A mower for cutting grass comprises a traction frame that is self-propelled over the ground by a power source carried on the traction frame. The mower includes a thumb wheel throttle control that progressively increases and decreases the power output of the power source as the thumb wheel is rotated in one direction or an opposite direction. The thumb wheel has a plurality of tabs that define grooves on an arcuate rim on the thumb wheel for receiving a thumb or index finger of one of the operator's hands.