During the rainy season, farmers in the West African cotton belt concentrate their physical and financial efforts on attempting to control weeds. Their priorities at the start of the season are sowing and weeding food crops; the plots intended for cotton are then cleared, generally using animal-drawn ploughs, which often results in only superficial, irregular tillage. The weed clearance provided by tillage is particularly shortlived if the weeds are only partially dug in, and weed problems increase the later the crops are sown. Farmer practices in northern Cameroon for land preparation and weed control have changed substantially as a result of R&D programmes. In 1976, Cameroon was the first French-speaking African country to introduce pre-emergence herbicides on cotton and maize crops, under an intensification drive including tillage with light machinery. Paraquat, which was introduced in 1987 and initially only used in mixtures with pre-emergence herbicides, is now very widely used, and has contributed to the success of direct seeding on a weed mulch. Glyphosate has been used since 1996, following the introduction of diuron and atrazine in 1992, which replaced the binary products distributed previously, hence cutting costs and significantly increasing the areas of cotton and maize treated. These four generic herbicides are now a driving force in changing cropping systems. Within cotton-maize rotations, chemical weeding facilitates integrated control type approaches. However, herbicides can increase weed invasion problems when used as part of an extensification strategy. The organisational conditions that enabled the impressive development of chemical weeding in northern Cameroon included the integration into the cotton commodity channel of training, monitoring, logistics and credit operations.