Summary.The relative susceptibility of six commercial sugarcane varieties to diuron previously described was confirmed in a second similar experiment. A significant correlation was found between the susceptibility of these varieties to 10 kg/ha diuron and their rooting characteristics. The more susceptible varieties were found to produce larger sett‐roots and smaller shoot‐roots, both of which also tended to be more easily injured by diuron. The root injury appeared as‘burnt’root tips resulting from contact with the layer of soil treated by the herbicide. The roots of tolerant varieties seemed to be immune to such injury and continued growing after penetrating the contaminated soil layers. Retarded plant growth appeared to result from the root injury.Uptake of diuron through shoot‐roots of the susceptible variety F 156 resulted in 68·5% growth retardation. This damage was reduced by 15·5% if the plants were allowed to develop sett‐roots from two‐bud cutting. Death of the plant resulted when both root systems received the same do