It shall be a violation of this chapter to transport by highway any hay, straw, or grain which has been purchased by weight or will be purchased by weight, unless it is weighed and a certified weight ticket is issued thereon, by the first licensed public weighmaster which would be encountered on the ordinary route to the destination where the hay, straw, or grain is to be unloaded: PROVIDED, HOWEVER, That this section shall not apply to the following:

(1) The transportation of, or sale of, hay, straw, or grain by the primary producer thereof;

(2) The transportation of hay, straw, or grain by an agriculturalist for use in his or her own growing, or animal or poultry husbandry endeavors;

(3) The transportation of grain by a party who is either a warehouse operator or grain dealer and who is licensed under the grain warehouse laws and who makes such shipment in the course of the business for which he or she is so licensed;

(4) The transportation of hay, straw, or grain by retail merchants, except for the provisions of RCW 15.80.430 and 15.80.440;

(5) The transportation of grain from a warehouse licensed under the grain warehouse laws when the transported grain is consigned directly to a public terminal warehouse.