Positive Mitzvah 124
Leaving Individual Fallen Grapes in the Vineyard
Leviticus 19:10 "Neither shall you gather the single grapes of your vineyard, you shall leave them for the poor and for the stranger"
While picking the produce in his vineyard, it is likely that some grapes may fall.
The Torah commands us to leave those individual fallen grapes so the poor people may collect them for themselves (see Negative Mitzvah 213).
Negative Mitzvah 213
It is forbidden to gather individual fallen grapes
Leviticus 19:10 "Neither shall you gather the single grapes of your vineyard"
While picking the clusters of grapes from the vines some individual grapes may fall off.
We are not allowed to pick these grapes up, but rather, we must leave them for the needy.
Positive Mitzvah 122
Leaving a Forgotten Sheaf while Reaping
Deuteronomy 24:19 "If you have forgotten a sheaf in the field, you shall not go back to fetch it, it shall be for the stranger, for the fatherless and for the widow"
Even after the reaping in the field has been concluded, there is still another opportunity for the farmer to supply the poor man with his needs.
The produce, which by now has been piled in bundles, must be collected.
If a bundle is forgotten, the farmer may not go back to collect it. It must be left in the field for the needy people (see Negative Mitzvah 214).
Negative Mitzvah 214
It is forbidden to collect a forgotten "Omer" of grain in the field
Deuteronomy 24:19 "(When you reap your harvest in your field) and you have forgotten a sheaf in the field, you shall not go back to get it"
When we reap our harvest and forget an "omer", which is a sheaf of grain, we may not go back to fetch it. We must leave it for the needy.