a pair of horizontal rods mounted to be very close to the ground run on either side of a row of stalks . the rods are mounted under harvesting equipment which would harvest the crop from the stalks . the rods are independently biased toward the row so that each of the rods contact and slide along the stalks . the rods are at least partially supported by pendants which hang from the harvesting equipment . the lateral movement of one of the pendants is measured to determine the deviation of the vehicle from the row .