In practice, organic farms are required to use pesticides as a last resort, whereas conventional farms use as much pesticide as they feel is necessary routinely. Furthermore, pesticides that are approved for organic use are non-selective, meaning that they must be applied carefully or they will damage the crop. Modern conventional agriculture is dominated by selective herbicides that are used in volume, because the crops are resistant to their effects. This means that the amount of pesticide used by a conventional farming operation dwarfs that of an organic farm.