Sap flow was measured, with Granier-type sensors, in a crop of field-grown water-stressed cassava (Manihot esculenta Crantz) in Ghana, West Africa. The main objective of this study was to examine the environmental control of canopy conductance (g c ) with a view to modelling the stomatal control of water transport under water-stressed condition. Weather variables measured concurrently with sap flow were: air temperature (T a ), relative humidity (RH ), wind speed (u) and solar radiation (R s ). Relationship between canopy conductance (g c ) and vapour pressure deficit (D ฮต ) was curvilinear while no specific pattern was observed with R s . Average diurnal g c decreased from 3.0 ยฑ 0.6 to 0.7 ยฑ 0.4 mm s -1 between 0730 and 2000 h local time (= GMT) each day. A Jarvis-type model, based on a set of environmental control functions, was parameterized for the cassava crop in this study. Model results demonstrated that g c was estimated with a high degree of accuracy based on R s , T a , and D ฮต (r 2 = 0.92; F = 809.2; P < 0.0001). D ฮต explained about 90% (F = 2129.7; P < 0.0001) of the variations observed in g c , whereas both R s and T a contributed about 2% of the explained variance in g c . The aerodynamic conductance (g a ) was very high compared to g c , leading to a daily average ratio g a /g c > 100 and a decoupling factor< 0.1. Cross-validation analysis revealed a consistent good performance (r 2 > 0.85) of the g c model with D ฮต as the only independent environmental variable.