On and after May 1st through October 31st of each year, the application of use restricted herbicides is prohibited daily from three hours prior to sunset to sunrise the following morning: Provided, That if there is a mean sustained legal wind velocity of not less than five miles per hour the application of use restricted herbicides is allowed in Areas 3 and 4 up to one hour prior to sunset in all counties as restricted by rule except Benton, Franklin, Yakima, and Walla Walla counties.