|Abstract||A weed can be defined as an unwanted plant, or as a plant growing in the wrong place. Plants which are useful in their right places become weeds if they grow where they are not wanted. Guinea grass for instance is a useful plant in a grazing paddock but a bad weed in a canefield. Some plants are weeds wherever they grow, because they are a nuisance in useful land, or are harmful to the health of man or livestock. Weeds in sugar cane fields cost the grower money. When these pests are controlled better crops are produced which are also less expensive to harvest. Weeds compete with crops for water, sunlight and mineral nutrients. They increase costs of labour and equipment, reduce the quantity and quality of the product, and harbour diseases, insects and other pests. They are amongst the greatest obstacles to mechanizing production completely. Better burns, lower cutting costs and improved surface drainage result from a good weed control programme. At least half the cultivation which is required is on account of weeds. It has been estimated that the economic loss clue to weeds on farms is greater than that caused by insects and diseases combined. A good weed control programme includes the use of good cultivation methods as well as chemicals. The use of chemicals alone cannot be expected to give the best results. Most weeds of cultivated land mature and produce seed before the crop in which they grow is harvested.