A windrower (1) useful for collecting stalk material from a field (43) and depositing the material In a windrow (61). The collection of dust and debris in the windrow is minimized by the use of a screen (24) located above the auger (29) which transports the cut stalk material to a discharge chute (14). The screen (24) permits lighter airborne particles to escape from the region surrounding the auger (29) before they are entrained and deposited into the windrow. A screen (47) is also placed beneath the auger (29) to permit small, dense particles to fall from the region surrounding the auger and be deposited on the ground (43). A flexible barrier (48) is placed between the auger and the cutting assembly (32) so that material falling through the screen is not reintroduced to the cutting blades (39, 42). A second barrier (64) is positioned behind the auger so as to form a volume (66) within which material is confined so that it will not become airborne. The windrower wheels (3-10) are adjustably spaced and arranged in pairs so that the number of individual wheels riding on a peak contour (56) within the field (43) is maximized.