Upon written request, the secretary may issue a permit to use herbicides within or in the proximity of an area affected by an order issued pursuant to section 3,¹ if he shall find that such use is reasonably necessary for its purpose, and the proposed manner of use will not be harmful to the grapevines or grape crops which the order is intended to protect. Every such permit shall prescribe the manner of use, either as proposed by the permittee or as the secretary may deem necessary to avoid harm to such grapevines or grape crops.