labour of weeding the crop. Pull any weed from the land and near the land before planting.





Grow cassava varieties that suppress weeds. Early branching varieties form a thick canopy that shades the ground before too many weeds can grow.

Mulch cassava seed beds with dead plants. Use leaves from alley crops, leguminous plants and rice husks to cover the soil surface. This will block out light to the soil and make it difficult for weeds to grow.

Crop rotation reduces weeds.

Between the cassava plants grow other crops like grain legumes and vegetables to reduce the amount of bare



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