A mower has a plurality of rotary cutters (8) for cutting a crop and a swathing unit (15) for forming a cut crop into a swath. The swathing unit (15) includes an auger (16) and a housing that extends around at least part of the auger and provides a swathing aperture (54) through which cut crop material is ejected to form a swath. The housing includes at least one guide plate (36) that can be adjusted to adjust the width W of the swathing aperture.
