MERCED, Calif. — Jeff Marchini and others in the Central Valley here bet their farms on the election of Donald J. Trump. His message of reducing regulations and taxes appealed to this Republican stronghold, one of Mr. Trump’s strongest bases of support in the state.

As for his promises about cracking down on illegal immigrants, many assumed Mr. Trump’s pledges were mostly just talk. But two weeks into his administration, Mr. Trump has signed executive orders that have upended the country’s immigration laws. Now farmers here are deeply alarmed about what the new policies could mean for their workers, most of whom are unauthorized, and the businesses that depend on them.

“Everything’s coming so quickly,” Mr. Marchini said. “We’re not loading people into buses or deporting them, that’s not happening yet.” As he looked out over a crew of workers bent over as they rifled through muddy leaves to find purple heads of radicchio, he said that as a businessman, Mr. Trump would know that farmers had invested millions of dollars into produce that is growing right now, and that not being able to pick and sell those crops would represent huge losses for the state economy. “I’m confident that he can grasp the magnitude and the anxiety of what’s happening now.”