The commissioner shall issue a certificate of inspection annually for nursery stock grown in licensed nurseries within the state found to be practically free from damaging pests. Certificates expire on December thirty-first each year unless canceled at an earlier date. Certification may be withheld by the commissioner when nursery stock is infested with a pest or if weeds or other objects prevent an adequate inspection of the nursery stock. All nursery stock being offered for sale within the state must be from officially inspected sources. A copy of a certificate of inspection from the state of origin must accompany each commercial lot or shipment of nursery stock that is transported into or offered for sale within North Dakota. All copies of the North Dakota certificate of inspection required for shipping purposes must be approved by the commissioner.