DES MOINES, Iowa — The Republican nomination in Iowa's 3rd Congressional District will be decided by a convention after none of the six candidates reached the 35 percent threshold required to make the general election ballot.

The vote in Tuesday's primary was split between state Sen. Brad Zaun, Secretary of State Matt Schultz, biofuels association director Monte Shaw, construction company owner Robert Cramer, physical education teacher Joe Grandanette and David Young, a former aide to Sen. Charles Grassley. Zaun was leading with 24.6 percent of the vote with nearly all precincts reporting.

The winner will run in November against Democrat Staci Appel, a former state senator who didn't have a primary opponent.

Party leaders will announce a convention date soon.

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The crush of Republican candidates followed 10-term Republican Rep. Tom Latham's decision to retire.

The southwest Iowa district stretches from Des Moines to Council Bluffs.