In order to provide a machine with a better maneuverability, a microprocessor-based steering controller was designed and developed for an over-the-row apple harvester. The controller allowed the machine operator to select any one of the five steering modes which were: (1) auto-steer, (2) front only, (3) four way, (4) crab, and (5) rear only. Upon recognizing the selected steering mode, the controller executed the appropriate algorithm which performed the necessary wheel position control. As a part of the controller, absolute shaft encoders were designed. The encoders were used to sense the position of the wheels and the tree sensor arms. In each steering mode except auto-steer, the tracking ability of the rear wheels was determined. For the auto-steer mode, the ability of the apple harvester to reamin centered over a tree row while moving over the row was evaluated.