משנה על שמות 26:35

Luf of the sixth year that has entered the seventh year, similarly summer onions and puah (madder) grown in good soil: Bet Shammai says: they must be uprooted with wooden rakes. Bet Hillel says: [even] with metal rakes. They agree in the case of puah with strong roots, that they may be uprooted with metal spades.