Any person violating any provision of sections 21.111 to 21.121 or any rule promulgated by the commissioner thereunder shall be guilty of a misdemeanor; and upon conviction for a first offense shall be punished by a fine of not less than $25 nor more than $1,000 or by imprisonment for not less than 10 days nor more than 90 days; and for each second and subsequent offense such persons shall be guilty of a gross misdemeanor and shall be punished by a fine of not less than $50 nor more than $3,000 or by imprisonment for not less than 30 days nor more than six months. Upon conviction for such second offense the commissioner shall refuse the violator the privilege of handling in any way certified seed potatoes during the season in which such second offense was committed.