Abstract: A single disc field marker comprises a support arm pivotally mounted on the end of the sprayer boom and carrying on its end a rotatable disc. The disc is supported so that in one position it lies in a plane which is substantially vertical and parallel to the direction of motion of the boom and can be adjusted readily by movement of the support arm through 90 to a second position in which the outer surface of the disc is inclined so the top edge is outward of the bottom edge and the rear edge is inward of the front edge. The first position can be used to form a furrow in bare land and the second position can be used with standing crop to gently lie the crop to one side.