Midrasch zu Wajikra 25:5

3) (Vayikra 25:5) ("The after-growth of your harvest you shall not reap, and the grapes of your guarded vine you shall not glean; a year of rest shall there be for the land.") This is the source for the sages' ban on the after-growths of the seventh year. "and the grapes of your guarded vine you shall not glean": From what is guarded in the land you may not glean, but you may glean from hefker (what you relinquished ownership of.) "you shall not glean": in the (usual) way of the gleaners — whence they ruled: Figs of shevi'ith are not to be cut with a muktzeh (the usual tool), but with a knife. Grapes are not to be trod in a vat, but n a kneading trough. Olives are not to be processed in a (bad) (an olive-press) or in a kotiv (a smaller press), but may be crushed and put into a bedidah (a small press). R. Shimon says: They may also be ground in a bad and put into a bedidah.

4) "a Sabbath of resting shall there be for the land": At the end of shevi'ith, even though its fruits are of shemitah status, it is permitted to do work with the body of the tree; but its fruits are forbidden.