Abstract: A method and apparatus for guiding an agricultural implement having transversely extending arms by spraying the ground with a band of a fluorescent chemical from an end of one of the extending arms of the agricultural implement to mark the end of the area covered by a first pass of the agricultural implement, directing an optical beam having a width substantially greater than the band of fluorescent chemical onto the band of fluorescent chemical to fluoresce a portion of the band of fluorescent chemical which produces a fluoresced region on the band of fluorescent chemical, and positioning a detector on the band of fluorescent chemicals to detect the fluoresced region on the band of fluorescent chemical to determine the position of the implement with respect to the fluoresced region and thereby maintain the implement on course.