Halakhah for Chullin 261:1

From the laws of the commandment is, for example, that which they, may their memory be blessed, said (Chullin 137a) that it is one, whether he is a harvester (cutter) or a plucker, he is liable for the corner - and even though the verse stated, "In your harvesting," [it is] not specifically [about] a harvester. And if he transgressed and harvested everything (Bava Kamma 94a), he gives a little of the harvested [produce] to the poor. And that which they, may their memory be blessed, said (Chullin 131a) that there is no [right] for the owners to benefit [by choosing who receives] the favor, but rather [the poor can] take it against their will. And the law of from when is any person permitted to them. And that which they, may their memory be blessed, said (Chullin 134b) that if there are no poor to take the corner, that the owner of the field is permitted to take it; as it is stated, "to the poor and to the stranger," and they, may their memory be blessed, expounded, "and not to the ravens and to the bats." And they, may their memory be blessed, gave this general principle about the obligation of the corner, whether from the produce or whether from the trees: Any food that grows from the ground, is guarded, cut all at once and brought in to be preserved - for example produce, legumes, carobs, walnuts, almonds, grapes, olives and that which is similar to them that have these five [characteristics] that we said - is obligated in the corner. But woad and rubia and what is similar to them are exempted because they are not food; and so [too,] truffles and mushrooms are exempted because they are not guarded; and so [too,] figs are not obligated since their cutting is not at once; and so [too] vegetables are exempt, because they are not brought in to be preserved (see Shabbat 68a).