The department may require a person producing, selling or offering for sale or shipping or transporting any nursery or florist stock within the state to affix or have printed on each package of stock a certification statement as prescribed by the department. When a certification statement is required, it is unlawful for any transportation company, public carrier, commercial truck or other agency engaged in the business of transportation to ship, transport or accept for shipment any package of nursery or florist stock until the required certification statement is attached to the package.