I rent out a house with a small grove of apple trees; although the renters have rights to the yard, the apples are mine?

I have been gathering apples either for my own use or to sell by the basket. My tenants have been taking so many that I barely have any for myself. Are the apples my right to keep or theirs?
Update: I only gave them rights to use of the yard, not the fruit. They must be giving them away, because it's a LOT of apples! I wouldnl't have minded a few, but they are stripping them bare.
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