The board may classify commercial certificates to be issued under this chapter. The classifications may include pest control operators, wood treaters, ornamental or agricultural pesticide applicators, or right-of-way pesticide applicators. Separate classifications may be specified as to ground, aerial, or manual methods used by any applicator to apply pesticides or to the use of pesticides to control insects and plant diseases, rodents, or weeds. Each classification of certification may be subject to separate testing procedures and training requirements. A person may be required to pay an additional fee if the person desires to be certified in one or more of the classifications provided for by the board under this section.