A Self-propelled mower-conditioner (10) is proposed. The mower-conditioner (10) has a frame (12) supported for traveling over a field of crop at a variable ground speed, a header (22) supporting a driven crop cutting arrangement (24) across a forward region of the header (22), a windrow forming arrangement located at a rear region of the header (22) and a driven crop conveying arrangement (30, 32) located for receiving cut crop from the cutting arrangement (24) and delivering the cut crop to the windrow forming arrangement (30, 32), and a crop conveying arrangement speed control (50). To avoid plugging of crop, the mower-conditioner (10) further comprises a ground speed sensor (96) providing an electrical ground speed signal indicative of the forward ground speed of the mower-conditioner (10) an electronic controller (70) coupled for receiving the ground speed signal (98) and being coupled for sending a control signal (140) to a controllable drive device (102) of the conveying arrangement (30, 32) and said electronic controller (70) being responsive to a decrease in ground speed for sending a control signal (140) to the drive device (102) of the conveying arrangement (30, 32) for decreasing the speed of the drive device (102) of the conveying arrangement (30, 32) by an amount proportional to a sensed decrease in ground speed.
