Thieves recently broke into a storehouse in this farming town high in the Andes, knocked the manager over the head and made off with 2,600 pounds of contraband. Trucks have been surreptitiously crossing the border, laden with an illicit substance bound for China. And with the price of their signature crop soaring, once-poor farmers bounce along the unpaved roads in shiny new vehicles.

The precious stuff that has provoked sudden larceny and luxury here is not drugs, gems or precious metals. It is a pungent, turnip-like vegetable called maca, heralded as a cancer-fighting superfood and sold on the shelves of supermarkets like Whole Foods.

It is so popular in China for its perceived aphrodisiac effects that this year Chinese buyers showed up here with suitcases full of cash to buy up the harvest, inciting a gold rush and setting off alarms from Lima to Los Angeles and beyond.

As maca booms, some Peruvians fear that they are losing control of a valuable crop with a history that goes back long before the time of the Inca empire.

Officials say that many Chinese buyers smuggled the root out of the country in violation of a law that requires maca to be processed in Peru before it can be exported — a measure intended to protect local businesses. They say seeds were also smuggled out of the country illegally, despite a ban meant to prevent the root from being grown anywhere else.

“Thousands of acres are being grown outside the country without authorization,” said Andrés Valladolid, the president of Peru’s National Commission Against Biopiracy.

Oswaldo Castillo, a maca grower and processor, worried that the Chinese “will get a monopoly over maca and be able to set the price on the world market.”

He warned that some farmers had sold maca seeds to Chinese buyers.

“We can’t let the seeds leave the country,” he said. “Maca is our ancestral food. It’s our pride.”

The Chinese buying spree and the clandestine export of whole maca and seeds has raised questions about the ability of developing countries to control access to native species.

But it has also stunned buyers of the root in the United States, Europe and Japan, who suddenly saw prices of processed maca shoot up, or were told that there was simply no maca left to ship to them.

Zach Adelman, the founder of Navitas Naturals, based in Novato, Calif., one of the top importers in the United States, said that his company previously paid about $3.60 a pound for maca powder. Now some suppliers are asking for more than $20 a pound.

“It doesn’t look like it’s coming down or stabilizing even,” Mr. Adelman said. At Whole Foods stores, the price of his organic maca, labeled “Incan superfood,” recently increased to $30 a pound from as low as $20. Next year, he said, shoppers will pay up to $80 a pound. “It’s going to hit them like a ton of bricks in the new year when they go and find a bag that’s three times as much,” he said.

Some scientific studies claim to show a link between consuming maca and an increase in libido. Such beliefs go back centuries. One historical account says that the Inca emperor fed maca to his troops to give them energy but removed it from their diet after victorious campaigns to tame their sexual desire.

Maca had all but disappeared as a crop by the 1980s but began a comeback in the 1990s, promoted by the government and aided by its reputation as an aphrodisiac. According to Peru’s Ministry of Agriculture, there were 6,227 acres planted with maca in 2012, up from 3,207 in 2010. Acreage appears to have grown significantly since then, and farmers said they planned to increase their plantings even more to meet the new Chinese demand.

In June, as the harvest started, Chinese buyers arrived in this town of 10,000 people, which sits at 13,555 feet above sea level on a bleak plain surrounded by windswept, dun-colored hills.

Within weeks, the vegetable, a member of the mustard family with a pungent smell and taste, soared in value, from about $1.80 a pound to more than $11 a pound for the most sought-after variety.

Fortunes were made overnight.

“It has changed my life,” said Pilar Cóndor, 25, standing beside her new black Toyota HiLux pickup truck, her 7-month-old baby, Kenny, wrapped in a colorful shawl on her back. “Not many people my age can buy a pickup truck based on their work.”

She said that her family, which together farmed about 250 acres of maca this year, also built an addition to their house and bought a truck to transport harvested maca. A day earlier, she said, they sold nine tons of maca for about $7.80 a pound, which adds up to more than $140,000.

Many of the Chinese who bought maca this summer loaded the dried vegetables onto trucks and sent them clandestinely across the border to Bolivia, according to government officials. That hurt local processors. But of greater long-term concern were news reports that farmers in China had begun growing large amounts of maca. Mr. Valladolid, the biopiracy official, said those plantings could have been started only with seed smuggled out of Peru illegally.

Because maca rapidly depletes the soil, sucking out its nutrients, farmers typically plant a field for only two years, after which it must lay fallow for as long as 15 years. That has forced farmers to go farther and farther away to find land to plant, often tilling dizzyingly steep hillsides.

That is the problem faced by Hugo Arias, 53, considered by many here to be the maca king for his extensive plantings. This year, he farmed more than 600 acres and said he would increase that 20 percent for next year’s crop. He said he had used much of this year’s profit to buy farm equipment and rent more land to grow maca. He is also building a large new house in town.

On a recent day, Mr. Arias exhorted about 200 workers harvesting maca, in a field at a breath-sapping 14,800 feet, to work harder. A frigid wind blew mist across the pampa as vicuñas grazed on yellowed tufts of coarse grass.

“They say I’m exploiting people,” said Mr. Arias, wearing only a light windbreaker against the cold. “I don’t exploit anyone. I give people work.”

Out of earshot of Mr. Arias, some workers said that despite receiving a raise this year they were not benefiting enough from the stunning rise in maca prices. They are paid $11.37 a day, they said, up from $9.65 last year.

The harvesters, including some women with babies on their backs, knelt down to scrape the earth with short-handled picks to expose the maca roots, which range from about two inches across to the size of a small fingernail.

It is hard to imagine that anything can grow in this harsh landscape besides lichen and wild grasses. But the maca is well adapted to the conditions, its pale green, frisee-like leaves hugging the cold ground.

Victor Parra, 56, one of the workers, said it was so cold sometimes that he could barely pick the maca out of the soil. The harvesters were given short rest periods, he said, and brought their own food and water. They travel to and from the fields in the back of cramped trucks.

“A kilo of maca is how high?” Mr. Parra said. “So why do they pay us so little and treat us badly?”

The price jump has also brought trouble. Growers said they were staying up at night to guard drying tents and storehouses from thieves. Their worries increased after the storehouse of a Japanese buyer was raided. The company’s local representative said that the thieves hit him on the head, then loaded sacks of dried maca into a pickup truck.

“I never thought the price of maca would go so high,” said the man, Alex Rojas, 33, who said the thieves threatened to shoot him.

Junínos, as residents here are called, typically consume maca two or three times a week, at breakfast. They boil the root and blend it with milk, fruit and sugar, turning it into a hot drink called maca juice. But with the rising price, many now forgo the staple.

“The poor person in Junín can’t eat maca anymore,” said Olga Rapri, 48, who has a clothing shop in town. “Now you have to be rich to have maca.”

She said sales at her store had increased as money poured into town during the harvest, but less than she had hoped.

“People would rather buy cars, motorcycles, tractors, seed,” Ms. Rapri said. “They would rather invest in growing more maca.”