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Opium poppy growers in southern Mexico who helped fuel the U.S. heroin epidemic say prices for their product have been driven so low — apparently by the use of synthetic opioids like fentanyl — that they are turning in desperation back to another crop they know well: marijuana.

Beset by poverty and joblessness, farmers in the hills around the Guerrero state hamlets of Tenantla and Amatitlan say that prices for opium paste — which oozes from the bulbs of poppies after they're cut — have fallen so low they don't even pay for the cost of planting, fertilizing, irrigating, weeding and harvesting the raw material for heroin.

One local farmer points to a former opium poppy field tucked into the fold of steep hillside. The dried stalks of the poppy plants from last year's harvest can be seen sticking out among the 2- and 3-foot-tall stands of marijuana planted this year.

"We'll probably keep planting both," said the stocky farmer who asked not to be named for fear of arrest.

But a rail-thin grower with narco-style chain necklaces in the nearby hamlet of Amatitlan said he won't plant poppies again.

"If I'm working three months to make just 5,000 pesos ($250), I might as well do something else," he said. "It's easier to plant marijuana. It isn't so prone to pests."

What has him and other farmers in the region desperate is a huge drop in the prices that local drug gangs pay for a kilogram of opium paste. At its height a few years ago, the farmers say they could get 20,000 or 25,000 pesos ($1,000 to $1,250) per kilogram. This year, prices have dropped to 5,000 ($250) per kilo.

The farmer in Amatitlan blames the price drop on the "sinteticos" — synthetic opioids like fentanyl. Drug cartels are increasingly either selling fentanyl in pill form or cutting heroin with fentanyl to boost its potency, thus lessening their need for naturally grown opioids.

That's already having an effect on America's opioid problem as well, according to U.S. law enforcement.

"Some heroin indicators suggest fentanyl is significantly impacting market share and, in a few markets, even supplanting the heroin market," the Drug Enforcement Administration said in its 2017 National Drug Assessment report.

A U.S. official, who was not authorized to be quoted by name or agency, noted that for traffickers, there are advantages to synthetics. They are not affected by rainfall, raids or rival gangs and can be ordered by mail from Chinese labs, avoiding much of the labor and conflict involved in buying small amounts of opium paste from farmers and processing them into heroin and then smuggling it to the U.S. market.

Still, DEA figures indicate the flow of organic heroin has been high and rising in recent years, and the official estimated it could take five to 10 years for growth of fentanyl to put a significant dent in that.

There's still "plenty of heroin flowing north," the official said.

However, officials in Guerrero state — one of Mexico's largest growing areas, together with northern states like Durango, Chihuahua and Sinaloa — say that on the ground, they're already seeing the effects of the drop in opium prices.

"The increase in synthetic drugs is causing the price of naturally grown drugs like opium to fall, and that is hitting the income of the criminal groups," said Guerrero state security spokesman Roberto Alvarez.

"The gangs are experiencing an economic crisis, which is causing criminals to diversify their activities," said Alvarez, noting that some gangs have taken to carjacking vehicles on the heavily travelled toll highway that runs from Mexico City to Acapulco, something that didn't use to happen.

"They are turning to extortion or kidnapping, as well," Alvarez notes. "All of a sudden they see their income drop and so they seek out other revenues, like kidnapping, extortion."

This month, for example, a city on the other side of the mountains in Guerrero saw its local PepsiCo distribution plant close because of gang extortion demands — just months after the Coca Cola plant there closed for the same reason. Such large companies had previously gone largely untouched by gang violence.

Government figures suggested opium eradication nationwide remains strong and may even be rising: In the first four months of 2018, soldiers destroyed 12,834 hectares (31,713 acres) of opium poppies, and only 720 hectares of marijuana.

But that also suggests that the Mexican army is placing a higher focus on eradicating poppies than on marijuana; after all, the army has seized an average of 850 tons harvested and dried marijuana annually in recent years, suggesting there are hundreds of thousands of acres under cultivation.

Anecdotally, farmers in Guerrero say authorities do focus more on eradicating opium. They point to at least one field in a narrow valley that was sprayed with an herbicide by a government plane about three months ago; no marijuana plots have been raided in the same valley.

Locals say farmers have been planting both crops here since at least the 1970s, and prices for both have fallen steadily. Bulk marijuana that once sold for as much as $40 per kilo now sells for $10. Farmers don't make much money on either crop.

The deciding factor for many farmers is the cost and effort involved. Opium poppies must be irrigated, well-fertilized, must get regular applications of pesticides. Harvesting opium is a delicate, time-consuming task: the poppy bulb is cut and carefully scraped, often by farmhands who can collect only a small amount each day.

While some farmhands charge as little as $7 per day, poppy workers charge double that, eating up any potential profit. Marijuana isn't as prone to plant pests, and harvesting is simpler.

And there is also the possibility that marijuana growing might be legalized. Mexico has already approved some personal-use growing, though it hasn't legalized commercial crops.

Some think legalized, commercial marijuana growing might help these mountain villages, which have been plagued by violence since opium surged in price and warring gangs fought for control of the area. Heavily armed vigilantes with assault rifles now patrol hamlets like Tenantla 24 hours per day.

Humberto Nava Reyna, the head of the Supreme Council of the Towns of the Filo Mayor, a group that promotes development projects in the mountains, said, "We all know the economy of this region, the high mountains of Guerrero, has been based on growing marijuana and opium poppies. ... What we are asking is that be regulated and regularized."

In larger terms, it is all just another chapter in the desperation-driven, cyclical farming history of the tropics, with farmers living through booms in crops like coffee, only to see them bust because of plant diseases or price drops.

"Back in the 1970s, farmers planted more marijuana, and when the marijuana went down, opium poppies went up, and now they're looking to turn to regulated marijuana growing," said Nava Reyna.