Bava Metzia 106 - General vs. Localized Calamities

If a tenant-farmer leased a field from his fellow and locusts ate up the crop or it was blasted by wind, which blew the kernels out of the ears of grain, if it is a general calamity, he may deduct from his rental. Since the whole area was stricken, his field is considered unfit for crops, and the tenant committed himself to pay full rental only on the assumption that the field would remain suitable for crops for the duration of the lease.
If the loss was localized, the owner can claim that it was the farmer's ill fortune, and the farmer may not deduct from his rental.