All leaf tobacco offered for sale in a leaf tobacco warehouse shall be weighed by a public weighmaster or a deputy weighmaster acting under the public weighmaster’s instructions, and shall be accompanied by a public weighmaster certificate. It shall remain in custody of the warehouse operator from and after the time it is weighed by the public weighmaster until it is sold or the bids are rejected by the owner thereof. The provisions of this section shall not be effective until July 1, 1968.