English: "From the time the sickle is first put to the standing grain" — this teaches that the mitzvah of the Omer is to bring it from standing grain.
On the daf / in context: The Omer must be reaped from grain that is still attached to the ground, so that the reaping itself is performed for the sake of the mitzvah.
Type of Learning
Derash on the verse (Menachos) — the Omer is taken from standing grain.
What Is Learned
The Omer offering must be reaped from grain that is still standing in the field.