An implement control system includes desired draft force setting apparatus and draft force sensing apparatus providing a draft force signal. It also includes engine speed sensing apparatus arranged to provide an engine speed signal of the same form as the draft force signal. The draft force signal and engine speed signal are averaged and compared with the set desired draft force to produce an error signal which is used to control the movement of the implement. The system is particularly suitable for the control of engine driven implements such as stone-breakers and rotivators where it prevents the engine stalling under heavy load, it is, however, suitable for use with fully-mounted, semi-mounted and trailed implements.