were also selected at similar intervals. Field size varied from smallholdings of less than 0.25 ha to large government cassava multiplication farms of a size of several ha. Sites were selected to cover as wide a range as possible of different climatic conditions, cultivation techniques, cultivars and soil types (Cardwell et al., 1997). Data from a second survey conducted in 1994 in four West African countries including Benin and Ghana (Wydra and Msikita, 1998) could not be evaluated in combination with these data since site selection and data collection differed due to the broader area covered in the latter survey.