In harvesting by hand, the sickle is used to cut the crop, and the rake is used to gather it up. In the literal sense, the rake comes behind the sickle in this process.
The poet makes repeated mention of curves to describe womanly shapes and motions. The sickle is used in a curving motion, while the rake is used in repeated linear motion, consistent with the sexual metaphor that Cherry mentions, in the "prodigious mowing". In Scottish dialect, "mowing" means to have sexual intercourse. A "rake" is also a licentious and dissolute man.