On a recent, perfect morning at Johnson Farms in northern Michigan, workers climb wooden ladders high up into the trees, picking bags strapped across their bodies. The branches are heavy with fruit that glows in the morning sun. Their fingers are a blur, nimbly plucking fruit and filling bushel bags: about 50 pounds per load. It's hard, sweaty work.

Apple season was just getting underway on Old Mission Peninsula, a finger of land poking into Lake Michigan, dotted with lush farms.

The pickers range in age from 21 to 65, and all of them are Mexican. As in the rest of the U.S., growers in heavily agricultural northern Michigan rely overwhelmingly on migrant laborers to work the fields and orchards.

According to the farm owners, the workers either came from Mexico on temporary H2A visas or they have paperwork showing they are in the U.S. legally.

Farmers from Georgia to California say they have a problem: not enough workers to harvest their crops.

It's estimated anywhere from half to three-quarters of farmworkers are in this country illegally, and some growers say that President Trump's anti-immigrant rhetoric has made a chronic worker shortage even worse.

Johnson Farms' owner, Dean Johnson, 67, says it's just about impossible to find Americans to do this work. "We've tried. We really have," he says. "Sometimes people come out on a day like today and they'll pick one box, and then they're gone. They just don't want to do it."

"It's really sad," adds Johnson's daughter, Heatherlyn Johnson Reamer, 44, who manages the farm. "They'll come, they'll check it out, and usually they're gone within a day or two."

What's behind the farmworker shortage?

For one, a stronger U.S. economy is driving many seasonal workers into better-paying, year-round work, like construction.

"There's a huge need in the trades," Reamer says, "especially when we have natural disasters like we've seen these last few years with the hurricanes and everything. And we've actually lost workers who said, 'Hey, I got a job. I'm gonna go work for this construction company in Florida.' And they would leave."

Another factor: The children of migrants are upwardly mobile and are leaving the fields behind. Many are going to college and finding better work opportunities in professions outside agriculture.

Add to that Trump's crackdown on immigration, which many growers complain is crimping their labor supply. "As we all know, there's a pretty good number of workers in this country illegally," Dean Johnson says. "They're scared. Those people don't want to travel anymore. They're in Florida and Texas. They won't come up from Mexico."

"There wouldn't be food"

Johnson says even though Trump's aggressive stance on immigration hurts him as a grower, he did vote for him last November. "I was in favor of change," he says. "There's other things involved, besides the immigration issues."

His daughter, Heatherlyn, disagrees. "I was actually very disappointed that Michigan voted for [Trump]," she says. "We need someone who supports agriculture, someone who supports diversity in this country."

The president's talk about building the border wall leaves her cold: "When we heard that, I said, 'You can't say things like that.' There are so many migrant workers in this country. You just wonder, do you really see who your population is?"

Without migrant workers to pick the crops, Reamer says, "There wouldn't be food. It's just as simple as that." She mentions Michigan's asparagus crop of 2016, which had to be mowed under because there weren't enough workers to pick it.

Looking around her orchard, Reamer says, "The one thing the population doesn't understand, for farmers like us — without the migrant labor, this doesn't happen. You won't have apples in your supermarkets; they just won't get picked. Because, unfortunately, the average Joe in the United States doesn't want to go out and do this job for 10 hours a day."

Because of the farm labor shortage, many farms across the country are relying more heavily on workers from Mexico, brought in through the H2A temporary visa program. The workers earn $12.75 an hour, at minimum, plus transportation and housing.

Farmers complain that the program is cumbersome. There's a lot of red tape, with multiple federal agencies involved, and it's expensive: It can cost about $2,000 in fees for each worker they bring in. But the growers need the help. Nationwide, the H2A program has grown by 81 percent over the past five years.

Workers are afraid and "nobody wants to come"

Across Grand Traverse Bay, a migrant worker named Marcelino — who asks that we not use his last name because he fears being deported — is at home in the trailer he shares with his two daughters and his wife, Leticia, who is busy making tortillas for dinner.

Marcelino and Leticia are both undocumented; they work side-by-side in the fields. Their daughters are U.S. citizens, born in Michigan.

Marcelino tells me he grew up in the Mexican state of Guerrero. "My home is in the rural, rural place," he says, a village of 20 homes, so small it doesn't even have a name.

He crossed the border illegally in 1989, when he was just 14, to work in the fields. He has lived in this country ever since.

In the winter, the family lives in Florida, where Marcelino and his wife pick oranges.

Come March, they head north to Michigan for field work — cherries, grapes and apples. The girls switch schools, back and forth.

Marcelino has been making the trip for 28 years now. In the past, he says, migrant families would drive north in a long caravan, seven or eight vehicles, all filled with workers. Now, he says, "Nobody wants to come." They're too afraid, Marcelino says, and he's fearful, too. His friends in Florida tell him he's crazy to make the trip, but he needs the work, and, he says, he doesn't want fear to rule his life.

Asked what he would say to people who argue that the U.S. is a nation of laws, and that undocumented workers are taking jobs away from Americans, Marcelino says:

"I'd tell them, come work with us, and if you like the work, and if you produce as much as we do, then here is your job."

He notes that one of his bosses tells him he would need to hire 10 people to do the work he does.

Looking ahead, Marcelino dreams of a better life for his daughters, who have a boost up as American citizens. One wants to be a police officer; the other, a surgeon.

He warns his girls: Pay attention in school and study hard, or else you could end up like us, coming home from the fields, all dirty and stinky.

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