Abstract: A control apparatus for use with two opposed ground markers of an agricultural machine comprises a hydraulic circuit including a plurality of hydraulic valves for communicating fluid actuate movements of the marker cylinders and an electrical control system including a plurality of manually operable actuating switches to effect operation of said hydraulic valves. Each of the switches provides an output in response to a single actuation thereof and there is provided an output timer operable to effect operation of the hydraulic valves for a period of time sufficient to effect a stroke of the cylinders. The electrical control system provides an output in response to actuation of selected ones of the switches only in response to actuation of the switch for a predetermined time period sufficient to avoid inadvertent actuation.