Apparatus for cutting vegetation with a rotatable head carrying a non-metallic cutting line (31) extended into a cutting plane. As the line extension decreases from an established preset length an actuator in the head permits additional line to be extended automatically from a supply source within the head. The actuator imposes a back pressure (F₃) against the line of magnitude correlated to the sensed pull tension wanting to extend the line outward of the head. After the cutting line length is extended to its restored original preset length, the actuator in response to the operational forces imposed thereon secures the cutting line against further extension until a subsequent decrease in line extension is incurred. In one embodiment an iner­tial drag brake (68) is activated during the course of line feedout and is deactivated after the length of cutting line has been fully restored.