S.D. Codified Laws § 12-5-3.8
If a political party chooses to have a primary for selection of its delegates and alternates to the national convention, the party shall certify the candidate names or the delegate and alternate slates which are to be listed on the primary ballot to the secretary of state by the last Tuesday in March preceding the primary by five p.m. central time. Only candidates or slates certified may be placed on the ballot by the secretary of state and the position of the candidates or slates on the primary ballot shall be chosen by lot by the secretary of state. The certification shall be deemed to be submitted if mailed by registered mail by five p.m. central time on the last Tuesday in March. If a political party does not choose to have a primary selection of its delegates and alternates to the national convention, the party shall define the selection process of its delegates and alternates in the party bylaws.
SDCL 12-5-3.8