If it is found that any license or certificate issued or approved by the commissioner of agriculture is being used in connection with nursery stock or other plants which have not been inspected, or which are infested with insect pests or infected with plant diseases, or which are being sold and delivered without treatment being given or other precautionary measures prescribed by the commissioner of agriculture being observed by the owner, or is being used by persons other than the one to whom it was issued with the knowledge of the owner without permission of the commissioner of agriculture, the commissioner of agriculture may require the owner of such license or certificate to appear before him, on a date specified, for a hearing to show cause why his license or certificate should not be revoked. If after such hearing, the commissioner of agriculture finds that such license or certificate has been wrongfully used in 1 or more of the ways specified in this section, or if the owner of such license or certificate fails to appear at such hearing he may issue an order revoking such license or certificate and the owner’s license and the use of such certificate or license after it has been revoked, shall be unlawful and shall subject the owner thereof to the penalty prescribed in section 26 of this act. The commissioner of agriculture may withhold a license or certificate of inspection from any person applying for the same if such person fails to comply with the requirements of the commissioner of agriculture with reference to freeing his nursery and premises of injurious insect pests and plant diseases and may refuse to certify a nursery if the same is in such condition that it can not be adequately inspected.