A mower has a plurality of rotary cutters for cutting a crop and a swathing unit for forming a cut crop into a swath. In some embodiments, the swathing unit includes an auger and a housing that extends around at least part of the auger and provides a swathing aperture through which cut crop material is ejected to form a swath. In some embodiments, the housing includes at least one guide plate that can be adjusted to adjust the width W of the swathing aperture.