The director shall adopt regulations that govern the use of 2,4-D and any other herbicide which he finds and determines is injurious to any crop that is being grown in any area of the state. The regulations of the director may prescribe the time when, and the conditions under which, a restricted herbicide may be used in different areas of the state. They may provide that a restricted herbicide shall be used only under permit of the commissioner or under the direct supervision of the commissioner, subject to any of the following limitations:
(a) In certain areas.
(b) In excess of certain quantities or concentrations.