Iowa Code § 43.39: Ballot for another party’s candidate.

If any primary elector writes upon the elector’s ticket the name of any person who is a candidate for the same office upon some other party ticket than that upon which the candidate’s name shall be so written, such ballot shall be so counted for such person only as a candidate of the party upon whose ballot the candidate’s name is written, and shall in no case be counted for such person as a candidate upon any other ticket.