A method of cruise control for a harvester automatically monitors certain operating conditions of the harvester and responsively sets an engine speed value adequate to meet predicted torque demand, and, but not necessarily, automatically varies a propulsion speed of the harvester as required to match the torque demand to the available torque to increase efficiency, and has particular applicability to a sugar cane harvester. Monitored conditions can include certain characteristics or parameters of a pump or pumps powering fluid operated systems of the harvester, in particular, propulsion and harvesting systems. Other conditions can include intake air temperature, coolant, and hydraulic fluid temperature. Rate of change of one or more of the conditions can be used for setting the engine speed and to predict the torque demand.