Farmers showed a strong preference for Republican presidential candidates in recent elections. So it’s not surprising a convincing majority are ready to vote for billionaire businessman Donald Trump over former Secretary of State Hillary Clinton.

Related: 5 things Republicans say they'll do for ag

But while both candidates consolidated their positions after bruising primary campaigns, one in six growers responding to our latest Farm Futures survey said they may not vote for either of the two major party hopefuls.

Trump led Clinton 73% to 10% in the survey of 1,178 farmers July 18-Aug. 3. But “none of the above” came in a strong third place, selected by 7% of growers. Libertarian Gary Johnson was at 4%, about the same as those who said they do not intend to vote. Another 2% selected a write-in candidate, while Green Party nominee Jill Stein was preferred by only 1 producer.

Related: Trump scores big with farmers

Clinton was the top choice among Democratic-voting farmers since we started surveying farmers a year ago. She appears to have attracted all the Bernie Sanders’ supporters in farm country. Trump started out the cycle with just 20% of the farm vote in a crowded Republican field. But as the number of his opponents shrank, his numbers rose.  By our March poll he was the clear leader, though still at only 29%.

Related: How Hillary looks to change rural America

But even in March, almost 18% were undecided or not planning on voting, a figure that is little changed from the total not supporting Clinton or Trump now.

As for issues in the election, “the way the government works in Washington” remains the top concern of farm voters. But farmers are less worried about other hot button issues like immigration, terrorism or wealth and income inequality. Instead, their other two top issues are the budget deficit and the economy.

Related: Farmers still back Trump in Farm Futures poll

With farmers accounting for less than 1% of the nation’s population, agriculture won’t decide the election – at least directly.

But our research shows that since 1960 corn prices have a perfect track record in predicting winners and losers for the White House. If corn prices rise between Sept. 1 and the election, history says Trump should win. Corn prices rose before each of the elections when presidency changed from Democratic to Republican hands. That included Richard Nixon in 1968, Ronald Reagan in 1980 and George Bush in 2000.

Related: U.S., Iowa farmers favor Trump in Farm Futures poll

By contrast, when the Democratic candidate emerged victorious from these party “change” elections, corn prices fell. That happened with John Kennedy in 1960, Jimmy Carter in 1976, Bill Clinton in 1992 and Barrack Obama in 2008.

Corn prices also dropped every time the incumbent president was succeeded by a member of the same party, Republican or Democrat. That suggests lower corn prices this fall would forecast a victory by Clinton.

Related: The next president's ag policies

Of course, corn prices have a seasonal tendency to drop into fall most years, regardless of politics. Corn is a powerful crop, but it may not be a real king maker.